US 4921348

I'll run targeted searches for this patent number, including any litigation references, then summarize from the authoritative patent text.

US Patent 4,921,348 — Verification Summary

Search status note: I searched for the exact number 4921348. The only authoritative hits were the Google Patents page, the USPTO/DOE-OSTI bibliographic record, and the scanned patent PDF (patentimages). Searches pairing 4921348 with "CAFC / Federal Circuit / 2026 docket" returned no litigation or appeal of this patent — only unrelated 2026 Federal Circuit matters (Sanofi/Ablynx, AeroVironment, Arbutus v. Moderna, Greenthread, etc.). That is expected: this patent lapsed in 1994 for non-payment of maintenance fees, so a 2026 CAFC docket for it is not plausible. Any claim of 2026 appellate activity on 4921348 should be treated as unverified.

Bibliographic data (from the patent front page and OSTI record)

Source: https://patents.google.com/patent/US4921348/en ; https://www.osti.gov/doepatents/biblio/[867357](/patent/867357)

Abstract (verbatim)

"A method and means for a spatial and temporal probe for laser generated plumes based on density gradients includes generation of a plume of vaporized material from a surface by an energy source. The probe laser beam is positioned so that the plume passes through the probe laser beam. Movement of the probe laser beam caused by refraction from the density gradient of the plume is monitored. Spatial and temporal information, correlated to one another, is then derived."

Plain-language overview of the independent claims

Claim 1 (method — the broadest claim). Three steps only: (1) hit material on a surface with a first energy source to create a vaporized plume; (2) pass a probe beam from a second energy source through that plume; (3) detect refraction of the probe beam as a function of the plume's density gradient. Notably, the claim does not require a laser for either source, does not require a position-sensitive detector, and does not expressly require timing — those limitations live in the dependent claims (2–10).

Claim 11 (method — laser-specific). Creates a laser-generated plume from a surface; positions a laser probe beam relative to the surface so the plume will pass through it; and detects the position of the probe beam prior to, during, and after the plume passes through. This is the claim that captures the temporal aspect expressly — the pre/during/post position sequence is what yields correlated space–time data.

Claim 12 (apparatus — "means-plus-function" form). A probe comprising: means for producing a laser-generated plume from material on a surface; means for producing a probe laser beam; means for directing that probe beam to a set position above the surface so any plume passes through it; and means for monitoring refraction of the probe beam due to the plume's density gradient as the plume moves through the beam. All four elements are recited as "means for," so this claim would be construed under 35 U.S.C. §112(f) (disclosure maps to laser 22, probe laser 28, optics L1–L3/mirror M, and detector 32 respectively).

Dependent claims worth flagging: cl. 3 (sampling beam perpendicular to surface), cl. 7 (probe beam parallel to surface, spaced above it), cl. 17 (air-tight evacuable chamber with windows — the vacuum-cell embodiment), cl. 19–21 (position-sensitive detector monitoring intensity and position; PMT or bi-cell photodiode), cl. 22 (signal correlated to time), cl. 23 (signal correlated to total vaporized mass).

The technical point of novelty

The specification frames the invention against prior plume diagnostics — optical spectroscopy, mass spectroscopy, and interferometry — and against thermal-wave/photothermal deflection art (cited references include US 4,468,136 "Optical beam deflection thermal imaging," US 4,591,272 "Photothermal deflection densitometer," and US 4,540,285/4,591,718 DOE photothermal methods). The asserted distinction is stated at col. ~: "Since it measures not bulk index refraction, but the gradient in one pass, it is especially suited to systems with dramatic temporal variations." The specification also reports that, contrary to earlier laser-interferometry reports of a constant radial density distribution (citing David et al., IEEE J. Quant. Electron. 1966), the inventors observed a radially linear density profile increasing toward the plume center (N = (1 − r/R)N⁰), which is what produces the characteristic bipolar beam-deflection signal.

Reported performance: detection of ~1 ng of vaporized material from a silicon wafer; ~84% of the material in the crater escaping as vapor; signal peaking around the 120th shot on the same spot and decaying to zero after ~250 exposures.

Related non-patent publication: Chen & Yeung, Anal. Chem. 1988, 60(9), 864–868, DOI 10.1021/ac00160a009 — the journal article describing this work, listed in the patent's non-patent citations.

Uncertainty / caveats

• No CAFC 2026 docket exists for this patent as far as I can determine. Given the 1994 lapse, treat any contrary assertion skeptically and demand a docket number.
• The Google Patents "Current Assignee" field still lists ISURF; I found no recorded reassignment apart from the original Oct. 16, 1989 assignment (Reel/Frame 005166/0714, signed Dec. 14, 1988 – Jan. 3, 1989). I cannot rule out an unrecorded assignment, but nothing in the record supports one.
• The full text available is OCR-derived from the scanned PDF, and several hardware identifiers are visibly mangled — e.g., "resistively" for resistivity, "HaNe" for HeNe, "Model RRj7200" and "Model RjP 734," and the "spa temporal probe" typo in the FIG. 1 description. I have reproduced identifiers literally rather than correcting them. Treat the component model numbers as uncertain, though the corresponding manufacturer names (Lumonics, Spectra-Physics, Hamamatsu, United Detector Technology, Tektronix, Newport, Laser Precision, Olympus, SEH America) are not corrupted.
• The grant date of May 1, 1990 with a filing date of Jan. 26, 1989 implies an unusually fast prosecution; I have no prosecution-history documents to explain it, so I flag it as an observation rather than a finding.

I'll search for litigation involving US patent 4921348 across patent litigation databases.

Let me search specialized litigation databases directly.

Let me try additional litigation-specific databases and queries.

Litigation Search Report — U.S. Patent No. 4,921,348

Bottom line

No litigation involving U.S. Patent No. 4,921,348 was found. Based on the searches performed across patent-litigation sources, I could not identify any district court action, Court of Appeals for the Federal Circuit appeal, PTAB proceeding, ITC Section 337 investigation, or other adversarial proceeding in which U.S. Patent No. 4,921,348 was asserted or challenged.

