REVIEW 4 major objections 5 minor 12 references
Ultrafast pulsed laser evaluation of Single Event Transients in opto-couplers
T0 review · 4 major / 5 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read The paper claims the first laser-based single-event transient evaluation of the 4N35 optocoupler, with threshold at or below 0.07 MeV·cm²/mg and saturation at 1.17 MeV·cm²/mg—though no transients were actually seen.
desk verdict The abstract says SETs were observed, but the results say no transient pulses were seen; the central claim collapses, though the facility work is a usable starting point. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the equivalent-LET conversion: the number of electron-hole pairs produced in a sensitive volume of depth $d$ by a laser of power $y$ is set equal to the number produced by an ion of LET $c$, so laser power can be plotted as radiation dose. The paper applies this conversion to voltage-versus-power measurements on the base-collector junction of the decapped 4N35's silicon phototransistor, with the LED off and the base floating, so the collector current is purely photocurrent. The 10 ps, 1064 nm fiber laser focused to a ~1 μm spot is the enabling tool, chosen because pico-second pulse times match the interaction timescale of an ionizing particle in the semiconductor.
What would settle it
Measure the same decapped 4N35 under a heavy-ion beam with known LET and compare the collector-emitter voltage response with the laser-derived curve; if the ion response does not reproduce the $0.07$ and $1.17\,\mathrm{MeV\,cm^2/mg}$ breakpoints, the equivalent-LET conversion is wrong. Alternatively, repeat the laser experiment with a chopper or a low-repetition-rate source to resolve individual transients; if no transient appears near the claimed threshold, the SET claim fails.
Extended reading notes
Core claim
On the authors' own terms, the central discovery is that a 10 ps pulsed laser can be used to probe the charge-collection response of a 4N35 optocoupler and convert that response into equivalent LET values. Stripping the ceramic cap exposes the silicon phototransistor, and varying the focused laser power produces a collector-emitter voltage curve that saturates at an equivalent LET of $1.17\,\mathrm{MeV\,cm^2/mg}$; the threshold for a detectable response is claimed to be $\leq 0.07\,\mathrm{MeV\,cm^2/mg}$. The same section reports that no transient pulses were observed across the collector-emitter junction, which the authors attribute to the mismatch between the 20 MHz laser repetition rate and the slow response of the 4N35. The paper therefore claims the first laser-based SET evaluation of this part, with the caveat that the observable was the DC voltage response rather than resolved transients.
Load-bearing premise
The conversion from laser power to equivalent LET assumes that equal electron-hole pair generation occurs for lasers and ions in a sensitive volume of depth $d$, but $d$ is never specified and the conversion is never calibrated against a known radiation source.
Editorial extensions
If this is right
- If the values hold, 4N35 users get screening numbers from a benchtop laser: an SET threshold at or below $0.07\,\mathrm{MeV\,cm^2/mg}$ and saturation at $1.17\,\mathrm{MeV\,cm^2/mg}$.
- A pico-second laser facility built from a fiber laser and a lensed pigtail can substitute for accelerator access in initial optocoupler radiation screening.
- Because the 4N35 responds on a timescale near $50\,\mu\mathrm{s}$, individual transients require a low-repetition-rate laser or a chopper; the 20 MHz system can only bound the device's response.
- The observed DC saturation behavior, if correctly converted, gives a fast testable prediction: transients, once resolved, should grow in width with LET and saturate near the recombination time.
Reading between the lines
- Because the paper reports no observed transient pulses, the threshold and saturation numbers are extrapolations from DC photoresponse, not measured SET events; the "first laser SET evaluation" is really a first static charge-collection characterization.
- The equivalent-LET calibration is unverified, so the quoted numbers should be treated as order-of-magnitude; a small error in the assumed sensitive depth $d$ changes both values proportionally.
- A natural extension would be to gate the laser output or lower its repetition rate to catch individual transients and compare their widths with the claimed LET curve; if the pulse widths track the saturation curve, the conversion gains confidence.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper describes the construction of a 1064 nm, 10 ps pulsed laser facility for single-event transient (SET) testing and reports its application to a 4N35 optocoupler. The authors claim that this is the first laser-based observation of SETs in the 4N35, with a threshold equivalent LET of at most 0.07 MeV.cm2/mg and a saturation equivalent LET of 1.17 MeV.cm2/mg. However, Section 3 explicitly states that no transient pulses were observed in the collector-emitter voltage; the reported values are based on DC voltage shifts as laser power is varied. The equivalent-LET conversion is asserted without a derivation, the sensitive volume depth d is never specified, and no error analysis is provided.
