Diode-pumped regenerative Yb:SrF2 amplifier

International audienceWe report what we believe to be the first Yb:SrF2 regenerative femtosecond amplifier. The regenerative amplifier produces 325-fs pulses at 100-Hz repetition rate with an energy before compression of 1.4 mJ. The interest of Yb:SrF2 in such regenerative amplifiers and its complementarity to its well-known isotype Yb:CaF2 is also discussed

Diode-pumped Yb:CaF 2 multipass amplifier producing 50 mJ with dynamic analysis for high repetition rate operation

International audienceThe dynamic thermal issues of the Yb:CaF 2 crystals within a multi-tens-mJ-energy multipass amplifier operating in the 20–100 Hz repetition rate range and pumped in quasi-cw regime have been studied at different timescales. Thermal response times of the system have been precisely investigated and analyzed, for the first time to our best knowledge in such amplifiers. This study includes a dual timescale analysis: in the long-timescale (second) with direct thermography mapping and in the millisecond range with thermal lensing in a pump-probe configuration. Very atypical positive lens behavior with fluorites will also be presented and discussed. This complete analysis is used to demonstrate the capability of Yb:CaF 2 multipass amplifier systems for operating the amplifier at 20 Hz with 57 mJ and 100 Hz with 32-mJ stable regime. Indeed, high repetition rate multipass amplifier has been realized for the first time with Yb:CaF 2 and for this energy. The results have been analyzed precisely to take into account the thermal issues and excellent beam quality, with a M 2 of 1.1. The pointing stability of 20 lrad has been measured documenting the reliability of the high repetition rate mJ amplifier

Mode-locked operation of a diode-pumped femtosecond Yb : SrF2 laser

International audienceFemtosecond mode-locked operation is demonstrated for the first time, to our knowledge, with a Yb:SrF2 crystal. The shortest pulse duration is 143 fs for an average power of 450 mW. The highest average power is 620 mW for a pulse duration of 173 fs. Since Yb:SrF2 corresponds to the longest-lifetime Yb-doped crystal with which the mode-locking operation has been achieved, a detailed analysis is carried out to characterize the quality of the solitonlike regime

On Yb:CaF2 and Yb:SrF2 : Review of spectroscopic and thermal properties and their impact on femtosecond and high power laser performance

International audienceWe present an overview of laser results we obtained with Yb-doped calcium fluoride and its isotype strontium fluoride. In order to study the laser performance in femtosecond and high power regimes, spectral and thermal properties are first discussed including the potential of these crystals at room and cryogenic temperatures. Experimental demonstrations of high-power and ultrashort pulse oscillators and amplifiers are presented and analyzed

High-power diode-pumped cryogenically cooled Yb:CaF2 laser with extremely low quantum defect

International audienceHigh-power diode-pumped laser operation at 992-993nm under a pumping wavelength of 981 of 986nm is demonstrated with Yb:CaF2 operating at cryogenic temperature (77K), leading to extremely low quantum defects of 1.2% and 0.7%, respectively. An average output power of 33Whas been produced with an optical efficiency of 35%. This represents, to the best of our knowledge, the best laser performance ever obtained at such low quantum defects on intense laser lines

Thermal behaviour of ytterbium-doped fluorite crystals under high power pumping

International audienceWe report an in situ thermal study of Yb-doped fluorite crystals Yb:CaF2 and Yb:SrF2 under high power pumping, with or without laser operation. The experiment combines simultaneously thermography and measurement of the thermal aberrations. This setup allows us to measure temperature gradients, thermal lens, and absorption coefficients. From these measurements, we evaluate the thermal conductivity, fractional thermal load, and thermo-optic coefficient. Great differences are observed between the lasing and non lasing regimes. Our measured thermal lenses are greater than what are expected from the thermo-optic parameters found in previous work. Based on this thermal study, we design a laser cavity operating with large output power and TEM00, leading to better performances for Yb:CaF2 than Yb:SrF2