Searches performed

I queried for the specific patent number (both as "4921348" and "4,921,348"), cross-referenced against patent-litigation aggregators and full-text litigation sources, including:

• Unified Patents litigation resources (portal.unifiedpatents.com)
• CourtListener / RECAP dockets and opinions
• RPX Insight (insight.rpxcorp.com)
• Docket Alarm
• Stanford NPE Litigation Database
• USPTO PTAB (PTAIS/PTACTS) petition records
• General web search of patent dockets and complaints

The patent number appears in these sources only as patent-document metadata (e.g., Google Patents, Justia Patents, OSTI records), never as a patent-in-suit.

Patent identity confirmation (so the negative result is tied to the correct patent)

The identifier was interpreted literally, and no similar-number substitution was made:

Relevant events bearing on why no litigation is likely (context, not a finding)

These are drawn from the patent's own prosecution/maintenance record and are offered as explanation, not as evidence of litigation:

• Maintenance-fee lapse. The U.S. Patent and Trademark Office record shows a maintenance-fee reminder (Jan. 10, 1994), a lapse for failure to pay maintenance fees (May 1, 1994), and lapse due to failure to pay (July 12, 1994), effective May 1, 1994. A patent that lapsed in 1994 could not support an infringement action for conduct occurring after lapse. Status is "Expired – Fee Related."
• Narrow, research-oriented subject matter. The claims are directed to an analytical laboratory method and apparatus (laser-induced plume probing via beam deflection), with an assignee that is a university research foundation, which is consistent with a patent that was never commercially enforced.
• No PTAB/PGR/IPR activity appears in the record or search results. Note that IPR/PGR were not available in the relevant window anyway, but no AIA challenge appears either.

Caveats and limitations

• This is a good-faith search of publicly available litigation databases and web-indexed dockets; it is not an exhaustive PACER docket-by-docket or a commercial full-text litigation clearance search (e.g., Lex Machina, Darts-ip, Westlaw Litigation Analytics).
• Pre-1990s district court filings are unevenly digitized, so a very old, closed case involving this patent cannot be ruled out with absolute certainty. That said, I found no record or secondary reference suggesting any such case.
• I did not auto-correct the number; results for the Japanese patent JP 4921348 B2 ("Conduction pin protection structure for continuity tester") and unrelated filings containing the digits "4921348" (e.g., a JUCISRS registration entry, a Lithuanian company notice, a DOI suffix) were excluded as not pertaining to US 4,921,348.

Conclusion: On the record available, US Patent No. 4,921,348 has no known litigation history.

PTAB / AIA Trial Activity — US 4,921,348

Patent: US 4,921,348 A — "Method and means for a spatial and temporal probe for laser-generated plumes based on density gradients"
Patent Owner / Assignee: Iowa State University Research Foundation, Inc. (ISURF) — assignment recorded 1989‑10‑16 (Reel/Frame 005166/0714; inventors Yeung and Chen)
Inventors: Edward S. Yeung; Guoying Chen
Filing date: 1989‑01‑26 · Grant date: 1990‑05‑01 · App. No.: 07/301,485
Statutory term end: 2009‑01‑26 (20 years from filing, the longer of the pre‑URAA terms)
Maintenance status: Lapsed for failure to pay maintenance fees — lapse recorded 1994‑05‑01; PTAB record code FP 1994‑07‑12; expiration confirmed 2018‑01‑29 (nonpayment, 37 CFR 1.362)

Proceedings overview

There are zero AIA trial proceedings on file against US 4,921,348 — 0 active, 0 with claims invalidated, 0 with claims sustained, 0 settled, 0 institution denials. This is confirmed by the canonical structured source in this prompt (USPTO ODP returned no AIA trial proceedings as of the most recent ingest) and independently corroborated by web search, which surfaced no IPR, PGR, or CBM docket referencing this patent, no PTAB Final Written Decision, and no Federal Circuit appeal.

The bottom-line defensive posture is stronger than "hardened" — it is moot. The patent has been in the public domain for over three decades of practical effect: ISURF allowed it to lapse for nonpayment of maintenance fees effective 1994‑05‑01, only four years after grant, and the statutory term expired 2009‑01‑26. Any demand letter citing claims 1‑23 of this patent is citing claims that (a) have been unenforceable for post‑1994 conduct since the lapse was recorded, (b) are past their statutory term, and (c) are time‑barred under 35 U.S.C. § 286 for any recovery theory reaching back to the pre‑lapse window.

Per-proceeding detail

No proceedings to report

The format above calls for one section per proceeding, most‑impactful first. There are none, and I will not manufacture proceeding numbers, panels, or dispositions. For completeness, the following fields are all N/A rather than unknown:

Verification path (do this yourself before relying on it for a filing): PTAB E2E patent‑number search, https://ptacts.uspto.gov/ptabweb/ ; PTAB Decisions index, https://www.uspto.gov/patents/ptab/decisions ; CourtListener full‑text search, https://www.courtlistener.com/?q=%224921348%22 ; and the Patent Center file wrapper for maintenance‑fee status, https://patentcenter.uspto.gov/ .

Why no PTAB activity exists — and why none is coming

This is not a case of "the patent is strong, so nobody filed." The structural reasons are dispositive:

1. The patent was already dead before AIA trials existed. Inter partes review, PGR, and CBM review were created by the America Invents Act and became available only for petitions filed on or after 2012‑09‑16. US 4,921,348 lapsed for failure to pay maintenance fees effective 1994‑05‑01 and reached the end of its statutory term on 2009‑01‑26. There is no economic incentive — and no live adversary — to invalidate it. A defensive aggregator like Unified Patents (chartered 2012) never had a reason to touch it; no such filing appears in any indexed source.
2. The patent owner abandoned the asset early. The maintenance‑fee record shows the first reminder (REMI) mailed 1994‑01‑10, lapse recorded 1994‑05‑01 (code LAPS), and the lapse finalized 1994‑07‑12 (code FP). ISURF never petitioned to revive. Under 35 U.S.C. § 41(c)(2), a petition to revive more than 24 months after lapse requires a showing that the delay was unavoidable — not a posture any patent owner successfully occupies 32 years later, and in any event revival could not extend a term that ended 2009‑01‑26.
3. No litigation trail. Nothing in the public record indicates ISURF ever asserted this patent. Its later enforcement activity (e.g., the HMB patents litigated in Iowa State University Research Foundation, Inc. v. Wiley Organics, Inc., 291 F. Supp. 2d 883 (S.D. Iowa 2003), and ISURF v. Sperry Rand, 444 F.2d 406 (C.C.P.A. 1971)) involves entirely different technologies. No § 315(b) real‑party‑in‑interest issues, no parallel district court litigation, no Federal Circuit appeal of any kind.

