Characterization of an external cavity diode laser based ring cavity NICE-OHMS system

Abstract

The performance of an external cavity diode laser based noise immune cavity enhanced optical heterodyne molecular spectrometer is presented. To reduce the noise on the signal a ring cavity and a circuit to remove residual amplitude modulation on the pre-cavity laser radiation was implemented. We demonstrate a sensitivity of 4 x 10(-11) cm(-1) Hz(-1/2) using a cavity with a finesse of 2600 on a Doppler-broadened transition of CH(4) at 6610.063 cm(-1).

Shot-noise-limited Doppler-broadened noise-immune cavity-enhanced optical heterodyne molecular spectrometry

“…An exception is the most recent demonstration in which a differential mode of detection was utilized, which could provide a detection sensitivity that was only a factor of 4 above the shot noise limit. The cause for the limited performance of these systems is usually attributed to noise from background signals [8].…”

External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation

“…cm −1 Hz -1/2 with higher cavity finesses and wavelength modulation [4,6]. The system can be enhanced by the use of a higher cavity finesse and more advanced servo circuitry.…”

“…Continuing this research, the technique has been implemented with various other lasers like fiber [3] or external cavity diode lasers (ECDL) [4][5][6]. The latter have a broader linewidth than Nd:YAG and fiber lasers, but possess the advantage of compactness and tunability over a wide wavelength range, making them ideal for molecular absorption applications in the near-IR.…”

“…The latter have a broader linewidth than Nd:YAG and fiber lasers, but possess the advantage of compactness and tunability over a wide wavelength range, making them ideal for molecular absorption applications in the near-IR. For example, Bell et al detected CH 4 using an ECDL, achieving a NEAS of 4 x 10 −11 cm −1 Hz -1/2 with a finesse of 2600 [6]. The future potential for NICE-OHMS applications, however, resides in the realization of laser-based spectrometers operating in the molecular fingerprint region in the mid-IR.…”

Fiber-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectrometry incorporating an optical circulator

“…In its original realization based on a narrow linewidth fixed-frequency Nd:YAG laser and a cavity with a finesse of 10 5 , an astonishing detection sensitivity of 10 −14 cm −1 for 1 s integration time was demonstrated in sD detection of C 2 HD for frequency metrology purposes [1]. Since then, several attempts have been made to benefit from this extreme detection sensitivity and widen the applicability of the technique by the realization of instruments based on other types of lasers [2][3][4][5][6][7][8]. However, so far the sensitivities obtained have not matched that of the first realization for at least two reasons.…”