Yb KGW Laser Crystal
17 Jul 2019
Yb KGW Laser Crystal-has large absorption coefficient, low quantum defect, high absorption and emission cross section
The simple two-level electronic structure of the Yb ion avoids undesired loss processes such as upconversion, excited state absorption, and concentration quenching. Compared to the commonly used Nd:YAG crystal, Yb:KGW crystal has a much larger absorption bandwidth, 3 or 4 times longer emission lifetime in similar hosts with enhanced storage capacity, lower quantum defect and is more suitable for diode pumping than the traditional Nd-doped systems. The smaller Stokes shift reduces heating and increases the laser efficiency. In comparison with other Yb doped laser crystals such as Yb:YAG and Yb:YCOB crystals, Yb:KGW has a much higher (13-17 times) cross-section of absorption, lower quantum defect (~4%), a cross-section of emission that is 9 times higher than Yb: YCOB, and an emission band that is broader than Yb:YAG, a high nonlinear coefficient of refraction, and the highest slope efficiency (87%).
With the emergence of laser diode as the preferred pump source for inertial confinement fusion and the application and development of Yb3+ laser materials in communication and military, the research on Yb3+ laser materials will reach a climax. Yb3+: KGd(WO4)2 (Yb:KGW) is one of the most promising laser active materials. Yb:KGW crystal is expected to replace Nd:YAG crystal and Yb:YAG crystal in high power diode pumped laser system. Yb:KGW also has great potential for high power, short pulse time femtosecond lasers and their wide application.
1. The width of absorption line is wide, and the pump wavelength of LD pump source with phase matching can be obtained without strict temperature control;
femtosecond Yb:KGW laser applicated in nonlinear microscopy
Yb-ion based femtosecond lasers operating around 1000 nm are particularly suited for biological imaging with high-resolution multiphoton excitation fluorescence, and third and second harmonic generation microscopy. They are a good alternative to commonly used Ti:sapphire lasers emitting in the 800 nm wavelength regime. Longer excitation wavelengths are desirable due to lower scattering and higher penetration depths in the biological tissue. In addition, the autofluorescence and bleaching are also largely reduced. Furthermore, the generated third and second harmonics fall into the visible range (rather than UV), resulting in higher throughput and a simpler detection scheme. On the other hand, wavelengths in the range of a Cr:forsterite laser at around 1200-1300 nm suffer from significant water absorption. At higher excitation powers that may cause photo-damage of biological tissues. Moreover, direct diode pumping of Yb-ion doped laser gain media considerably reduces the cost of a system in comparison to Ti:sapphire and Cr:forsterite lasers, which are usually pumped by expensive solid-state or fiber lasers.
The extended cavity oscillators offer straightforward approach towards the scaling of the peak power by lowering the repetition rate (typically below 30-40 MHz).Nonetheless, the increased influence of the nonlinear effects usually results in a trade-off between the pulse duration and the peak power (or pulse energy). So far, pulses with 2.3 MW peak power (1 μJ energy) have been delivered from a 10 MHz Yb:KYW bulk oscillator. The pulse duration, however, was limited to 430 fs. Similarly, pulses with 1.3 MW peak power and 323 fs duration were generated from a 23.7 MHz Yb:CALGO bulk oscillator. On the other hand, short pulses with 145 fs duration but at a reduced peak power of 0.16 MW (24 nJ energy) were demonstrated directly from a 27 MHz Yb:CALGO bulk oscillator. Recently we demonstrated 67 fs pulses with 3 W of average output power at a repetition rate of 77 MHz from an Yb:KGW bulk oscillator.
Watt-level high-repetition-rate Yb:KGW regenerative amplifiers use acousto-optic switching. The obtained pulse energies up to now are on the order of tens of microjoules.