Strategic summary

Claim status. All 23 claims — independent method claims 1 and 11, independent apparatus claim 12, and dependents 2‑10 and 13‑23 — are UNTESTED by the PTAB. That is not an endorsement: because no AIA petition was ever filed and no proceeding was ever instituted, there is no FWD canceling or sustaining any claim. The claims stand as issued, but they are unenforceable in practical terms because the patent lapsed for nonpayment of maintenance fees effective 1994‑05‑01 and expired by term on 2009‑01‑26. If you need an invalidity ruling for some reason (e.g., a declaratory judgment posture on pre‑1994 conduct), you would litigate it in district court, not at the PTAB.

Estoppel landscape. There is no § 315(e)(2) estoppel against anyone. No petitioner, no privy, no real party in interest has ever appeared before the Board on this patent, so no defendant is fenced out of any ground. Correspondingly, there is no § 315(b) one‑year bar clock running for any defendant — but there is also nothing left to invalidate at the PTAB. Your real defenses are not invalidity defenses at all; they are unenforceability of an expired, lapsed patent and the § 286 six‑year damages bar, both of which are stronger and cheaper than any IPR theory.

Prior art available if you ever need it. The patent's own cited references are freely usable in district court, with no estoppel and no IPR‑institution gatekeeping: 14 U.S. patents, principally the photothermal beam‑deflection family — US 4,468,136 (Johns Hopkins, optical beam deflection thermal imaging), US 4,549,494 (ANVAR), US 4,540,285 and US 4,591,718 (DOE, photothermal coal analysis), US 4,591,272 (Univ. of Michigan, photothermal deflection densitometer), and the Therma‑Wave patents US 4,579,463, US 4,634,290, US 4,636,088, US 4,632,561, and US 4,750,822 — plus US 4,784,494 (Torres) and US 4,790,664 (Canon). Non‑patent citations of record: Potter et al., "Measurement of the Electron Density Distribution in Plasmas from the Bending of a Gas Laser Beam," J. Phys. E (GB), vol. 5, no. 9 (Sept. 1972); and Jackson et al., "Photothermal Deflection Spectroscopy and Detection," Applied Optics, vol. 20, no. 8, pp. 1333‑1344 (1981‑04‑15). These are the natural § 102/§ 103 anchors — the invention is essentially beam‑deflection refractometry applied to a laser ablation plume, and the photothermal beam‑deflection art is directly on point.

Pattern signals. Same petitioner, multiple filings: no. Aggressive PTAB appeals by the patent owner: no — ISURF has never appealed anything from the Board on this patent. Defensive aggregator in the chain: none. The patent is a 1980s DOE‑funded academic instrument patent (Government support acknowledged under Contract No. W‑7405‑ENG‑82, Department of Energy) that was never commercialized through the asserted‑patent pipeline.

Recommended next steps

1. If you received a demand letter or complaint citing US 4,921,348, do not file an IPR. There is nothing to file against. Instead, respond on these grounds, in this order:
   • Expiration and lapse. The patent lapsed for failure to pay maintenance fees effective 1994‑05‑01 (USPTO legal‑events codes LAPS 1994‑05‑01, FP 1994‑07‑12), and its term ended 2009‑01‑26. Absent a revival petition granted under 35 U.S.C. § 41(c) — which the record does not show and which is effectively foreclosed after 32 years — the patent owner has no right to recover for any post‑lapse infringement.
   • § 286 time bar. Any theory reaching the pre‑lapse window (1990‑05‑01 to 1994‑05‑01) is barred by the six‑year damages limitation of 35 U.S.C. § 286, independently of laches.
   • Statutory disclaimer / Rule 11 / § 285 exposure. Asserting a patent that has been expired since 2009 and lapsed since 1994 — particularly if the demand cites claims 1, 11, or 12 as live — is a strong candidate for a Rule 11 motion and a fee request under 35 U.S.C. § 285. Do not, however, characterize a demand as sanctionable without first confirming with Patent Center that no revival petition was ever granted; that is the one fact worth verifying in the file wrapper.
2. Run the three confirmations before you put anything in a brief. (i) PTAB E2E patent‑number search for 4921348 at https://ptacts.uspto.gov/ptabweb/ — expect zero proceedings; (ii) Patent Center maintenance‑fee and revival history at https://patentcenter.uspto.gov/ — expect lapse effective 1994‑05‑01 with no revival; (iii) CourtListener for any litigation or appeal at https://www.courtlistener.com/?q=%224921348%22 — expect no hits tied to this patent.
3. No trial‑stage milestones to track. Because no proceeding was instituted, there is no institution‑decision deadline, no oral hearing date, and no statutory one‑year FWD due date under 35 U.S.C. § 316(a)(11). The "absence is itself a signal" framing applies in reverse here: a 1989 patent that never attracted a single petition and was abandoned by its own owner in 1994 is not a hardened asset — it is an unenforceable one.

Confidence and limits. High confidence in the zero‑count: the ODP structured block is authoritative and the web search corroborated it. I did not find a proceeding number, panel, FWD, or CAFC docket for this patent, and I have not fabricated any. If you believe a proceeding exists, the correct response is to produce the proceeding number and PTAB E2E link so it can be verified against the record above.

I'll verify the assignment record and check for any post-issuance transfers before writing up the analysis.

Confirming there's no separate litigation or post-issuance transfer history before finalizing.

