The combination of frequency combs and quantum cascade lasers is opening new opportunities in the field of precision spectroscopy in the mid-infrared. Frequency combs allow quantum cascade lasers to be referenced to a highly repeatable, precise and absolute frequency axis. Repeatability is a key feature to obtain high quality measurements of absorption profiles and thus accurate determination of spectroscopic parameters, while absolute frequency calibration makes it possible the comparison of spectroscopic data acquired in different laboratories and at different times, as well as comparison with theoretical predictions or existing databases. This work reviews some of the main results achieved at 4.3 μm by investigation of a manifold of rovibrational lines of CO2. Spectroscopic parameters such as line-centre frequencies, line intensity factors, pressure shift and pressure broadening coefficients are retrieved with an unprecedented quality from the metrological point of view.
Recently, great effort has been devoted to waveguide lasers, because of their inherent simplicity with respect to
fiber lasers. Actually, due to their compactness, such lasers are expected to achieve a higher temporal coherence,
making them attracting for fiber optical reflectometry, distribute sensing, and range finding applications. Furthermore,
the availablity of fast saturable absorbers based on carbon nanotubes allows for a cheap and reliable
implementation of the passive mode-locking technique with the potential for generating high repetition rate pulse
trains. Such lasers will provide low-noise and inexpensive pulsed sources for applications in optical communications,
optically sampled analog-to-digital converters, and spectral line-by-line pulse shaping. We report here on
advanced waveguide lasers, operating both in continuous wave and pulsed regimes, based on active waveguides
fabricated by femtosecond laser writing in a phosphate glass substrate. A single longitudinal mode waveguide
laser providing more than 50 mW with 21% slope efficiency was demonstrated. Furthermore, by combining a high
gain waveguide and an innovated fiber-pigtailed saturable absorber based on carbon nanotubes, a mode-locked
ring laser providing transform limited 1.6-ps pulses was also demonstrated.
A theoretical and experimental analysis of group velocity reduction in periodic super-structured Bragg gratings
is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the 1.5 μm wavelength of optical communications is reported using either a 20-cm-long Moire and a periodically-spaced πphase shift fiber gratings. Time delays up to approximately 690 ps for 250-ps-duration optical pulses have been achieved leading to the realization of an optical buffer.
A review on the results achieved by our group in the development of novel solid-state lasers for Lidar applications at 2 μm is presented. These lasers, based on fluoride crystals (YLF4, BaY2F8, and KYF4) doped with Tm and Ho ions, are characterized by high-efficiency and wide wavelength tunability around 2 μm. Single crystals of LiYF4, BaY2F8, and KYF4 codoped with the same Tm3+ and Ho3+ concentrations were successfully grown by the Czochralski method. The full spectroscopic characterization of the different laser crystals and the comparison between the laser performance are presented. Continuous wave operation was efficiently demonstrated by means of a CW diode-pumping. These oscillators find interesting applications in the field of remote sensing (Lidar and Dial systems) as well as in high-resolution molecular spectroscopy, frequency metrology, and biomedical applications.
Preliminary results on absolute frequency stabilization of Distributed Bragg Reflector (DBR) diode-lasers with emission wavelength at 852 nm will be reported. Saturated absorption D2 lines of cesium atom have been adopted as a frequency reference and the nonlinear spectroscopy method of Modulation Transfer has been used to lock the laser frequency against the resonance. From the preliminary results on the beat signal between two independent laser systems a relative frequency stability of 10-11 has been reached at an integration time of 0.1 s. The analysis on the obtained signal to noise ratio shows a frequency noise floor in the order of approximately 10-12 which should be achieved in an integration time of 1 s.
A novel Er-Yb:glass quasi-monolithic diode-pumped laser has been developed to realize a high-accuracy frequency standard at 1.54 micrometer based on saturated absorption of isotopic acetylene. This compact oscillator shows low amplitude- and frequency-noise, wide wavelength tunability (approximately 20 nm), and continuous output power in excess of 20 mW with excellent linear polarization (approximately 30 dB extinction ratio). Employing this laser source sub-Doppler spectroscopy of the acetylene around 1.54 micrometer has been performed. To obtain the necessary saturation intensity (approximately 3.5 W/mm2), the absorbing sample is placed inside a Fabry- Perot cavity with a Finesse of approximately 150. The dispersion signal of the sub-Doppler resonance, useful to stabilize the laser frequency, has been obtained by dithering the Fabry-Perot piezo and employing a lock-in detection scheme.