AFLSC2019

A Widely Tunable 10-μm QCL Locked to a Metrological Mid-IR Reference for Precision Molecular Spectroscopy

29 Jan 2019, 16:35

5m

Ernest Aryeetery Hall (Bank of Ghana Conf Facility, Uni Ghana.)

Poster Presentations AfLS2 track AfLS2 Poster Session

Speaker

Dr Papa Lat Tabara SOW (Université Alioune DIOP de Bambey)

Description

The quantum cascade lasers (QCL) are popular sources for spectroscopy in the field of mid-infrared because of the wide range of wavelengths they can cover (3 μm <λ< 24 μm). Several examples of spectroscopic measurements with spectrometers based on QCL, have been demonstrated [2]. We are currently developing a laser spectrometer based on a QCL which emits around 10 μm. The selection of this wavelength for the QCL source is to compare it to our existing ultra-stable CO2 lasers. We characterized a free-running continuous wave near-room-temperature distributed feedback 10.3 μm QCL. This gave a remarkable result on the frequency noise which is an order of magnitude smaller compared to what was published on the characterization of these types of lasers sources. A full width at half maximum (FWHM) equal to 60 kHz of the beat signal between the free-running QCL and a 1-kHz narrow CO2 laser was observed after 1 ms of integration time. Narrowing of the QCL line width has been made by taking a phase-locked QCL on the CO2 laser which is itself stabilized on a saturated absorption transition of the OsO4 molecule. The beat spectrum between phase-locked QCL and CO2 laser recorded with a radio-frequency (RF) spectrum analyzer allowed us to estimate that more of 99% of the beat signal RF power is concentrated in the carried. This allows to conclude that the QCL was copied almost exactly the spectral characteristics of our ultra-stable CO2 laser (10-Hz line width, accuracy of a few tens of hertz). These results in a record QCL line width of the order of 10 Hz, 3 to 4 orders of magnitude lower than a free-running QCL, and a relative stability at 1 s of about 1 Hz. The phase-locked QCL was then used to measure the spectra of ammonia (NH3) and methyltrioxorhenium (MTO) to demonstrate its potential for two main projects of our group: the determination of the Boltzmann constant, kB, by Doppler spectroscopy of ammonia [3] and the first observation of parity violation by Ramsey interferometry of a beam of chiral molecules [4]. References [1] Kosterev et al.. Applied Physics B, 90(2), 165-176 (2008) [2] Wysocki et al. Applied Physics B, 92(3), 305-311 (2008) [3] C. Lemarchand et al. Metrologia 50 623 (2013) [4] S. K. Tokunaga et al. Molecular Physics 111, Issue 14-15, 2363–2373 (2013)