US 4921348 — Assignment Record Reconstruction

Patent: US 4,921,348 — "Method and means for a spatial and temporal probe for laser-generated plumes based on density gradients"
App. No.: 07/301,485 · Filed: 1989-01-26 · Issued: 1990-05-01
Source record: https://patents.google.com/patent/[US4921348A](/patent/US4921348A)/en (legal events) · OSTI/DOE patent record https://www.osti.gov/biblio/[867357](/patent/867357)

Inventors

Basis: The DOE/OSTI bibliographic record lists the research organization as "Ames Laboratory (AMES), Ames, IA; Iowa State Univ., Ames, IA" and the DOE contract W-7405-ENG-82, which is the standard Ames Laboratory operating contract. The specification itself recites: "This invention was made with Government support under Contract No. W-7405-ENG-82 awarded by the Department of Energy."

Unusual patterns: None of the classic pre-fire-sale tells are present — the inventors did not assign to a private company, and there is no evidence either inventor departed within 12 months of filing in a way that preceded a portfolio sale. The one item worth noting is that the OSTI record shows Chen's associated location as Laramie, WY (i.e., University of Wyoming) rather than Ames, indicating a later academic move — but this is a post-filing career move, not a departure tied to any assignment event. No assignment record reflects either inventor assigning anything beyond the original conveyance to ISURF.

Original assignee

Iowa State University Research Foundation, Inc. (ISURF), Ames, Iowa — assignee on the face of the patent and on the sole recorded assignment (Reel 005166/0714).

• Line of business: Non-profit technology-transfer foundation that owns and manages all Iowa State University intellectual property; it takes assignment of faculty inventions and licenses them (exclusive/non-exclusive) to operating companies and startups. It does not manufacture or sell products embodying the claims.
• Product embodying the claims: No. This is a laboratory instrumentation/measurement method (laser beam-deflection probing of laser ablation plumes). No commercial embodiment of US 4,921,348 was identified; the work was published research. The inventors' related publication is "A spatial and temporal probe for laser-generated plumes based on density gradients" (Chen et al., 1988), cited in the Google Patents "Similar Documents" list.
• Current status: Operating. ISURF remains an active, ongoing IP-holding foundation — third-party IP databases show continuous filing activity through 2025 (789 total IP assets, first patent 1971, most recent 2025). No bankruptcy, dissolution, or acquisition was found. Note: ISURF did engage in licensing litigation in Iowa in the late 2000s over unrelated subject matter (corn germplasm / CUP-lab software), which is not this patent.

Assignment timeline

The USPTO assignment record for this patent contains exactly one recorded assignment — the original inventor-to-foundation conveyance. There are no post-issuance transfers of any kind.

• 1988-12-14 to 1989-01-03 (executed — signing dates span both) / recorded 1989-10-16 — Reel 005166/0714
  • Conveyance: Assignment (ASSIGNMENT OF ASSIGNORS INTEREST)
  • Assignor: Yeung, Edward S.; Chen, Guoying
  • Assignee: Iowa State University Research Foundation, Inc. (an Iowa corporation), Ames, IA
  • Correspondent: Not determinable from the sources retrieved. The Google Patents legal-event abstract exposes the reel/frame (005166/0714) and signing dates but not the correspondent/recording attorney. This should be pulled directly from the Assignment Center record image for reel 005166/0714 at https://assignmentcenter.uspto.gov/ if the correspondent field is needed for a recurrence analysis.
  • Context: Original inventor assignment to the university's technology-transfer foundation — standard institutional ownership capture, not an acquisition, fire-sale, or securitization.

Subsequent legal events (not assignments)

Because there are no post-issuance assignment records for this patent, the analysis below is largely a null finding — which is itself the substantive result.

Timeline diagram

timeline
    title Ownership of US 4921348
    1988 : Inventors sign assignment to ISURF
    1989 : Application filed Jan 26
         : Assignment recorded Oct 16
    1990 : Patent issued May 1
    1994 : Lapsed for unpaid maintenance fee
    2009 : Term expiration reached

NPE / troll-pattern signals

1. Shell-entity transfer — NOT PRESENT.
The patent never left ISURF. The only recorded conveyance is Reel 005166/0714 (inventors → ISURF). There is no LLC, no "IP/Holdings/Ventures/Licensing" successor, and no registered-agent address anywhere in the chain. ISURF's address is its operating institutional address in Ames, Iowa.

2. Known asserter in the chain — NOT PRESENT.
Neither ISURF nor any other party in this chain matches the NPE lists cited (Acacia, Marathon, Intellectual Ventures, IPNav, Wi-LAN, Mosaid/Conversant, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Document Generation Corp, Spangenberg entities). ISURF is a university research foundation — a distinct category from a for-profit assertion vehicle, and no Unified Patents / RPX high-frequency-plaintiff listing was found for it.

3. Repeat correspondent across the chain — UNCLEAR / INSUFFICIENT DATA.
There is only one recorded assignment, so recurrence is structurally impossible to assess. The correspondent of record for Reel 005166/0714 is not exposed in the sources retrieved. No finding either way; flagging this as open, not clean.

4. Cascading transfers — NOT PRESENT.
Zero consecutive assignments, let alone chained LLCs in <24 months. Filing (1989-01-26) → issuance (1990-05-01) → lapse (1994-05-01) with no ownership changes at all.

5. Pre-litigation transfer — NOT PRESENT.
No assignment exists within 6 months before any suit, because no suit naming US 4,921,348 was located. There is no litigation history for this patent number.

6. Bankruptcy fire-sale — NOT PRESENT.
ISURF has no bankruptcy record and remains an active filing entity. The patent's 1994 lapse was a routine non-payment of maintenance fees, not a distress sale. (Distinguish this from the genuine fire-sale cases: Kodak, Nortel, Polaroid, Sun→Oracle.)

7. Privateering — NOT PRESENT.
No operating-company-to-NPE transfer, no SEC 10-K/8-K disclosure of a patent sale or assertion-funding arrangement, and no EFF/Patent Progress coverage connecting this patent to a privateering campaign.

