110-mJ 225-fs cryogenically cooled Yb:CaF_2 multipass amplifier

Abstract

Abstract:We report on a diode-pumped cryogenically cooled bulk Yb:CaF 2 12-pass amplifier delivering 110-mJ, 1030-nm pulses at a 50-Hz repetition rate. The pulses have a spectral bandwidth of 13 nm and are compressed to 225 fs pulse duration in a double reflection grating based compressor having a transmission efficiency of >90%. The measured output beam quality is M 2 <1.1. A key feature of the amplifier design is the 4f relay imaging onto the gain medium with progressive beam magnification for the mitigation of the spatial gain narrowing effect. The number of passes in the amplifier is scalable by increasing the size of imaging mirrors. In order to prevent accumulation of nonlinear phase due to self-phase modulation in air, the amplifier is enclosed into a low-vacuum case. Baltuška, "Free-space nitrogen gas laser driven by a femtosecond filament," Phys. Rev. A 86(3), 033831 (2012). 22. A.

Thermo-Optical Studies of Laser Ceramics

“…One of the options for solving these problems is to use a medium with a lower emission cross section than that of Yb:YAG to suppress the ASE effect and with a spectrum that enables operation at cryogenic temperatures. To date, the commonly used broadband media Yb:KYW, Yb:KGW, and Yb:CaF 2 working with ultrashort pulses [ 84 , 85 , 86 ] fit this description. However, in Yb:CaF 2 , the emission cross section is too small to efficiently extract the energy stored in the active element, and the thermal conductivity of Yb:KYW and Yb:KGW, that is lower than that of Yb:YAG, limits the average output power.…”

Multipass amplifiers with self-compensation of the thermal lens

“…The first is by changing the distance between the two lenses used for the imaging (see Fig. 1a) [18,39], so that their separation departs from 2f. To put it in another way, the distance between the focusing elements of the 4f-propagation can be adjusted to preserve the q-parameter also for a curved active medium [40].…”

“…The commonly used state-of-the-art multi-pass amplifiers are based on 4f relay imaging (4f) from active medium (AM) to active medium [16,17,18,19,20,21,22,24,25,23,15], so that in these amplifiers the beam proceeds as a succession of propagations…”

“…The 4f-design exhibits various advantages: It sustains equal beam size at each pass on the active medium independently of the dioptric power of the active medium and independently of the beam size at the active medium. Moreover, numerous passes can be realized with only a few optical elements [16,17,18,19,20,21,22,23,24,25,26]. Yet, this design does not represent the optimal solution for a multi-pass amplifier because the phase front curvature of the beam after propagation through this optical system depends strongly on variations of the active medium dioptric power.…”

A Yb:KGW dual-crystal regenerative amplifier

“…The Yb-ion has a long storage time, which is suitable for adopting a diode laser as a pump. Ytterbium-doped lasers have been developed to exhibit high pulse energy and power [13][14][15][16][17][18][19][20][21][22][23][24][25][26] .…”