{"id":"3cd882e2-4685-4ce0-b457-68dc79dc763f","arxiv_id":"2507.22866","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Two commercial beamsplitter coatings, a 22-layer Ta2O5/SiO2 stack and a 5-layer SiOx/SiO2 stack, come close to equal reflectivity and phase for both polarisations but not both at 45 degrees.","lead":"Two vendor-built beamsplitter coatings were measured to see if they split light evenly and shift both polarisations equally, a requirement for future gravitational-wave speedmeters. Both come close, but neither fully meets the target at the standard 45-degree angle.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Abstract and body disagree on the key numbers (46° vs 47°, 49/51 s/p swapped, 5° vs 7° phase), so the central quantitative claims are not yet consistently supported.","rationale":"The reader's verdict is CONDITIONAL and I agree with that disposition. My reason for focusing on the abstract/body numerical conflicts rather than the common-mode offset is that the offset is at least explicitly characterized ('without large variations'), whereas the manuscript never reconciles 46° vs 47°, the reversed s/p assignment, or 5° vs 7°. These are not subtle statistical concerns; they are contradictions in the advertised quantitative results. Because no raw data are provided, a reader cannot determine which figures of merit are correct. This directly affects the central claim, which is a list of measured numbers. The proposed check is practical: it requires only the underlying datasets or digitization of the two figures, and it would establish whether the abstract or Section II B is correct. If the body values are correct, the abstract's specific numbers (46°, 49%/51% s/p, 5°, 44.25°) need correction before the paper can be used as a reference for coating specifications. The qualitative conclusion — that two vendors produced coatings close to, but not meeting, all-polarisation behaviour — is likely robust, so rejection is not warranted; a conditional accept with a data-release and consistency-check requirement is appropriate.","tokens_in":10846,"tokens_out":7713,"duration_ms":90231,"concrete_test":"Obtain the per-sample datasets behind Figs. 6 and 10 (or digitize the figures) and recompute: (i) the crossing angle of the Laseroptik s/p reflectance curves for each plane sample, the Optoman mean s/p reflectances at 45°, and the mean Optoman differential phase over the angular range; (ii) the zero-phase crossing for each Laseroptik phase curve, with and without the −1.75° offset. If the recomputed values agree with Section II B (47°; 51% s / 49% p) and with an offset-dependent crossing, then the abstract's 46°, swapped s/p, and 44.25° values are unsupported and must be corrected.","verdict_should_be":"UNCHANGED","load_bearing_attack":"To establish the central claim, the quoted values — Laseroptik equal reflectivity 51% at 46°, zero differential phase at 44.25°; Optoman 49/51 and ~5° — must be unambiguous. They are not. Section II B states the Laseroptik equal-reflectance condition is met 'close to 47°' for plane samples, not 46° as in the abstract, and reports Optoman average reflectances of '∼51% for s-polarised light and ∼49% for p-polarised light', the reverse of the abstract's 49%/51%. The 44.25° zero-phase crossing appears only in the abstract; Section III C quotes Optoman as having a 'dark fringe offset of Δφbs ∼ 7°' whereas the abstract says 'around 5°'. Since no raw data or per-sample tables are given, the manuscript itself cannot resolve which set of numbers is correct. The paper also acknowledges systematic phase variations below 1.5° and a −1.75° common-mode offset (Section II C) without propagating these into the headline angles. The qualitative claim may survive, but the specific numbers that would be cited are internally inconsistent.