Absolute spectroscopy of N_2O near 45 μm with a comb-calibrated, frequency-swept quantum cascade laser spectrometer

Abstract

We present absolute line center frequencies for 24 fundamental ν3 ro-vibrational P-branch transitions near 4.5 μm in N2O with an absolute expanded (multiplied by 2) frequency uncertainty of 800 kHz. The spectra are acquired with a swept laser spectrometer consisting of an external-cavity quantum cascade laser whose instantaneous frequency is continuously tracked against a near-infrared frequency comb. The measured absorbance profiles have a well-calibrated frequency axis, and are fitted to determine absolute line center values. We discuss the main sources of uncertainty.

Real-Time Dynamic Atomic Spectroscopy Using Electro-Optic Frequency Combs

“…Alternatively, timeresolved broad spectra can be obtained with the use of a swept-laser source. Tunable lasers can reach speeds on the order of 1-100 THz=s [23][24][25], with speeds exceeding 1000 THz=s just within reach [26]. Yet, high-speed tunable-laser spectroscopy faces two intrinsic challenges.…”

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy

“…At the moment, however, the fully stabilized mid-infrared OFCs are rather complex and are not commercially available. A more common solution is to reference the MIR laser to an NIR OFC via nonlinear optical frequency conversion [11][12][13][14][15][16][17][18][19]. This is typically done by using continuous-wave (cw) DFG [12,14] or a cw OPO [11,[15][16][17], following the scheme of Fig.…”

“…1(a). In addition, referencing of a narrow-linewidth laser to an NIR OFC by sum frequency generation (SFG) has been used at wavelengths longer than 4 µm [13,18,19].…”

Frequency locking of an extended-cavity quantum cascade laser to a frequency comb for precision mid infrared spectroscopy

“…This is one of the reasons why neither their frequency nor their phase have been so far locked to a frequency comb. Their use in combination with frequency combs has been performed in an open loop regime only [2], which has the merit of preserving the inherently fast modulation speed of these lasers, yet not to afford high spectral resolution and accuracy.Here we report for the first time frequency locking of an EC-QCL to a frequency comb. The lock relies on an external frequency correction given by an acousto-optical frequency shifter (AOFS) in a feedback configuration, according to the experimental setup depicted in Fig.…”

“…This is one of the reasons why neither their frequency nor their phase have been so far locked to a frequency comb. Their use in combination with frequency combs has been performed in an open loop regime only [2], which has the merit of preserving the inherently fast modulation speed of these lasers, yet not to afford high spectral resolution and accuracy.…”