Venkatesan Jambunathan

High-Contrast, High-Intensity Petawatt-Class Laser and Applications

A high-contrast high-intensity petawatt-class Ti:sapphire chirped-pulse amplification laser has been developed for research on high field science. A saturable absorber and a low-gain optical parametric chirped-pulse amplification preamplifier in the front-end have improved the temporal contrast in the system to ∼

CW lasing of Ho in KLu(WO 4 ) 2 in-band pumped by a diode-pumped Tm:KLu(WO 4 ) 2 laser

2 \times 10^{12}

Spectroscopic characterization of various Yb3+ doped laser materials at cryogenic temperatures for the development of high energy class diode pumped solid state lasers

on the subnanosecond time scale at the ∼70 TW power level. In addition to the high-contrast broadband high-energy output from the final amplifier has been achieved with a flat-top spatial profile with a filling factor of ∼70%. This is the result of pump beam spatial profile homogenization with diffractive optical elements. The system produces the uncompressed output pulse energy of 29 J, indicating the capability for reaching a peak power of ∼600 TW. We discuss in detail the design, performance, and characterization of the laser including output power, pulse duration, and spatiotemporal beam quality. We also describe the on-going upgrade of the laser system and some applications for the laser in relativistic dominated laser–matter interactions.

Q-switching of a Tm,Ho:KLu(WO4)2 microchip laser by a graphene-based saturable absorber

We demonstrate continuous wave (CW) room temperature laser operation of the monoclinic Ho(3+)-doped KLu(WO(4))(2) crystal using a diode-pumped Tm(3+):KLu(WO(4))(2) laser for in-band pumping. The slope efficiency achieved amounts to ~55% with respect to the absorbed power and the maximum output power of 648 mW is generated at 2078 nm.

Spectroscopic and lasing characteristics of Yb:YGAG ceramic at cryogenic temperatures

Precise values of absorption, emission and gain cross-sections of Yb:YAG, Yb:LuAG, Yb:CaF2 and Yb:FP15-glass at cryogenic temperatures are presented. To obtain the emission cross-sections two theoretical approaches were used. The first is the McCumber or reciprocity method (RM) which is based on the absorption spectra. The second is the Fuchtbauer-Ladenburg (FL) method using fluorescence spectra. From the results of cross-sections one can expect significant impact on laser performance on these materials especially in the case of high energy class diode pumped solid state lasers.

Graphene Q-Switched Compact Yb:YAG Laser

The first Ho microchip laser passively Q-switched using a graphene-based saturable absorber is demonstrated based on a Tm,Ho:KLu(WO4)2 crystal cut along the N g-axis. A maximum average output power of 74 mW is extracted from the diode-pumped laser at 2061 nm with a slope efficiency of 4%. Pulses as short as 200 ns with an energy of ~0.2 μJ are obtained at a repetition rate of 340 kHz. The energy transfer (ET), 3F4 (Tm3+) ↔ 5I7 (Ho3+) is studied, yielding ET parameters of P 28 = 1.69 and P 71 = 0.15 × 10−22 cm3 μs−1, revealing the strong prevalence of direct ET.

Continuous-wave laser generation at ~2.1 µm in Ho:KRE(WO 4 ) 2 (RE = Y, Gd, Lu) crystals: a comparative study

We present the spectroscopic characterization and continuous-wave laser operation of a new Yb doped Y3Ga2A13O12 (Yb:YGAG) ceramic material at cryogenic temperatures. The peak absorption is centered at 942 nm, zero phonon line at 970 nm and the peak emission at 1028 nm. The emission bandwidth is as much as three times larger than Yb:YAG at cryogenic temperatures which makes this material very promising for sub-picosecond pulse generation. At cryogenic continuous-wave laser operation, a maximum output of 2.92W with a slope efficiency of 20.3% at 60K is achieved.

Diode-Pumped Ho-Doped KLu(WO4)2 Laser at 2.08 µm

We describe a compact Yb:YAG laser Q-switched by a graphene-based saturable absorber and pumped by a laser diode at 932 or 969 nm. The compact laser generates a maximum average output power value of 185 mW at 1032 nm with a slope efficiency value of 12%. The shortest duration of the Q-switched pulse achieved is 228 ns at a repetition frequency of 285 kHz. The maximum pulse energy amounts to 0.65 μJ.

Microchip laser operation of Yb-doped gallium garnets

The laser performance of the monoclinic Ho:RE(WO4)2 (RE = Y, Gd, Lu) crystals is compared under identical experimental conditions. The comparison deals with the laser transition of Ho3+ at ~2.1µm by using two different pump sources, a diode laser operating at 1941 nm and a diode-pumped Tm:KLu(WO4)2 laser operating at 1946 nm. The results show internal slope efficiencies of ~60% and output powers exceeding 400 mW. The laser performance of Ho:KY(WO4)2 and Ho:KLu(WO4)2 is quite similar and superior to Ho:KGd(WO4)2.

Efficient laser performance of a cryogenic Yb:YAG laser pumped by fiber coupled 940 and 969?nm laser diodes

We report on the efficient continuous-wave diode-pumped laser operation of Ho in the monoclinic KLu(WO4)2 crystal at ~2080 nm, resonantly pumped at a wavelength of ~1941 nm by a fiber-coupled GaSb diode stack. A maximum output power of 408 mW and a slope efficiency of 54.5% with respect to the absorbed pump power were achieved. A comparison of the laser performance within the Ho-doped KRE(WO4)2 (Ho:KRE(WO4)2) family of monoclinic crystals showed a slightly superior performance of Ho:KY(WO4)2, achieving a maximum output power of 438 mW and a slope efficiency of 58.8% under identical conditions.