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper characterizes two commercial beamsplitter coatings, from Laseroptik and Optoman, that were ordered on a best-effort basis to have similar optical properties for s- and p-polarised light, as required for polarisation-based speedmeter interferometers. The authors use SEM/EDX to determine coating structure, a photodiode-based setup to measure power reflectance versus angle of incidence, and a scanning Michelson interferometer with multiple phase-estimation methods to measure the differential phase shift between polarisations. They report that the Laseroptik 22-layer Ta2O5/SiO2 coating achieves equal power reflectivity near 51% and a zero differential phase, while the thinner 5-layer Optoman SiO2/SiOx coating achieves near-50/50 reflectance with a small, angle-insensitive phase shift. The qualitative conclusion is that industrial coatings can approach the all-polarisation beamsplitter specification, but the quantitative claims are currently inconsistent between the abstract and the body.","tokens_in":11078,"tokens_out":4083,"duration_ms":49041,"significance":"If the quantitative claims survive revision, this is a useful and timely experimental contribution: there are few published characterisations of industrially fabricated coatings that approach polarisation-symmetric beam-splitting behaviour, and the connection to polarisation-based speedmeters is relevant for future gravitational-wave detectors. The measurement methodology is a strong point: the paper describes multiple independent phase-estimation methods (Pearson correlation, cross-correlation, Lissajous ellipse fitting), cross-checks statistical uncertainties with Monte Carlo and bootstrap resampling, and uses repeated measurements and sample-to-sample scatter to estimate systematic errors. The SEM/EDX structural analysis is also clearly presented and supports the claimed difference in coating design strategies. However, the paper in its current form does not support the specific headline numbers because the abstract and the body disagree on several of them.","major_comments":[{"comment":"The central Laseroptik result is internally inconsistent: the abstract states 'equal power reflectivity of 51% at 46 deg angle of incidence', while Section II B states that for the plane beamsplitter samples (LO-P) the equal-reflectance condition is met 'close to 47 deg at 51% reflectance'. The measurement grid in Section II B uses 0.5° steps, so 46° and 47° are not interchangeable without showing the data or the interpolation procedure. No raw data or per-sample tables are provided, so a reader cannot determine which number is correct. Please harmonise the abstract with the body and provide the underlying data or an explicit statement of how the equality angle was obtained.","section":"Abstract; Section II B"},{"comment":"The Optoman reflectivity values are reversed between abstract and body. The abstract reports '49% for s-polarisation and 51% for p-polarisation', whereas Section II B states that the averaged reflectance is '~51% for s-polarised light and ~49% for p-polarised light'. Since the paper's key claim concerns the magnitude and sign of |Rp - Rs|, this is a material discrepancy that must be corrected before the results can be cited.","section":"Abstract; Section II B"},{"comment":"The reported differential phase values for the two coatings are not consistent within the manuscript. The abstract quotes the Optoman differential phase as 'around 5 deg', while Section III states a 'dark fringe offset of Δφbs ∼ 7°'; given the quoted measurement-to-measurement standard deviation of less than 1.5° (Section II C), these values are not compatible at the stated precision. In addition, the Laseroptik zero-phase crossing at 44.25° appears only in the abstract; the body (Section III) states only that the zero-phase condition is reached 'for a smaller angle of incidence compared to the target 45°'. Please make the reported values consistent and specify which samples and data sets produce each headline number.","section":"Abstract; Section III"},{"comment":"The common-mode phase offset of -1.75°, measured with only p- or s-polarised light, is subtracted from all phase-shift data, but its uncertainty and any possible dependence on sample or angle are not propagated into the reported zero-crossing angle or residual phase values. The text says there were 'no large variations' but gives no quantitative bound. Given that the quoted systematic uncertainty from repeated measurements is already 1.5°, this offset should be treated as a systematic error and propagated before the headline phase results are considered established.","section":"Section II C"}],"minor_comments":[{"comment":"The definition of SiOx is internally inconsistent: the introduction and Section II A define the material as SiOx with 0 < x < 2, but the text later says 'SiO_x is either amorphous silicon (x = 0) or substoichiometric silicon oxide (0 < x < 2)'. Since x = 0 falls outside the earlier range, please reconcile the definition.","section":"Section