ABSTRACT
We report, to the best of our knowledge, the first super-octave femtosecond polycrystalline Cr:ZnS laser at the central wavelength 2.4 µm. The laser is based on a non-polarizing astigmatic X-folded resonator with normal incidence mounting of the gain element. The chromatic dispersion of the resonator is controlled with a set of dispersive mirrors within one third of an optical octave over 2.05-2.6 µm range. The resonator's optics is highly reflective in the range 1.8-2.9 µm. The components of the oscillator's output spectrum at the wavelengths 1.6 µm and 3.2 µm are detected at -60 dB with respect to the main peak. Average power of few-cycle Kerr-lens mode-locked laser is 1.4 W at the pulse repetition frequency 79 MHz. That corresponds to 22% conversion of cw radiation of Er-doped fiber laser, which we used for optical pumping of the Cr:ZnS oscillator.
ABSTRACT
We report, to the best of our knowledge, the first fully referenced Cr:ZnS optical frequency comb. The comb features few cycle output pulses with 3.25 W average power at 80 MHz repetition rate, spectrum spanning 60 THz in the middle-IR range 1.79-2.86 µm, and a small footprint (0.1 m2), The spectral components used for the measurement of the comb's carrier envelope offset frequency were obtained directly inside the polycrystalline Cr:ZnS laser medium via intrinsic nonlinear interferometry. Using this scheme we stabilized the offset frequency of the comb with the residual phase noise of 75 mrads.
ABSTRACT
We report a technique for generation of broad and coherent femtosecond (fs) continua that span several octaves from visible to long-wave IR parts of the spectrum (0.4-18 µm). The approach is based on simultaneous amplification of few-cycle pulses at 2.5 µm central wavelength at 80 MHz repetition rate, and augmentation of their spectrum via three-wave mixing in a tandem arrangement of polycrystalline Cr:ZnS and single crystal GaSe. The obtained average power levels include several mW in the 0.4-0.8 µm visible, 0.23 W in the 0.8-2 µm near-IR, up to 4 W in the 2-3 µm IR, and about 17 mW in the 3-18 µm long-wave IR bands, respectively. High brightness and mutual coherence of all parts of the continuum was confirmed by direct detections of the carrier envelope offset frequency of the master oscillator.
ABSTRACT
We report a significant breakthrough in the development of fiber-pumped high-power CW laser systems based on Cr2+:ZnS and Cr2+:ZnSe gain media. We demonstrate output power levels of up to 140 W near 2500 nm, and 32 W at 2940 nm with corresponding optical efficiencies of 62% and 29%. Our novel approach is based on rapid simultaneous scanning of the collinear laser mode and pump beam across the Cr:ZnS/Se gain element which allows us to virtually eliminate thermal lensing effects and obtain unprecedented levels of output power with very high optical-to-optical efficiency.
ABSTRACT
Dual-comb spectroscopy (DCS) has shown unparalleled advantages but at the cost of highly mutual coherence between comb lasers. Here, we investigate spectral degradation induced by laser frequency instabilities and improvement benefited from active laser stabilization. Mathematical models of DCS in the cases of direct radio-frequency (RF) locking and optical phase stabilization were separately established first. Numerical simulations are utilized to study the impact of laser intrinsic stability and the improvement by different locking strategies on spectral performance in the following. Finally, both simulations are proven by corresponding experiments. It shows that an optically phase-stabilized system owns a better immunity of laser frequency fluctuations than a direct RF-stabilized one. Furthermore, the performance improvement by the feedback servos is also more effective in the optically phase-stabilized system. In addition, the simulations could instruct optimal design and system improvement.