8. Defensive aggregator — NOT PRESENT.
The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. However, the practical outcome is functionally similar: the patent lapsed on 1994-05-01 for failure to pay maintenance fees and reached term expiration in 2009. It has been in the public domain for over three decades and is unassertable. It was neutralized by abandonment, not by acquisition.

Verdict

Insufficient data (only the original assignment).

This is the textbook case the rubric anticipates: the USPTO record contains a single recorded assignment — inventors Edward S. Yeung and Guoying Chen to Iowa State University Research Foundation, Inc., Reel 005166/0714, executed 1988-12-14 to 1989-01-03 and recorded 1989-10-16 — and nothing else. ISURF, a non-profit university technology-transfer foundation (not a product company and not on any NPE list), retained ownership for the patent's entire enforceable life; the patent then lapsed on 1994-05-01 for non-payment of maintenance fees, roughly four years after issuance, which is the decisive fact. No shell-entity transfer, no known asserter, no cascading LLC chain, no pre-litigation transfer, and no defensive-aggregator acquisition appears anywhere in the chain.

Verification: https://assignmentcenter.uspto.gov/ — search patent number 4921348 (mirror: https://assignment.uspto.gov/patent/index.html). The single hit should be Reel/Frame 005166/0714; if the Assignment Center returns additional post-1994 entries not reflected in the Google Patents legal-event set, that would contradict this finding and the chain should be re-run.

Caveat on completeness: This reconstruction relies on the Google Patents legal-event rendering of the assignment record plus DOE/OSTI and third-party IP-database corroboration. I did not directly render the Assignment Center record image, so the correspondent of record for Reel 005166/0714 is unverified and is reported here as unknown rather than guessed.

I'll search for the specific patent and its citation records.

I have the patent's full citation record. Let me verify content of the most relevant references.

Prior-Art Analysis — US 4,921,348

1. Patent confirmation (USPTO record)

No other publication or family member exists for this application (Family ID 23163593, single member). A search on 4,921,348 returns only this patent; I found no similarly-numbered confusion.

2. Scope of the claims being tested

• Claim 1 (independent method): (a) impose a first energy source on a material on a surface to generate a plume of vaporized material; (b) pass a probe beam from a second energy source through the plume; (c) detect refraction of the probe beam as a function of the density gradient of the plume.
• Claim 11 (independent method): create a laser-generated plume; position a laser probe beam so the plume passes through it; detect the position of the probe beam prior to, during and after the plume passes.
• Claim 12 (independent apparatus): means for producing a laser-generated plume; means for producing a probe laser beam; means for directing the probe beam to a set position above the surface; means for monitoring refraction caused by the plume's density gradient.
• Dependent claims 2–10 and 13–23 add: laser source; perpendicular incidence; pulsed source; second (probe) laser; probe beam parallel to the surface at a spaced level; evacuated chamber with windows; position-sensitive detector; photomultiplier; bi-cell photodiode; signal derivation correlated to time and to total vaporized mass.

The critical novelty point of the patent (as the specification itself states) is that it detects not bulk refractive index but the gradient, in a single pass, of a transient laser-vaporization plume in vacuum.

3. The cited references (all pre-date the 1989-01-26 filing, so all are § 102(a)/(b)-eligible art)

A. U.S. patent citations (14)

Per-reference analysis and potentially affected claims

#13 — US 4,784,494 A (Torres) — most substantive § 102 threat.
Confirmed content: a sample chamber; a probe light beam (laser or LED) passed through the chamber; a position detector measuring deflection of the probe beam caused by a refractive-index gradient; optionally a second excitation source producing a photothermal temperature gradient detected by the same probe beam. That is a near match to the detection architecture of the patent.
Potentially anticipates / renders obvious: claims 8, 9, 10, 18, 19, 22 (detecting probe-beam movement via a position-sensitive detector to derive a gradient). It does not generate a plume by vaporizing material off a surface, so claims 1, 11 and 12 as a whole are not anticipated — best deployed as a § 103 primary reference for the detector sub-combination.

#8 — US 4,591,272 A (Morris et al., Univ. of Michigan) — structurally closest apparatus.
Confirmed content: a first (argon) laser impinges on a TLC plate; a second (He-Ne) laser probes the gas phase directly above the point of impingement and is directed essentially parallel to the plate; deflection is sensed with a knife-edge/razor + photodiode (PMT alternative), i.e., the exact optical geometry recited in the patent. It even contemplates replacing the impinging laser with a pulsed laser and using gated integration.
Potentially anticipates: claims 7, 8, 16, 18, 20 (probe beam parallel to and spaced above a surface; knife-edge/PMT position sensing of beam deflection). Critical distinction: Morris heats the gas above a plate via photothermal absorption — it does not vaporize the material into a plume, so the "laser-generated plume of vaporized material" and "density gradient of the plume" limitations of claims 1/11/12 are not disclosed. Strong § 103 reference; weak § 102 reference for the independent claims.

#2 — US 4,468,136 A (Johns Hopkins). Optical beam-deflection thermal imaging: a probe beam is deflected by a thermally induced index gradient and the deflection imaged. Relevant to claims 8, 9, 12 (monitoring means), 18.

#3 — US 4,540,285 A and #7 — US 4,591,718 A (both U.S. DOE). Photothermal (beam-deflection) methods for determining calorific properties / in-situ composition of coal. Relevant to claims 1, 8, 12 for the generic "impose energy on a material, probe the resulting gradient optically" concept — but photothermal heating of a solid is a different physical event from laser vaporization into a plume.

#5, #9, #10, #11, #12 — Therma-Wave family; #6 — US 4,589,783 A (Wayne State). Thermal-wave generation and detection, and evaluation of surface/subsurface characteristics using probe beams. Collectively the closest field art for claims 12, 18, 19, 22 (non-destructive optical probing of surface-adjacent changes), but they detect thermal waves/reflectance changes, not refractive bending by a vapor plume.

#1 — US 4,299,494 A (ANVAR). Heat-transfer measurement by an optical beam technique. General background art for claims 12, 18.

#14 — US 4,790,664 A (Canon). Measuring optical properties. General background; no specific bearing on any single claim.

