Quantum-limited laser frequency-modulation spectroscopy (original) (raw)
Laser FM spectroscopy with photochemical modulation
Applied physics, 1984
We have combined the techniques of frequency-modulation spectroscopy (FMS) and photochemical-modulation spectroscopy to carry out high-resolution, high-sensitivity absorption measurements on the formyl and amino radicals. Using the (0, 9 ~ 0)-(0, 01, 0) band of the A, 2A"-)~, 2A' transition of HCO at 614 nm, we obtained a sensitivity limit for absorption of 1.5 x 10-6. Reconstructed spectra of several HCO lines are presented.
High-sensitivity frequency-modulation spectroscopy with a GaAlAs diode laser
Journal of the Optical Society of America B, 1989
A high-sensitivity spectroscopic system has been constructed with a GaAlAs diode laser by using two-tone frequency-modulation spectroscopy. We have demonstrated an absorption sensitivity of 3 X 10-7 in a 0.84-Hz bandwidth by using the Doppler-broadened water vapor absorption line at 12 238.32 cm-'. The sensitivity is limited by laser excess noise and is approximately five times less than the sensitivity expected on the basis of detector noise.
Frequency-modulation spectroscopy with transform-limited nanosecond laser pulses
Optics letters, 1996
We demonstrate high-quality FM spectra with nanosecond laser pulses. Transform-limited pulses with FM sidebands are produced by pulsed amplification of a phase-modulated cw laser. The pulses can be shifted to the UV by nonlinear mixing. We report both initial experiments on I(2) and what is to our knowledge the first observation of a far-UV transition by FM spectroscopy, at 214.5 nm. Major advantages of this method include (1) spectral resolution of the order of 0.001 cm(-1), (2) better-defined optical phase, and (3) a much smaller and more easily detected modulation frequency, ~500 MHz. The absorption sensitivity is ~10(-4), and considerable further improvement is expected.
Applied Optics, 1992
Wavelength modulation spectroscopy (WMS) and one-tone and two-tone frequency modulation spectroscopy (FMS) are compared by measuring the minimum detectable absorbances achieved using a mid-IR lead-salt diode laser. The range of modulation and detection frequencies spans over 5 orders of magnitude. The best results, absorbances in the low-to-mid 10-7 range in a 1-Hz bandwidth, are obtained by using high-frequency WMS (10-MHz detection frequency) and are limited by detector thermal noise. This sensitivity can provide species detection limits well below 1 part per billion for molecules with moderate line strengths if multiple-pass cells are used. High-frequency WMS is also tested by measuring the absorbance due to tropospheric N 2 0 at 1243.795 cm-'. WMS at frequencies < 100 kHz is limited by laser excess (1/f) noise. Both of the FMS methods, which require modulating the laser at frequencies 2 150 MHz, give relatively poor results due to inefficient coupling of the modulation waveform to the laser current. The results obtained agree well with theory. We also discuss the sensitivity limitations due to interference fringes from unintentional 6talons and the effectiveness of 6talon reduction schemes.
Frequency modulation spectroscopy by means of quantum-cascade lasers
Applied Physics B, 2006
In this paper we investigate the performance of quantum cascade (QC) lasers for high frequency modulation spectroscopy, particularly using frequency modulation (FM) and two-tone (2T) techniques. The coupling of the rf signal to the QC laser through the cryostat is studied in detail as well as the noise contributions of both the detector and the laser source to the final spectra. The experimental traces are obtained by spectroscopy on low-pressure N 2 O and CH 4 gases at 8.0 µm and 7.3 µm wavelength, respectively, and reproduce the line profiles predicted by theory. As a preliminary result, an enhancement of a factor six is measured with respect to direct absorption line recording. PACS 42.62.Fi; 42.72.A1; 07.88.+y
Pulsed frequency-modulation spectroscopy as a means for fast absorption measurements
Optics Letters, 1981
Absorption measurements are accomplished by utilizing short pulses of frequency-modulated (FM) light. The absorption is measured by detecting the heterodyne beat signal that occurs when the FM spectrum is distorted by the absorption feature of interest. By using a single short laser pulse it is demonstrated that the beat signal can build up far above the noise level within 1 Asec. The entire absorption structure can be probed by a few laser pulses. Thus pulsed FM spectroscopy permits ultrafast absorption measurements to be made by using an overall light exposure several orders of magnitude smaller than is necessary for traditional absorption techniques.
Modulation cancellation method in laser spectroscopy
Applied Physics B, 2011
A novel spectroscopic technique based on modulation spectroscopy with two excitation sources and quartz enhanced photoacoustic spectroscopy is described. We demonstrated two potential applications of this detection technique. First, we investigated the measurement of small temperature differences in a gas mixture. In this case, a sensitivity of 30 mK in 17 sec was achieved for a C 2 H 2 /N 2 gas mixture with a 0.5% C 2 H 2 concentration. Second, we demonstrated the detection of broadband absorbing chemical species, for which we selected hydrazine as the target molecule and achieved a detection limit of ∼1 part per million in 1 sec. In both cases, the measurements were performed with near-IR laser diodes and overtone transitions.
Applied Optics, 1997
The capability of two-tone frequency-modulation spectroscopy ͑TTFMS͒ in deriving spectral line-shape information was investigated. Two oxygen A-band transitions at 760 nm were selected, and the Voigt profile and two different collisionally narrowed line profiles were employed in their analysis. By means of a least-squares fitting procedure, we obtained accurate information regarding transition strengths and pressure-induced broadening, shift, and narrowing coefficients. Both TTFMS and direct absorption line shapes were modeled with deviations as small as 0.3% over a wide pressure range by use of the collisionally narrowed line profiles. Line parameters measured with TTFMS showed excellent agreement with the parameters measured with direct absorption. The experimental technique used constantcurrent fast-wavelength scanning, which improved measurement accuracy.
Laser frequency stabilization by combining modulation transfer and frequency modulation spectroscopy
Applied optics, 2017
We present a hybrid laser frequency stabilization method combining modulation transfer spectroscopy (MTS) and frequency modulation spectroscopy (FMS) for the cesium D<sub>2</sub> transition. In a typical pump-probe setup, the error signal is a combination of the DC-coupled MTS error signal and the AC-coupled FMS error signal. This combines the long-term stability of the former with the high signal-to-noise ratio of the latter. In addition, we enhance the long-term frequency stability with laser intensity stabilization. By measuring the frequency difference between two independent hybrid spectroscopies, we investigate the short-and long-term stability. We find a long-term stability of 7.8 kHz characterized by a standard deviation of the beating frequency drift over the course of 10 h and a short-term stability of 1.9 kHz characterized by an Allan deviation of that at 2 s of integration time.
Recent advances in the field of laser atomic spectroscopy
TrAC Trends in Analytical Chemistry, 1993
An overview of recent advances in the field of analytical laser atomic spectroscopy will be discussed, in particular the laser's use as a light source in atomic absorption spectroscopy, as an excitation source in laser atomic fluorescence and laser enhanced ionization spectroscopy, as a method of solid sample introduction, and as a diagnostic tool. Selected current research in these fields will be highlighted together with their results.