Wavelength modulation spectroscopy with a pulsed quantum cascade laser
Bibliographic record
Abstract
A pulsed distributed feedback quantum cascade laser (QCL) operating near 957 cm-1 was employed in wavelength modulation mode for spectroscopic trace gas sensing applications. The laser was excited with short current pulses (5-10 ns) with < 2% duty cycle. The pulse amplitude was modulated with a linear sub-threshold current ramp at 20 Hz resulting in a ~ 2.5 cm-1 frequency scan, which is typically wider than what has been reported for these lasers, and would allow one to detect molecular absorption features with line widths up to 1 cm-1. A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We then superimposed a sine wave current modulation at 10 kHz onto the 20 Hz current ramp. The resulting high frequency temperature modulation of the distributed feedback (DFB) structure results in wavelength modulation (WM). The set-up was tested by recording relatively weak absorption lines of carbon dioxide. We demonstrated a minimum detectable absorbance of 10-5 for this spectrometer. Basic instrument performance and optimization of the experimental parameters for sensitivity improvement 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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".