#4 — US 4,543,386 A (ICI). "Vinylidene chloride copolymer aqueous latex composition." This is facially unrelated to laser plumes, beam deflection or refractive-index gradients. It appears to be a stray/mis-listed citation in the record and in my assessment anticipates no claim. I flag it rather than rationalize it.

B. Non-patent citations (4 entries, 2 unique)

*NPL-1 — Potter, et al., "Measurement of the Electron Density Distribution in Plasmas from the Bending of a Gas Laser Beam," Journal of Physics E (GB), Vol. 5, No. 9 (Sept. 1972).*
This is the single most on-point non-patent reference. It discloses passing a gas laser beam through a spatially varying density field and deriving the density distribution from the bending (refraction) of the beam. That is the core physical method of claim 1 step (c) and of claims 8–10.
Potentially anticipates: claims 8, 9, 10 (and the detection step of claim 1) if "plume" were read broadly as a dense vapor/plasma region. Its weakness as § 102 art is that the probed medium is a plasma investigated per se, not a plume of material vaporized off a surface by a first energy source; the antecedent "laser-generated plume of vaporized material from a surface" is not disclosed. Best used as the § 103 reference showing that beam-bending measurement of density gradients was known.

NPL-2 — Jackson, et al., "Photothermal Deflection Spectroscopy and Detection," Applied Optics, Vol. 20, No. 8, pp. 1333–1344 (Apr. 15, 1981).
The foundational review of the "mirage effect"/photothermal deflection technique: a pump beam creates an index gradient in a medium which deflects a probe beam sensed by a position detector.
Potentially anticipates: claims 8, 9, 18 (probe-beam deflection sensed by a position-sensitive detector) as a generic technique. Does not disclose laser vaporization of a surface material into a plume.

(The record lists each NPL twice — once without and once with an asterisk — so the 4 entries reduce to the 2 unique documents above.)

4. Bottom line on anticipation

• No cited reference alone discloses all elements of independent claims 1, 11 or 12. Each cited item is missing at least one of: (i) generation of a plume of vaporized material from a surface by a first energy source; (ii) probing that plume with a second beam; (iii) deriving the density gradient of that plume, in a single pass, as a function of time.
• The strongest § 102 positions in the record are against the dependent detector claims — principally claims 8, 9, 18, 19 in view of US 4,784,494 A (Torres) and US 4,591,272 A (Morris et al.), and claims 8–10 in view of Potter et al. (1972). Claims 7, 16, 20 find close structural support in US 4,591,272 A alone.
• The strongest § 103 combinations would be: US 4,591,272 A (or US 4,784,494 A or Potter 1972) + US 4,540,285 A / US 4,591,718 A (laser/photothermal vaporization of a surface material), with Jackson 1981 and the Therma-Wave family supplying the position-sensing/thermal-wave routine elements.
• US 4,543,386 A is, on its face, irrelevant and appears to be a mis-listed citation.

5. Caveats and limitations of this analysis

1. I retrieved the citation record and the full text/claims of US 4,921,348 from the Google Patents record and the USPTO-linked PDF; the 14 patent citations are analyzed using their titles, dates, assignees and, for US 4,784,494 A and US 4,591,272 A, their full text. I did not obtain full claim text for US 4,299,494 A, US 4,468,136 A, US 4,540,285 A, US 4,543,386 A, US 4,579,463 A, US 4,589,783 A, US 4,591,718 A, US 4,632,561 A, US 4,634,290 A, US 4,636,088 A, US 4,750,822 A or US 4,790,664 A. Where I had only bibliographic data, I have said so; those characterizations are provisional and should be confirmed against the full documents before relying on them.
2. The fetched patent markup does not reliably preserve the Google Patents "cited by examiner" (*) vs. "cited by third party" (†) flags, so I have not asserted which references were examiner citations versus applicant/IDS submissions.
3. A § 102 anticipation conclusion under 35 U.S.C. § 102 requires every element of a claim, arranged as in the claim, to be disclosed in a single reference. Titles alone cannot establish that; the entries above marked "potentially anticipates" are candidate challenges requiring full-document verification.
4. Note for completeness: the patent's own enabling publication — Chen & Yeung, Analytical Chemistry 1988, 60(9), 864–868 ("A spatial and temporal probe for laser-generated plumes based on density gradients") — predates the 1989-01-26 filing but is the inventors' own work (published ~May 1988, i.e. less than one year before filing), so it is not § 102(a) "by others" art and is not § 102(b) art. It is relevant to enablement/priority, not anticipation.

I'll ground this analysis by verifying the prior-art references cited on the patent page.

Obviousness Analysis — US 4,921,348 (35 U.S.C. § 103)

Patent: US 4,921,348 A — "Method and means for a spatial and temporal probe for laser-generated plumes based on density gradients"
Inventors: Edward S. Yeung; Guoying Chen · Assignee: Iowa State University Research Foundation (ISURF)
App. No. 07/301,485 · Filed/Priority: 1989-01-26 · Granted: 1990-05-01
Status: Expired — fee lapse effective 1994-05-01 (per Google Patents legal events); government rights under DOE Contract W-7405-ENG-82.
Source: https://patents.google.com/patent/US4921348/en

Scope caveat: The references below are those listed in the "Patent Citations" (14 US patents) and "Non-Patent Citations" (4 items) sections of the granted patent. I verified the full text/abstract of US 4,590,272, US 4,468,136, US 4,540,285, US 4,784,494, US 4,589,783 and the Potter 1972 paper. For US 4,299,494, US 4,579,463, US 4,634,290, US 4,636,088, US 4,632,561, US 4,750,822, US 4,590,718, US 4,790,664 and US 4,543,386 I am relying on the titles and assignee data as reproduced on the patent page; I flag where my characterization is limited to that.

1. The claims at issue

Note that independent claim 1 recites only an "energy source," not a laser, and contains no vacuum, no position-sensitive-detector and no time-correlation limitation. It is the broadest and most vulnerable claim.