Significance. If the central claim were valid, a low-cost, tabletop laser-based screening method for SETs in optocouplers would be of practical value to radiation-effects testing. The paper does provide a useful description of a compact experimental setup, including the de-capping procedure and the lensed fiber focusing arrangement, and the reported DC photoresponse data may have limited screening utility. However, the paper's main scientific claim is not supported by the data: no SET was observed, and the LET values are ungrounded because the conversion from laser power to LET is neither derived nor calibrated. The work therefore does not, as it stands, demonstrate the claimed first laser-based SET evaluation of the 4N35.
major comments (4)
- [Section 3 (also Abstract and Conclusion)] The central claim that SETs in the 4N35 were observed is contradicted by the paper's own statement in Section 3: 'In our experiment, we could not observe transient pulses for collector-emitter voltage.' A SET is, by definition, a transient voltage or current pulse induced by a single ionizing particle, so if no transient pulse was recorded, no SET was observed. The reported threshold (≤0.07 MeV.cm2/mg) and saturation (1.17 MeV.cm2/mg) values are therefore derived from DC photoresponse measurements, not from SET measurements, and the title, abstract, and conclusion overstate what the data support.
- [Section 3, equivalent-LET equation] The conversion from laser power to equivalent LET is asserted, not derived. The equation as printed equates unspecified quantities and never defines the sensitive volume depth d; the paper also provides no calibration against ion-beam data and no error or uncertainty analysis. Consequently, the numerical LET values quoted in the text and plotted in Figure 2 are ungrounded, even when interpreted only as DC-response thresholds.
- [Section 3, repetition-rate discussion] The paper's own explanation that the 20 MHz laser repetition rate is much higher than the 4N35 response time (with a recombination time quoted as ~50 µs) confirms that the measurement configuration could not resolve individual transients. The further statement that the maximum transient pulse width at saturation would equal the recombination time is speculative and is not a measured quantity; it does not rescue the claim that SETs were observed.
- [Abstract and Conclusion] The claim that this is the 'first report demonstrating the laser-based evaluation of SETs in the 4N35 optocoupler' is not supported, because the experiment did not observe SETs. At most, the paper reports a DC photoresponse characterization under pulsed illumination. Since reference [2] also reported no SETs for this part in accelerator testing, the present null result is consistent with prior data, but the framing as a first observation of SETs is misleading.
minor comments (5)
- [Section 2] The phrase 'TH pigtail fiber' appears to be a typo and should read 'The pigtail fiber'; the manuscript would benefit from a full proofreading pass.
- [Section 3, Figure 2] Figure 2(b) and 2(c) plot 'VCE vs. LET' and 'VR vs. LET', but the measurements are DC or quasi-DC voltage changes, not transient responses; the axis labels and captions should make this distinction clear.
- [Section 3, equation] The equivalent-LET equation is not typeset correctly and contains undefined variables ('e-h', 'y watt', 'c'); a clean, explicitly defined equation is needed, even if the conversion is only a working assumption.
- [Throughout] No measurement uncertainty or repeatability data are reported for the voltage or LET values; at minimum, the authors should state the number of devices tested and the observed run-to-run variation.
- [References] Reference [5] is given as a datasheet URL without an access date or document number, and reference [7] is cited but not discussed in the text; the reference list should be formatted consistently.
Circularity Check
No circularity: the LET conversion is an uncalibrated external assumption, and the absence of observed transients is a correctness issue, not a circular derivation.
full rationale
The paper's derivation chain is not circular. The reported equivalent-LET values are computed from laser-power measurements through an explicit conversion formula that assumes equal electron-hole pair generation by ions and lasers in a sensitive volume of depth d. That assumption is an external modeling choice, not an input that already contains the reported threshold or saturation values. The threshold and saturation LET values are inferred from the laser-power scan, not defined in terms of the final claims. No parameter is fitted to the target result and then renamed as a prediction. The authors cite no prior work of their own to justify a load-bearing premise, and the invoked references are independent published data or datasheets. The most serious problem in the paper is not circularity: Section 3 states 'In our experiment, we could not observe transient pulses for collector-emitter voltage,' which contradicts the abstract's claim of observing SETs and undermines the threshold-LET statement, but a contradiction between a claim and the reported data is a correctness or evidentiary failure, not a circular reduction. Similarly, the unstated depth d and lack of calibration make the absolute LET numbers uncertain, but uncertainty in a modeling assumption is not circularity. Under the stated hard rules, a self-contained measurement with an external, unverified assumption receives a low circularity score; here that score is 0.
