Vladimir Krupkin

Nonimaging optics and solar laser pumping at the Weizmann Institute

The applicability of non imaging concentrators for solar thermal devices and laser pumping in a central receiver facility is discussed. A kilowatt scale solar pumped laser is described.

Excited-state absorption at 1.57 μm in U2+:CaF2 and Co2+:ZnSe saturable absorbers

Abstract Appreciable excited-state absorption (ESA) in U2+:CaF2 and Co2+:ZnSe saturable absorbers was measured at λ=1.573 μ m by optical transmission versus light fluence curves of 30–40 ns long pulses. The ground- and excited-state absorption cross-sections obtained were (9.15±0.3)×10−20 and (3.6±0.2)×10 −20 cm 2 , respectively, for U2+:CaF2, and (57±4)×10−20 and (12.5±1)×10 −20 cm 2 for Co2+:ZnSe. Thus, ESA is not negligible in U2+:CaF2 and Co2+:ZnSe, as previously estimated.

Visible solar-pumped lasers

Abstract We report on two visible solar pumped lasers; a red alexandrite laser with a potential tunability range between 700 and 818 nm, and a frequency doubled Nd:YAG laser operating at 532 nm. Highly concentrated solar energy was obtained by a 3-stage concentrator. An output power of up to 12 W was obtained from the alexandrite laser. The Q-switched Nd:YAG laser employed a type II KTP crystal for intracavity frequency doubling. Q-switching was obtained either passively or actively. In the passive Q-switching version, a water cooled Cr+4:YAG crystal was introduced into the laser cavity acting as both saturable absorber and laser rear mirror, and enforcing high repetition rate operation between 10 and 50 kHz. The average output power at 532 nm was 4.1 W. With an active acousto-optic modulator introduced between the laser rod and the high reflection rear mirror, the average output power at 532 nm and 7.3 kHz repetition rate was 8.7 W.

Solar-pumped Nd:Cr:GSGG parallel array laser

A compact, parallel array of three Nd:Cr:GSGG laser rods is used to construct a quasi-cw laser. The array is pumped by concentrated solar light and is mounted in a single solar concentrator. The three laser rods use a common pair of laser mirrors to define the optical resonator. The three laser beams are not coherently coupled in these experiments. The simplicity of the design, and its reasonable stability in terms of vibration and optical misalignment, suggest that the design may be scalable for higher power.

Coherent addition of two dimensional array of fiber lasers

Configurations for efficient free space coherent addition of four separate fiber lasers arranged in two dimensional array are presented. They include compact and robust interferometric combiners that can be inserted either inside or outside the cavity of the combined lasers system. The results reveal that over 85% combining efficiency can be obtained.

Single-mode-solar-pumped Nd:YAG ring laser

Single longitudinal mode solar pumped Nd:YAG ring cw and Q-switched lasers were simulated, built, and tested. The concentrator and laser designs, polarization control, and output coupling for cw and long pulse generation are presented. Laser pulses duration of 500 ns were measured supporting the single longitudinal mode operation with the linewidth of 2 MHz. This solar laser is proposed for remote sensing of the atmosphere from the outer space, namely the global wind measurement.

Compound parabolical concentrator as pumping device for solid state solar lasers

Laser heads based on two and three dimensional nonimaging concentrators were built and tested. The ray tracing and experimental results for concentrators illuminated by imaging primary concentrators are presented. These concentrators are currently used for pumping of solid state lasers of five hundred watts of laser power.

Temperature effects in passively Q-switched Nd:YAG laser

Temperature variations affect pumping efficiency, spectroscopic properties of lasing ions, and physical parameters of the host material. A numerical model was developed for evaluation of multilevel solid-state lasers. The model accounts for atomic levels population variations during Q-switched pulse evolution and for temperature dependence of the lasing transition linewidth. Results of simulation of pulsed Nd:YAG laser are presented for various temperatures of the laser crystal. The results of the simulation are compared with experimental results obtained using a Neodymium:YAG laser which is Q-switched by crystalline and organic saturable absorbers. The observed behavior of the lasers is in good agreement with the theoretical prediction.