Open path spectroscopy of methane using a battery operated vertical cavity surface-emitting laser system
Bibliographic record
Abstract
Tunable diode laser spectroscopy (TDLS) is a well-established method for trace gas detection. TDLS systems usually employ edge-emitting diodes with a distributed feedback configuration. Recently long wavelength vertical cavity surface emitting lasers (VCSEL) have emerged as an alternative source for spectroscopic applications. The relatively low cost, low power requirements and large tuning range of VCSELs make them particularly attractive for portable gas detection systems. In this paper we describe a battery-operated VCSEL spectroscopy system operating near 1650 nm for methane detection. Wavelength modulation spectroscopy (WMS) is commonly used in TDLS systems to improve sensitivity. WMS in these systems is usually implemented with a hardware based lock-in amplifier. We report on the construction of a new system with software WMS and compare its operation with a conventional system. The VCSEL TDLS system is used to probe the 2v3 band of methane over an open path. The relative contributions of optical and electrical noise to the system signal to noise ratio and minimum gas detection level is presented. Finally, challenges and future design considerations in VCSEL spectroscopy are discussed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".