Cr:LiSr(0.8)Ca(0.2)AlF(6) tunable laser

Power scaling potential of continuous-wave Cr:LiSAF and Cr:LiCAF lasers in thin-disk geometry

Continuous-wave (cw) output power from Cr:Colquiriite lasers is currently limited to the 3 W level due to weak thermal and mechanical properties of the Colquiriite host that hinders power scaling efforts. Thin-disk (TD) geometry, which has enabled record power levels in Yb:YAG gain media, has not yet been thoroughly studied for Cr:Colquiriites. In this work, we have numerically investigated the cw lasing potential of TD Cr:LiSAF and Cr:LiCAF lasers in detail. Our analysis has shown that, due to their low thermal conductivity and high susceptibility to temperature quenching of fluorescence lifetime, TD lasers based on Cr:LiSAF will require usage of ultrathin (100 μm thick) crystals with large diameters (15-25 mm), which will be difficult to prepare/handle due to its glass-like thermomechanical strength. Assuming such TD crystals could be produced, we estimate that cw powers above 15 W might be feasible from Cr:LiSAF thin-disk lasers (TDLs) pumped by a 100 W red diode. As an alternative, usage of Cr:LiCAF, which is the strongest member of Cr:Colquiriites in terms of thermomechanical properties, enables tighter focusing of a pump beam on the TD, which in turn facilitates adoption of smaller-diameter samples (10 mm). We have estimated that, when the thermally stronger c axis is used for heat extraction and the a axis is used for lasing, cw powers exceeding 30 W could be achieved from Cr:LiCAF TDLs at an incident pump power of 100 W. On the other hand, our model shows that the small signal gain that could be achieved via cw pumping of Cr:Colquiriite TD elements is below 0.5%. Hence, the aforementioned performance requires usage of high-quality factor cavities with minimal intracavity losses.

Low-cost, broadly tunable (375-433 nm & 746-887 nm) Cr:LiCAF laser pumped by one single-spatial-mode diode

We describe a low-cost, compact, and efficient Cr(3+):LiCaAlF(6) (Cr:LiCAF) laser that is broadly tunable in the near infrared (746-887 nm) and blue/ultraviolet (375-433 nm) regions of the optical spectrum. The pump source is a 660 nm single-mode-diode with 145 mW of output power. A melt-grown Cr:LiCAF crystal with an extremely high figure of merit above 2000 was used as the gain medium. This enabled the construction of a high-Q-cavity with continuous wave (cw) lasing thresholds as low as 3 mW, slope efficiencies as high as 54%, and output powers up to 63 mW. The stored intracavity power levels were above 30 W. By placing a beta-barium-borate crystal at a second intracavity focus, we could obtain tunable cw blue/ultraviolet radiation with output powers up to 3.5 mW around 400 nm. When mode-locked using a saturable Bragg reflector around 800 nm, the Cr:LiCAF laser produced 95 fs pulses with average powers of 33 mW and peak powers of 3.58 kW at a repetition rate of 85.5 MHz. Extracavity second harmonic generation enables generation of femtosecond pulses around 400 nm. These results demonstrate the possibility to grow Cr:LiCAF crystals with passive losses below 0.15% per cm, which enables construction of low-cost and complexity systems that are pumped only with one low-power single-mode-diode.

Efficient continuous-wave TEM(00) and femtosecond Kerr-lens mode-locked Cr:LiSrGaF laser

Efficient high-power (900-mW) TEM(00) cw operation of a Cr:LiSrGaF laser pumped by a Kr(+) laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr(+)-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Properties of Cr:LiSrAIF(6) crystals for laser operation

We have performed several physical and optical measurements on the Cr:LiSAF (LiSrAlF(6)) laser material that are relevant to its laser performance, including thermal and mechanical properties, water durabilities, and Auger upconversion constants. The expansion coefficient, Young's modulus, fracture toughness, thermal conductivity, and heat capacity are all used to determine an overall thermomechanical figure of merit for the crystal. An investigation of the water durability suggests that the cooling solution should be maintained at pH = 7 to ameliorate problems associated with water dissolution. The Auger constant was found to become much more significant at higher Cr doping, in which excited-state migration leads to a substantial increase in the upconversion rate. We propose a design for a 50-W Cr:LiSAF laser system that is based on a detailed knowledge of all the relevant material parameters.