II A"},{"comment":"The word 'introcuded' in the caption of Fig. 7 should be 'introduced'.","section":"Fig. 7 caption"},{"comment":"Equation (1) defines reflectance as R = PR/(PR + PT), which assumes negligible absorption and scattering. A sentence stating whether losses were checked to be negligible would strengthen the interpretation of the reported reflectance values.","section":"Section II B"}],"recommendation":"major_revision","confidential_remarks":"The paper fits the journal's scope and the measurement methodology is careful, but the abstract/body inconsistencies suggest a versioning error that must be fixed before publication. I am not recommending rejection: the qualitative claims are plausible and the experimental effort is substantial. The authors should be asked to supply the raw data or a data table for the headline numbers so that the discrepancies can be resolved, and to propagate the common-mode offset uncertainty."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a legit experimental paper — two industrial coating designs characterized for polarization-symmetric beamsplitting, with a careful phase-measurement chain. The qualitative message, that neither coating fully meets the all-polarisation specification at 45° but both get close in different ways, is probably right. But the abstract and the body disagree on several of the numbers that would actually be cited, and that has to be fixed before anyone should rely on it.\n\nWhat's new: the SEM/EDX decomposition of the actual layer stacks (22-layer Ta2O5/SiO2 vs 5-layer SiO2/SiOx) is a useful piece of reverse-engineering, and the direct comparison of the two vendor strategies on the same measurement bench is not in the literature. The phase extraction is done carefully — Pearson, cross-correlation, ellipse fitting, plus Monte-Carlo and bootstrap checks — and they are upfront that sample-to-sample variation dominates, at <1.5°. That is honest experimental practice.\n\nSoft spots: the numbers. The abstract says Laseroptik reaches equal reflectance at 46°, the body says close to 47° for plane samples. For Optoman, abstract says 49% s / 51% p; body says ~51% s / ~49% p — swapped. And the differential phase: abstract says ~5°, Section III says ~7°. The zero-phase crossing at 44.25° appears only in the abstract. The stress-test note is right: the manuscript itself cannot resolve which set is correct. Also, the −1.75° common-mode offset is subtracted from all phase data but there is no analysis of how much it might vary across samples/angles; given the claimed zero-crossing angle is derived from those shifted curves, that matters. No raw data or per-sample tables are included, so the inconsistencies can't be checked externally.\n\nProportion: none of this kills the qualitative conclusion. The defects are in reporting, not in the measurement concept. But the paper is being submitted for a component that people will want to quote by number, and the current numbers are not stable.\n\nRecommendation: worth peer review, but only after a revision that reconciles abstract and body, propagates uncertainties into the headline angles, and ideally makes the dataset available. I'd send it to a serious referee who works on coatings or GW interferometry. For my own work, I wouldn't cite the numbers yet.","headline":"A careful, useful coating characterization whose headline numbers are not yet consistent between abstract and body — fix the numbers and release data, and it's a solid contribution.","tokens_in":11640,"tokens_out":2276,"would_cite":false,"duration_ms":24754,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["42.79.Fm","07.60.Ly","04.80.Nn"],"model":"deepseek-v4-flash","headline":"Two industrially fabricated beamsplitter coatings approach the polarisation-symmetric reflection and phase needed for polarisation-based speedmeters in gravitational-wave detectors.","keywords":["all-polarisation beamsplitter","polarisation-based speedmeter","gravitational-wave interferometer","differential phase shift","multilayer dielectric coating","Ta2O5/SiO2","SiO2/SiOx","scanning Michelson interferometer"],"falsifier":"Measure the differential phase of a Laseroptik sample at 44.25 degrees incidence with an independent technique that does not rely on subtracting the common-mode offset, for example spectroscopic ellipsometry or a dual-wavelength interferometer; if the zero-crossing angle moves by more than the roughly 1.5 degree