Co-doped Dy3+ and Pr3+ Ga5Ge20Sb10S65 fibers for mid-infrared broad emission

Rare earth ion doped materials are means to obtain cost-effective infrared light sources, with enough brilliance for applications such as gas sensing. Within a sulfide matrix, the simultaneous luminescence of both Pr3+ and Dy3+ in the Ga5Ge20Sb10S65 glass is reported. The use of these two rare earths is giving rise to a broad continuous luminescence in the 2.2–5.5 µm wavelength range, which could be used as a mid-infrared light source for gas-sensing applications. The demonstration of CO2 and CH4 detection using a fiber drawn from these materials is reported

Influence of fabrication steps on optical and electrical properties of InN thin films

This paper reports on a case study of the impact of fabrication steps on InN material properties. We discuss the influence of annealing time and sequence of device processing steps. Photoluminescence (PL), surface morphology and electrical transport (electrical resistivity and low frequency noise) properties have been studied as responses to the adopted fabrication steps. Surface morphology has a strong correlation with annealing times, while sequences of fabrication steps do not appear to be influential. In contrast, the optical and electrical properties demonstrate correlation with both etching and thermal annealing. For all the studied samples PL peaks were in the vicinity of 0.7 eV, but the intensity and full width at half maximum (FWHM) demonstrate a dependence on the technological steps followed. Sheet resistance and electrical resistivity seem to be lower in the case of high defect introduction due to both etching and thermal treatments. The same effect is revealed through 1/f noise level measurements. A reduction of electrical resistivity is connected to an increase in 1/f noise level

Diode-pumped 99 fs Yb : CaF2 oscillator

International audienceWe demonstrate the generation of 99 fs pulses by a mode-locked laser oscillator built around a Yb:CaF2 crystal. An average power of 380 mW for a 13 nm bandwidth spectrum centered at 1053 nm is obtained. The short-pulse operation is achieved thanks to a saturable absorber mirror and is stabilized by the Kerr lens effect. We investigated the limits of the stabilization process and observed a regime slowly oscillating between mode locking and Q switching

Optically pump-induced athermal and nonresonant refractive index changes in the reference Cr-doped laser materials: Cr:GSGG and ruby

The refractive index of most ion-doped materials increases with the excited state population. This effect was studied in many laser materials, particularly those doped with 'Cr POT. 3+' and rare earth ions, using several techniques, such as interferometry, wave mixing, and Z-scans. This refractive index variation is athermal (has an electronic origin) and is associated with the difference in the polarizabilites of the 'Cr POT. 3+' ion in its excited and ground states, 'delta''alfa IND. p'. The 'Cr POT. 3+' optical transitions in the visible domain are electric-dipole forbidden, and they have low oscillator strengths. Therefore, the major contribution to 'delta''alfa IND. p' has been assigned to allowed transitions to charge transfer bands (CTBs) in the UV with strengths 'DA ORDEM DE' 3 orders of magnitude higher. Although this CTB model qualitatively explains the main observations, it was never quantitatively tested. In order to further investigate the physical origin of 'delta''alfa IND. p' in 'Cr POT. 3+'-doped crystals, excited state absorption (ESA) and Z-scan measurements were thus performed in Cr:'Al IND. 2''O IND. 3' (ruby) and Cr:GSGG. Cr:GSGG was selected because of the proximity of its 'ANTPOT. 2 E' and '4 ANTPOT. T IND. 2' emitting levels, and thus the possibility to explore the role of the spin selection rule in the ESA spectra and the resulting variations in polarizability by comparing low and room temperature data, which were never reported before.On the other hand, Cr:'Al IND. 2''O IND. 3'(ruby) was selected because it is the only crystal for which it is possible to obtain CTB absorption data from both ground and excited states, and thus for which it is possible to check the CTB model more accurately. Thanks to these more accurate and more complete data, we came to the first conclusion that the spin selection rule does not play any significant role in the variation of the polarizability with the 'ANTPOT. 2 E'-'4 ANTPOT. T IND. 2' energy mismatch. We also discovered that using the CTB model in the case of ruby would lead to a negative 'delta''alfa IND. p' value, which is contrary to all refractive index variation (including Z-scan) measurements