Colquiriite Crystals Research Articles

Temperature dependence of the emission cross-section and fluorescence lifetime in Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF between 78 K and 618 K

Cr:Colquiriites (Cr:LiCAF, Cr:LiSAF, and Cr:LiSGaF) are well-known for their broad emission bands in the near-infrared region. Unfortunately, due to their relatively weak thermomechanical strength, average powers from Cr:Colquiriite lasers have been so far limited to sub-5 W level in continuous-wave operation at room temperature. In this study, the promise of cryogenic operation, which shows significant power scalability in Yb-based systems, is investigated in detail for Cr-doped Colquiriite crystals in terms of the temperature dependence of the fluorescence lifetime and emission cross-section (σ e ) in the 78-618 K range. The lifetime measurements showed that the fluorescence, as well as the radiative lifetimes of Cr:Colquiriites are temperature dependent. The emission cross-section measurements revealed that while cooling the crystals from 300 K to 78 K, the peak σ e in E||c polarization increases moderately for all crystals: from around 1.3 × 10−20 cm2 to 1.6 × 10−20 cm2 in Cr:LiCAF, from around 4.5 × 10−20 cm2 to 6.3 × 10−20 cm2 in Cr:LiSAF and from around 3.1 × 10−20 cm2 to 3.95 × 10−20 cm2 in Cr:LiSGaF. We provide analytical formulas describing the measured temperature dependence of all relevant quantities such as fluorescence/radiative lifetime, peak emission wavelength, peak emission cross-section, and emission full-width at half-maximum. Overall, the reported results constitute a solid basis for the modeling of Cr:Colquiriite-based laser and amplifier systems, especially for the assessment of their potential at cryogenic temperatures.

Discrimination between thermal quenching of the fluorescence and Auger upconversion processes using thermal lens technique

In this work we used the Thermal Lens (TL) technique to discriminate two important processes responsible to reduce the upper-state population and fluorescence quantum efficiency (η) in Cr3+ doped colquiriite crystals: the thermal quenching of the fluorescence (TQF) and the Auger upconversion (ETU). We observed a nonlinear increase of the TL signal with laser power due to the decrease of η by ETU and/or TQF. The analysis of these curves allowed the determination of the thermal load, the increase of the crystal temperature as a function of the pump excitation and the discrimination between ETU and TQF processes.

Directly diode-pumped Colquiriite regenerative amplifiers

The Colquiriite crystals are attractive materials for directly diode-pumped femtosecond oscillators and amplifiers. Cr:LiSAF, Cr:LiSGAF and Cr:LiCAF are for the first time directly compared for their use in regenerative amplifiers both experimentally and theoretically. A maximum pulse energy of 10μJ was obtained at an absorbed pump power of 1.1W. A review of the work is given including a Cr:LiSAF seed oscillator, outlining specific needs for seeding.

Thermal quenching of the fluorescence quantum efficiency in colquiriite crystals measured by thermal lens spectrometry

The dual-beam mode-mismatched thermal lens technique was used to study the temperature dependence of the absolute fluorescence quantum efficiency (η) of a thermal-quenching fluorescence (TQF) process in Cr3+-doped colquiriite crystals (LiSAF and LiSGaF), from 300 to 450 K. The research was developed at a low excitation-power level in order to eliminate the energy-transfer upconversion effect. The results showed that TQF is the main loss mechanism involved. The thermal diffusivity, the thermal conductivity, and the specific heat of the samples were also measured in the same temperature range.

Generation of sub-10-fs pulses from a Kerr-lens mode-locked Cr^3+:LiCAF laser oscillator by use of third-order dispersion-compensating double-chirped mirrors

Pulses as short as 9 fs at 220-mW average power and a 97-MHz repetition rate are generated from a cw Ti:sapphire-pumped Kerr-lens mode-locked Cr(3+)LiCAF laser oscillator employing broadband double-chirped mirrors for second- and third-order dispersion compensation. Fine adjustment of dispersion is accomplished with a fused-silica prism pair. The result demonstrates that Raman-induced self-frequency shifting of the pulse does not limit sub-10-fs pulse generation from colquiriite crystals.

Thermally induced optical bistability in Cr-doped Colquiriite crystals

We have shown that a very strong nonlinearity in the temperature dependence of the luminescence quantum yield in Cr-doped laser crystals of the Colquiriite family can lead to a temperature induced intrinsic optical bistability in these materials. The bistability and the hysteresis loop in the dependence of Cr luminescence intensity and transmission of the crystal on cw pumping power has been theoretically predicted and experimentally observed. The experimental results are in a good qualitative and quantitative agreement with the theoretical prediction.

Material and laser characterizations of intermediate compositions of Ce : LiSrxCa1−xAlF6

The development of solid state tunable lasers in the ultraviolet region would have a wide range of applications, including atmospheric remote sensing, atmospheric spectroscopy and pollution monitoring. The first work with Ce:LiCAF was published in 1993, with subsequent reports on favorable results with Ce:LiSAF. While the optical quality of Ce:LiSAF is superior, it suffers from solarization. In contrast, Ce:LiCAF shows minimal solarization and higher efficiencies, even with the typically high-scatter materials available. This presentation will summarize the crystal growth and material characterization of a series of colquiriite crystals with various Sr:Ca ratios. Based on these results, in addition to laser measurements, an optimum composition of Ce:LiSrxCa1−xAlF6 will be determined.

Progress in the crystal growth of Ce : colquiriites

The search for an efficient solid-state laser with tunable emission in the ultraviolet wavelength region has resulted in the growth and development of cerium-doped colquiriite crystals, such as LiCaAlF 6 (LiCAF) and LiSrAlF 6 (LiSAF). Unfortunately, the doping of LiSAF and LiCAF with Ce 3+ introduces different variables into the growth of high optical quality crystals, due to the charge imbalance induced when this trivalent ion substitutes for the divalent site. Charge compensation with Na + tends to produce a more uniformly doped crystal with improved laser properties. Although preliminary research indicated that Ce : LiSAF may be the preferred material of the colquiriite hosts, Ce : LiCAF has also proved to be quite promising.