sample-to-sample variation, the common-mode offset assumption is wrong.","tokens_in":10676,"feed_emoji":"🔭","tokens_out":9008,"duration_ms":87940,"temperature":0.7,"pith_summary":"This paper tries to establish that commercially obtainable dielectric beamsplitter coatings can come close to treating s- and p-polarised light identically, the property a polarisation-based speedmeter needs to reduce back-action noise in gravitational-wave interferometers. It characterises two best-effort coatings, one from Laseroptik and one from Optoman, at 1550 nm. The Laseroptik coating, a 22-layer Ta2O5/SiO2 stack, reaches equal power reflectivity of 51% at 46 degrees incidence and zero differential phase at 44.25 degrees. The Optoman coating, a 5-layer SiO2/SiOx stack, holds reflectivity near 49%/51% and a differential phase of about 5 degrees across the measured angle range. If the results hold, the remaining task is to re-optimise the designs so that equal splitting and zero phase occur together at the 45-degree working angle.","feed_headline":"Two coatings nearly meet the all-polarisation beamsplitter spec","feed_subtitle":"The optics polarisation-based speedmeters need to cut back-action noise in gravitational-wave detectors.","key_machinery":"The argument is carried by two multilayer coating stacks and two optical setups. The Laseroptik stack is 22 alternating Ta2O5/SiO2 layers about 5 micrometres thick; the Optoman stack is 5 layers of SiO2 and SiOx about 0.4 to 0.5 micrometres thick. Power splitting is measured from reflected and transmitted powers at 1550 nm over a +-2 degree range around 45 degrees incidence, using R = PR/(PR+PT) to remove sensitivity to power fluctuations. Differential phase is measured in a scanning Michelson interferometer: the p- and s-polarisation outputs form fringe signals, and the phase between them is recovered by Pearson correlation and Lissajous-ellipse fitting. A -1.75 degree offset, measured with single-polarisation light, is subtracted as a common-mode phase from all datasets.","core_discovery":"The paper reports the characterisation of two best-effort all-polarisation beamsplitter coatings. A 22-layer Ta2O5/SiO2 coating from Laseroptik achieves equal power reflectivity of 51% for s- and p-polarisation at 46 degrees angle of incidence and zero differential phase shift at 44.25 degrees. A 5-layer SiO2/SiOx coating from Optoman achieves power reflectivities of 49% for s-polarisation and 51% for p-polarisation, with a differential phase shift of about 5 degrees that is largely independent of angle of incidence. Both are measured at 1550 nm and compared with an off-the-shelf s-optimised beamsplitter, and the layer structures are reconstructed with SEM and EDX. The paper concludes that the two design goals for all-polarisation beamsplitters, polarisation-independent power splitting and polarisation-independent phase, are approachable with existing industrial coating technology, although neither coating meets both goals at the target 45-degree angle.","pith_inferences":["If the -1.75 degree common-mode offset is not truly constant across samples and angles, the reported zero-crossing angle of 44.25 degrees for Laseroptik and the roughly 5-degree residual for Optoman could shift by more than the stated uncertainties; an independent phase measurement that avoids this subtraction would settle it.","A natural next step is to use the reconstructed layer thicknesses to simulate both coatings and invert the design problem, asking which thickness changes would put equal reflectivity and zero phase at 45 degrees; the Laseroptik stack's 22 layers make this a plausible optimisation.","The angle-independent phase of the Optoman coating suggests a single birefringent phase plate placed after the beamsplitter could null the 5-degree shift over the whole angular range, a cheap fix worth testing.","The paper's approach could also qualify coatings for space-based or optical-communication polarisation-symmetric beamsplitters where angular tolerance matters."],"forward_implications":["The Laseroptik 22-layer design has enough free parameters that a re-optimisation could bring the equal-reflectivity and zero-phase points together at 45 degrees, provided deposition tolerances are controlled.","The Optoman design's angle-insensitive phase means that, once the residual roughly 5-degree shift is compensated, the coating could tolerate larger alignment errors than the Laseroptik design.","Residual