Assumptions & free parameters
free parameters (2)
- Sensitive volume depth d
- Laser-to-LET conversion factor
assumptions (4)
- domain assumption The number of electron-hole pairs generated by the laser equals the number generated by an ion of equivalent LET in the sensitive volume.
- domain assumption The base-collector junction is the active region and the base current consists solely of photocurrent.
- domain assumption Decapping and removing the optical gel does not alter the device's response.
- domain assumption 1064 nm light is absorbed in the silicon depletion region in a way comparable to ionizing particles.
Cite this review
Pith. "Pith review of Ultrafast pulsed laser evaluation of Single Event Transients in opto-couplers." pith.science (2026). https://pith.science/paper/OEXKZRRL
@misc{pith2026250107590,
author = {Pith},
title = {Pith review of: Ultrafast pulsed laser evaluation of Single Event Transients in opto-couplers},
year = {2026},
howpublished = {\url{https://pith.science/paper/OEXKZRRL}},
note = {Machine review of arXiv:2501.07590}
}
read the original abstract
We build a 1064 nm fiber laser system-based testing facility for emulating SETs in different electronics components and ICs. Using these facilities, we tested the 4N35 optocoupler to observe SETs for the first time.
Reference graph
Works this paper leans on
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[2]
Using these facilities, we tested the 4N35 optocoupler to observe SETs for the first time
Space Applications Center, Indian Space Research Organization, Ahmedabad, India E-mail: kavindave22@gmail.com* Abstract: We build a 1064 nm fiber laser system-based testing facility for emulating SETs in different electronics components and ICs. Using these facilities, we tested the 4N35 optocoupler to observe SETs for the first time. © 2022 The Author(s)
work page 2022
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[1]
Introduction Optocouplers (also known as optoisolators) are used for switching and isolating high and low -voltage circuits. These features make them suitable for consumer electronics to space vehicles spaceflights, satellites, and planetary rovers. The basic build design of optocouplers involves a light source and a photosensitive detector placed in clos...
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[3]
Experimental set-up We built an in-house laser testing system at IIT Bombay using a commercially available 10 picosecond 106 4 nm laser with a pulse repetition rate of 20 MHz. TH pigtail fiber of the laser has a lens on its face, ensuring the spot size of the light is 1 μm at the focus point. In this experiment, we tested commercially available 4N35 optoc...
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[4]
Results and Discussion In absence of any light, there is only a thermal current flowing across the collector-emitter junction, called the dark current. When light falls on this collector-base junction, photons are absorbed in the depletion region, forming free electron-hole pairs which move under the influence of applied potential between collector and em...
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[5]
Conclusion We have set up a 1064 nm laser-based testing facility for emulating SETs effects in electronics components and ICs. We have miniaturized the set-up by employing a lensed fiber patch cord ensuring the ~1 μm spot size at its focal point. To the best of our knowledge, this is the first report demonstrating the laser-based evaluation of SETs in the...
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[6]
R.A. Reed et al., “Emerging Optocoupler Issues with Energetic Particle-Induced Transients and Permanent Radiation Degradation” IEEE Trans Nucl Sci, Vol 45, No. 6, December 1998
work page 1998
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[7]
A compendium of recentoptocoupler radiation test data,
K.A. LaBel et al. “A compendium of recentoptocoupler radiation test data,”. IEEE Radiation Effects DataWorkshop:123-146, July 2000
work page 2000
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[8]
Pulsed Laser Evaluation of Single Event Transients in Optocouplers
Ma Yingqi, “Pulsed Laser Evaluation of Single Event Transients in Optocouplers”, Tencon 2009, Beijing, China
work page 2009
Show all 12 references
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[9]
Pulsed Laser Testing for Single Event Effects Investigation
S. P. Buchner et al. , “Pulsed Laser Testing for Single Event Effects Investigation”, IEEE Trans Nucl Sci, Vol 60, No. 3, June 2013
2013
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[10]
Datasheet, 4N35, Vishay Semiconductors, https://www.vishay.com/doc/?81181=
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[11]
Single Event Upset Effects in Optocouplers
A.H. Johnston et al., “Single Event Upset Effects in Optocouplers ”, IEEE Trans Nucl Sci, Vol 45, No. 6, December 1998
1998
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[12]
Linear Energy Transfer of Heavy Ions in Silicon
A.Javanainen et al., “Linear Energy Transfer of Heavy Ions in Silicon”, IEEE Trans Nucl Sci, Vol 54, No. 4, August 2007
2007
Reviewed August 10, 2026 · model on record in the stance chip above.
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