Sub-Doppler resolution near-infrared spectroscopy at 128  μm with the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy method

Abstract

We report on the Doppler-free saturation spectroscopy of the nitrous oxide (N 2 O) overtone transition at 1.28 µm. This measurement is performed by the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique based on the quantum-dot (QD) laser. A high intra-cavity power, up to 10 W, reaches the saturation limit of the overtone line using an optical cavity with a high finesse of 113,500. At a pressure of several mTorr, the saturation dip is observed with a full width at halfmaximum of about 2 MHz and a signal-to-noise ratio of 71. To the best of our knowledge, this is the first saturation spectroscopy of molecular overtone transitions in 1.3 µm region. The QD laser is then locked to this dispersion signal with a stability of 15 kHz at 1 sec integration time. We demonstrate the potential of the N 2 O as markers because of its particularly rich spectrum at the vicinity of 1.28-1.30 µm where lies several important forbidden transitions of atomic parity violation measurements and the 1.3 µm O-band of optical communication. http://dx.doi.org/10.1364/ao.XX.XXXXXX High-resolution spectroscopy plays an essential role in widespread applications in sciences including astronomy, physics, chemistry and biology. The Doppler-free spectrum provide a significant improvement in spectroscopic resolution relative to Doppler-broadened line shapes. Few results were reported in near-infrared (NIR) region by means of saturation spectroscopy, because a relatively high power is required. However, NIR is an important spectral range not only offer laboratory comparisons for the research on astrophysical phenomena [1,2], but also to provide a powerful analytical tool to the studies of molecular rotation-vibration structure [3]. While most atmosphere molecules such as CO 2 , CO, CH 4 , C 2 H 2 , H 2 O, HF, and N 2 O all present strong fundamental vibrational transitions beyond 2 µm, the overtone transitions falling in the 1-2 µm range are one to two orders of magnitude less intense [3][4][5]. They are often with integrated line strengths (<10 −23 cm −1 /molecule cm −2 ). Although it can be observed using highly sensitive techniques, such as cavity-ring down spectroscopy, most of the results are Doppler-limited. So far, the Doppler-free saturation spectrum in the 1.5 µm region has been successfully observed using cavitybased spectroscopy [6,7], but only the Doppler-limited spectrum has been reported in the 1.1 µm-1.3 µm band [8][9][10], which is with even smaller dipole moments .On the other hand, considerable progress in QD lasers engineering development results in the broad availability of efficient InGaAs QD diode applied for NIR laser sources. Particularly in the 1.1-1.3 µm band, QD diode based lasers have demonstrated their superior performances in several respects in comparison with traditional quantum-well based diode lasers [11]. Many important applications in this spectral range require stabilized laser sources, such as the coarse wavelength division multiplexing (CWDM) technology at 1.3 µm [12], ...

Frequency metrology of molecules in the near-infrared by NICE-OHMS

“…WM-modulation amplitude and frequency -Wavelength modulation is made by dithering the cavity length through the piezo actuator. This modulation helps to eliminate the slow baseline drift in the dispersion NICE-OHMS signal which often comes from residual amplitude modulation (RAM) in the frequency modulation or other etalon effects [40]. However, special caution must be paid since the modulation could also impose distortions on the line profile.…”

Cavity-enhanced saturation spectroscopy of molecules with sub-kHz accuracy

“…The technique was first demonstrated as a frequency reference at 1064 nm by Ye et al [17], giving an astonishing sensitivity of 10 −14 cm −1 [18]. This extremely sensitive technique has been applied to lock lasers with molecular transitions [17,19,20] without giving the absolute frequencies.…”

Laser frequency stabilization based on a universal sub-Doppler NICE-OHMS instrumentation for the potential application in atmospheric lidar

“…A variety of tunable lasers, including an external cavity diode laser (ECDL) (Bell et al, 2009;Chen and Liu, 2015;Dinesan et al, 2014;Ishibashi and Sasada, 2000;Saraf et al, 2016;van Leeuwen and Wilson, 2004), quantum cascade laser (QCL) (Taubman et al, 2004), optical parametric oscillator (OPO) (Hausmaninger et al, 2015;Talicska et al, 2016;Taubman et al, 2004), quantum-dot laser (Chen and Liu, 2017), distributed feedback laser (DFB) (Foltynow-icz et al, 2010) and whispering-gallery-mode (WGM) laser (Zhao et al, 2017), have been applied to the NICE-OHMS system over the years. The most persistent development of NICE-OHMS has been performed based on erbium-doped fiber lasers (EDFLs), which lase in the near-IR (NIR) region (Ehlers et al, 2012;Schmidt et al, 2007).…”