differential phase can be handled at the interferometer level by a phase plate or temperature control, or by operating away from 45 degrees and compensating with intermediate telescopes planned for future detectors.","The characterisation method, power-ratio measurement plus scanning Michelson with Lissajous phase readout, applies directly to other beamsplitter coatings for polarisation-symmetric interferometry."],"supporting_citations":[{"why":"Introduces the speedmeter concept that motivates the need for polarisation-symmetric beamsplitters.","marker":"[7]"},{"why":"Reviews quantum noise in interferometers, establishing the back-action limit that speedmeters aim to beat.","marker":"[6]"},{"why":"Shows that a graded-index film can yield similar properties for p- and s-polarisation, a design precedent the paper builds on.","marker":"[14]"},{"why":"Demonstrates that using more than two coating materials can produce polarisation-insensitive coatings.","marker":"[15]"},{"why":"Used to identify the Optoman sub-stoichiometric SiOx layers as amorphous or partially oxidised silicon.","marker":"[22]"},{"why":"Provides the Pearson correlation coefficient used to estimate the phase shift between the two polarisation fringe signals.","marker":"[23]"},{"why":"Supplies the least-squares ellipse fitting method used to extract the phase shift and its sign from the Lissajous figure.","marker":"[24]"}],"fun_headline_variants":["Polarisation-independent beamsplitters closer to reality","Two coatings inch toward all-polarisation beamsplitters","Beamsplitters for gravitational-wave speedmeters pass tests","All-polarisation beamsplitter: two designs, one spec gap"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"A -1.75 degree phase offset, measured once with only p- or s-polarised light, is assumed to be the same for every sample and every angle and is subtracted from all phase measurements; if it changes with sample or angle, the reported zero-crossing and residual phases shift accordingly.","fun_headline_variants_meta":{"raw":{"variants":["Polarisation-independent beamsplitters closer to reality","Two coatings inch toward all-polarisation beamsplitters","Beamsplitters for gravitational-wave speedmeters pass tests","All-polarisation beamsplitter: two designs, one spec gap"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000245,"raw_usage":{"total_tokens":1536,"prompt_tokens":943,"completion_tokens":593,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":559,"completion_tokens_details":{"reasoning_tokens":538}},"tokens_in":559,"tokens_out":593,"duration_ms":6706,"temperature":1.0,"reasoning_tokens":538,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T11:12:28.992419+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the differential phase of a Laseroptik sample at 44.25 degrees incidence with an independent technique that does not rely on subtracting the common-mode offset, for example spectroscopic ellipsometry or a dual-wavelength interferometer; if the zero-crossing angle moves by more than the roughly 1.5 degree sample-to-sample variation, the common-mode offset assumption is wrong.","supporting_citations":[{"cited_title":"Braginsky and F","cited_arxiv_id":null,"evidence_quote":"Introduces the speedmeter concept that motivates the need for polarisation-symmetric beamsplitters."},{"cited_title":"Danilishin, F","cited_arxiv_id":null,"evidence_quote":"Reviews quantum noise in interferometers, establishing the back-action limit that speedmeters aim to beat."},{"cited_title":"Zukic, K","cited_arxiv_id":null,"evidence_quote":"Shows that a graded-index film can yield similar properties for p- and s-polarisation, a design precedent the paper builds on."},{"cited_title":"Mordechai, Applied Optics 31, 5345 (1992)","cited_arxiv_id":null,"evidence_quote":"Demonstrates that using more than two coating materials can produce polarisation-insensitive coatings."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Used to identify the Optoman sub-stoichiometric SiOx layers as amorphous or partially oxidised silicon."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the Pearson correlation coefficient used to estimate the phase shift between the two polarisation fringe signals."},{"cited_title":"Halir and J","cited_arxiv_id":null,"evidence_quote":"Supplies the least-squares ellipse fitting method used to extract the phase shift and its sign from the Lissajous figure."}],"review_version":1}