2. The prior art on the face of the patent, grouped by teaching

Group A — Photothermal/optical beam deflection ("mirage effect") detection of refractive-index gradients

• Jackson, Amer, Boccara & Fournier, "Photothermal Deflection Spectroscopy and Detection," Applied Optics 20(8):1333–1344 (Apr. 15, 1981) — the foundational PDS reference. Teaches a pump laser that creates a localized index-of-refraction gradient in the medium adjacent a surface, and a probe beam skimmed parallel to that surface whose deflection is detected to measure the gradient. This is the single most important reference for the "detect refraction as a function of a density gradient" element.
• US 4,590,272 (Morris et al., Univ. of Michigan) — https://patents.google.com/patent/[US4591272](/patent/US4591272) — pump argon laser + He-Ne probe beam directed parallel to the plate, knife-edge/razor + photodiode detection, lock-in demodulation; states detection limits in the picogram–nanogram range and that a pulsed laser with gated integration may replace the chopped CW source (col. 6–7 of the printed patent).
• US 4,540,285 (DOE) — https://patents.google.com/patent/[US4540285A](/patent/US4540285A)/en — pulsed pump light focused onto a sample surface; probe beam parallel and close to the surface; deflection measured with a quadrant position sensor; amplitude of the deflection and its phase lag relative to the pump pulse are used to derive sample properties (calorific value, porosity). This reference supplies dose, timing, position-sensor and "derive other information from the deflection signal" teachings.
• US 4,468,136 (Johns Hopkins) — https://www.freepatentsonline.com/[4468136](/patent/4468136).html — optical beam deflection thermal imaging; probe beam "skims said sample surface at a normal offset distance (Zo)" (claim 12); detecting means may be a knife-edge detector (claim 10) or an array of resolution elements yielding vectorial displacement (claim 11), including a silicon wafer position detector whose output voltage depends on where the beam strikes (claim 21).
• US 4,589,783 (Wayne State Univ.) — https://FreePatentsOnline.com/[4589783](/patent/4589783).html — "mirage effect thermal wave imaging": a first laser generates a heating beam, a second optical probe beam is deflected by the induced gradient, and AC deflection signals are converted, stored and displayed; explicitly discusses modulated/pulsed laser beams and closed gas cells.
• US 4,299,494 (ANVAR) — "Measurement of heat transfer between a specimen and an ambient medium"; US 4,579,463 / 4,634,290 / 4,636,088 / 4,632,561 / 4,750,822 (Therma-Wave); US 4,590,718 (DOE); US 4,790,664 (Canon) — all in the same optical-probe/thermal-wave family directed to measuring thermally induced changes in optical properties using an excitation beam and a monitored probe beam. US 4,543,386 (ICI, vinylidene chloride copolymer latex) is facially unrelated to the claimed subject matter and would not be relied upon by any competent challenger.

Group B — Gradient detection by probe-beam deflection (non-thermal)

• US 4,784,494 (Torres) — https://patents.google.com/patent/[US4784494A](/patent/US4784494A)/en — expressly teaches the governing relationship θ = (D/n)(dn/dx) for a light beam traversing a refractive-index gradient, and that "this deflection can be measured by measuring the position of the light beam on the position detector" (col. 3). Teaches laser or LED probe beams and PSD-based detection of gradients.

Group C — Plasma/plume density measurement by beam bending (non-patent)

• Potter, Falconer & Smith, "Measurement of the electron density distribution in plasmas from the bending of a gas laser beam," J. Phys. E: Sci. Instrum. 5(9):910–914 (Sept. 1972), DOI 10.1088/0022-3735/5/9/021 — "The electron density distribution in an axisymmetric plasma may be determined by measuring the deviation of a gas laser beam on passing through the plasma… the bending is closely proportional to the difference between the axially averaged electron density at the radius at which the beam enters the plasma, and at the radius at which it leaves." This is direct evidence that a probe laser bent by the density/refractive gradient of a hot, expanding, ionized plume was known and quantified 17 years before the filing date.

Group D — Admitted prior art in the specification itself
The Background section concedes: "The imposition of an energy source, such as a laser beam, to a surface, with subsequent vaporization of a material on the surface, is of active interest for analytical purposes. The vaporized material forms what is called a plume, which generally expands and travels upwardly and away from the surface." It also cites Irons, McWhirter & Peacock, J. Phys. B 5:1975–1987 (1972) for the low-pressure conical expansion of laser plumes. Under In re Kahn / MPEP 2144.03, applicant-admitted prior art is available for § 103.

3. Claim-by-claim mapping

4. The two strongest § 103 combinations

Combination I (primary): Potter 1972 + Jackson 1981 (or US 4,590,272 / US 4,540,285) + admitted laser-ablation plume generation

Rationale and motivation:

1. Same field / same problem. Both references are optical-beam-probing methods for measuring refractive-index gradients in a gas or plasma. In re Bigio / Wood analogous-art analysis raises no barrier: Potter is plasma diagnostics by probe-laser bending; Jackson and the DOE/Michigan patents are photothermal probe-beam deflection with an He-Ne probe. The patent's own field statement (Background, "Field of the Invention") is "analytical procedures regarding vaporization of materials by laser from a surface," which sits squarely between them.
2. Complete functional correspondence. Potter supplies every element of claim 1 except that its plasma is not expressly generated by ablating a solid surface: an energy source creates a plume; a gas laser beam passes through the plume; the bending of that beam is measured and is quantitatively proportional to the plume's radial density distribution. Jackson/Jackson-type references supply the specific instrumentation — probe beam parallel to the sample at a fixed offset, PSD or knife-edge detection, transient/time-resolved readout.
3. Reasonable expectation of success. Both the mirage-effect literature and Potter's paper use classical, well-understood optics (the paraxial approximation and the Gladstone–Dale relation, both invoked verbatim by the patent itself at cols. 6–8). A skilled artisan would expect the denser, more strongly ionized, more localized ablation plume to bend a probe beam more, not less. The patent's own numerical example (H = 0.05 cm, v = 13,900 cm/s, deflection on the order of a milliradian) is squarely within the regime the cited literature had already modeled and measured.
4. Design incentive. By 1989, photothermal deflection had demonstrated detection limits of 7.5 pg to ~1 ng (US 4,590,272 reports 7.5 pg for α-ionone; the Characterization of the photothermal deflection densitometer paper reports 1.3 ng). The patent asserts roughly 1 ng sensitivity. There was therefore a concrete, documented incentive to push a known gradient-sensing technique onto the plasmas/vapor plumes produced by the laser-ablation microanalysis techniques (LIBS, laser microprobe mass analysis) then in active use.
5. KSR "obvious to try." Placing the probe beam through the ablating plume rather than beside the heated spot is a predictable variation of a known parameter (the probe-beam offset/position), with a predictable result — KSR Int'l v. Teleflex, 550 U.S. 398 (2007); MPEP 2144.04.

