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A 100-fs Cr:ZnSe laser, based on a ceramic active medium, generates 100 mW at 215 MHz repetition rate around 2450 nm. Co-propagating second-harmonic pulse at 1225 nm is simultaneously generated due to random quasi-phase-matching process. 2010 Optical Society of America OCIS codes: 140.3070 Infrared and far-infrared lasers, 140.7090 Ultrafast lasersIn the last few years we evidence a growing interest to Cr 2+ -doped lasers of the II-VI family [1] operating in the "molecular fingerprint" range between 2 and 3.5 μm. The Cr:ZnSe laser has the broadest bandwidth ∆λ/λ among all known room-temperature solid-state active media [1]. The first femtosecond operation (80 fs) using SESAM has been reported in 2006 [2] and KLM mode-locking has been reported in June 2009 [3]. Ceramic Cr:ZnSe laser has been realized in the active mode-locked regime [4]. A special peculiarity of the ZnSe type crystals as active media is the presence of the second-order nonlinearity [5], which makes simultaneous generation of femtosecond pulses at the fundamental and second harmonic (SH) wavelengths possible. The intracavity SH generation from a Cr:ZnSSe laser in continuous-wave regime was observed in [6].In this work, we present a ceramic femtosecond Cr2:ZnSe laser, generating ultrashort pulses at the fundamental (2.45 μm) and the second harmonic wavelength (1.22 μm) simultaneously. This is the first laser of this type, opening up interesting application opportunities. Figure 1: Experimental set-up, mode-locked output spectrum at 2450 nm and a corresponding round-trip group-delay dispersion of the cavity. The "noise" features at the spectrum are due to the intracavity water vapour absorption lines [7,8].The experimental setup is shown in Fig. 1. For dispersion compensation, a single 3-mm thick sapphire plate was used, that was sufficient to compensate the 2-mm thick ceramic sample (Cr concentration 5·10 18 cm -3 ) from Photonics Innovations, Inc. The samples were edge-mounted without active cooling and absorbed ~65% of pump radiation. Reliable self-starting of mode-locking operation (i.e. restarting after interrupting the pump or intracavity beams) was observed at 1.8-2.1 W of pump power, although the laser could be modelocked in the 0.9 -2.2 W pump power range, delivering 45 to 120 mW of average output power at 215 MHz repetition rate. All measurements were performed at ambient atmosphere with relative humidity 40-50%. The autocorrelation (AC) was measured by a collinear autocorrelator using two-photon absorption in an InGaAs photodiode.

Abstract:We analyze the third harmonic generation by the supercontinuum at 1.5 µm in nonlinear-glass microstructured fibers. The numerical model includes the real field dynamics and allows analyzing the spectral as well as the temporal structure of the generated field. The calculated third harmonic and supercontinuum spectra are compared with the experiment in the SF6 glass PCF pumped by a femtosecond Cr 4+ :YAG oscillator. The spectral structure of the third harmonic is composed of the 10-20 high-order modes excited at the phase matching points around 500-550 nm. The individual third harmonic modes have spectral widths of 2-4 nm. In the time domain, the third harmonic signal is a ∼10-ps pulse with psscale slow modulation, containing subpicosecond ripples at its trailing edge. References and links1. J. M. Dudley, G. Genty, S. Coen, "Supercontinuum generation in photonic crystal fiber," Rev. Mod. Phys. 78, 1135-1184 (2006). 2. V. L. Kalashnikov, E. Sorokin, I. T. Sorokina, "Raman effects in the infrared supercontinuum generation in softglass PCFs," Appl. Phys. B. 87, 37-44 (2007) 3. R. H. Stolen, "Phase-matched-stimulated four-wave mixing in silica-fiber waveguides," IEEE J. Quantum Electron. QE-11, 100-103 (1975)

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We report the proof-of-concept of an operational laser active medium with a depressed cladding waveguide manufactured in the volume of a Cr2+:ZnS single-crystalline sample and antireflection microstructures fabricated on its facets exclusively by femtosecond laser processing techniques. This allowed us to achieve transmittance in a broad range from 2 to 8 µm, approaching a maximum of over 90% near 2.5 µm, and lasing at 2275 nm at the average output power of 20 mW for the absorbed pump power of 500 mW with the slope efficiency of 5.5 %. This demonstration opens up a route towards the industrial fabrication of compact integrable laser sources and sensors based on II-VI materials.