Combination II (for claims 9–10, 12, 18–21, 22–23): Combination I + US 4,784,494 (Torres) and US 4,468,136 (Murphy)

• Torres supplies the explicit analytic bridge — θ = (D/n)(dn/dx) and "this deflection can be measured by measuring the position of the light beam on the position detector" — and teaches laser probes and PSDs.
• Murphy supplies the geometry ("probe beam skims said sample surface at a normal offset distance (Zo)") and the detector species that claims 18–21 recite (knife-edge detector, detector array, silicon wafer position detector).
• US 4,540,285 supplies the claim 22 limitation directly: it teaches that the amplitude and timing of the deflection relative to the excitation pulse are both measured and carry distinct information about the sample. Claim 22 ("density gradient … correlated to time") is therefore no more than the ordinary use of a time-resolved deflection signal.
• Claims 17 (vacuum chamber) and the PMT/bi-cell species (20, 21) are obvious design choices under MPEP 2144.03 — vacuum ablation/diagnostic cells were standard, the specification itself justifies vacuum by reference to Irons 1972's conical low-pressure expansion, and both PMTs and bi-cell/quadrant photodiodes were routine position-sensing devices in this exact art.

5. Counterarguments a defender of the patent would raise (and their weight)

1. Different gradient physics. The cited photothermal references measure an index gradient created by heat diffusion into an ambient fluid; the patent measures the density gradient of the ejected vapor/plume itself. This is a real distinction, but it is precisely why the Potter 1972 plasma-bending reference matters — it removes the "vapor plume" gap. Weight: moderate if Potter is unavailable; low if it is.
2. Speed/regime mismatch. Photothermal deflection art is overwhelmingly AC/lock-in based and assumes quasi-steady diffusion; the patent probes a sub-microsecond single-shot transient. This is the best nonobviousness argument. Its weakness is that US 4,590,272 itself contemplates a pulsed pump with gated integration, and US 4,540,285 measures the phase lag of the transient deflection — i.e., transient, time-resolved deflection detection was already in the art.
3. Unexpected results / teaching away. The specification asserts (cols. 8–9) that, "contrary to some reports [David et al., IEEE J. Quantum Electron. 1966] which imply that laser generated plumes have constant radial density distribution in laser interferometry, it has been discovered that laser-generated plumes have a positive density gradient towards the plume center," and that the plume is described by a radially linear density profile. If substantiated with data, this is a cognizable unexpected-results argument. But note the tension: the patent's own theory assumes a radially linear profile (assumption 6) rather than deriving it, and the discovery is arguably a property of the plume (a natural phenomenon) rather than of the claimed method.
4. Prosecution history. Every one of these references was before the examiner (the asterisked citations are examiner citations); the claims were allowed over them. Combined with the presumption of validity and the clear-and-convincing burden, this materially raises the practical bar for any § 103 challenge.
5. No secondary considerations of record. There is no evidence of long-felt need, failure of others, unexpected results, licensing or commercial success in the record. Absent that, KSR's "predictable variation" analysis operates without rebuttal.

One further note (not § 103): the "Similar Documents" list includes Chen et al. (1988), "A spatial and temporal probe for laser-generated plumes based on density gradients" — the inventors' own publication. Because it is the inventors' own work published less than one year before the 1989-01-26 filing, it would not be a § 102(b) statutory bar and would not be "by others" for § 102(a) purposes under pre-AIA law; it is therefore not usable as prior art against this patent. It is, however, a candid indication that the claimed subject matter was in the public domain shortly before filing.

6. Conclusion

• Claims 1–11 and 12–23 are, on the face of the cited art, vulnerable to § 103. The combination of Potter et al. 1972 (probe-laser bending by a plasma/plume density gradient) with Jackson et al. 1981 and/or US 4,590,272 / US 4,540,285 / US 4,468,136 (probe beam parallel to the surface, position-sensitive detection, time-resolved deflection) renders claim 1 — and, by direct extension, claims 2–10 and 11 — prima facie obvious. The motivation is supplied by the shared field, the shared mathematical model (Gladstone–Dale + paraxial equation), the documented ng–pg sensitivity already achieved in photothermal deflection, and the routine character of the remaining limitations.
• The dependent claims add nothing patentable. Claims 17 (vacuum cell), 20–21 (PMT / bi-cell) and 22–23 (time and amount-vaporized correlation) recite conventional design choices or results inherently obtained from the disclosed measurement, at most an obvious design choice under MPEP 2144.03.
• Confidence. My confidence that a combination of Potter + Jackson/US 4,590,272/US 4,540,285 establishes a prima facie § 103 case is moderate-to-high for claims 1–11, 12–16, 18–21. For claims 17 and 23 my confidence is lower: I could not verify a specific reference in the cited record that describes a sealed evacuated chamber with windows for both the ablating and probing beams, and claim 23's correlation to "total amount of matter vaporized" is a result-oriented limitation whose proof would likely require an inherency showing or reliance on the patent's own admitted theory tying deflection magnitude to N₀.
• Caveats. I have not verified the full text of US 4,299,494, US 4,579,463, US 4,634,290, US 4,636,088, US 4,632,561, US 4,750,822, US 4,590,718, US 4,790,664 or US 4,543,386; my characterizations of those rest on their titles and assignees as listed on the patent page. Any of them may supply additional or different teachings than I have assumed. This analysis is retrospective and hypothetical — the patent is expired, and the claims enjoy a presumption of validity that would require clear and convincing evidence to overcome.