Narayanan Srinivasan

Bandwidth Narrowing of an All-Solid-State Optical Parametric Oscillator Amplifier System

An all-solid-state narrow-bandwidth tunable near-infrared KTP optical parametric oscillator amplifier (OPOA) is presented. The bandwidth at 960 nm was reduced from the free running mode ( >100 GHz) to less than 150 MHz by the simultaneous injection seeding of the pump laser and the OPOA, which is close to the Fourier transform limit of the 4 ns output pulses. The OPOA has a potential tunability of over 60 nm from 915–975 nm determined by its external cavity grating tuned diode seed laser.

Efficient low-energy near-infrared KTiOPO(4) optical parametric converter.

We report a widely tunable near-infrared holosteric KTiOPO(4) optical parametric converter featuring a low pump energy threshold and high conversion efficiency. The converter uses two 10-mm-long crystals in a simple optical parametric oscillator amplif ier configuration and is tunable from 750 to 1040 nm for the signal. The pump energy threshold at 920 nm is 0.44 mJ for the 532-nm 8-ns 50-Hz input. The system produces as much as 0.45 mJ of energy at 920 nm with an external pump-to-signal energy conversion efficiency of 27% for pump inputs from just two times the threshold value. The internal pump-to-signal and idler energy conversion efficiency is estimated to be 58%. The low pump energy requirement of this system makes it compatible with small laser-diode-pumped solid-state lasers.

Temperature Dependence of Emission Cross-section of Yb:glass.

The temperature dependence of the emission cross-section of Yb (5 ×1020 atoms/cm3)-doped fluorophosphate glass has been investigated in the temperature range from 77 K to 380 K. The emission cross-section has been evaluated from the measured fluorescence spectra and the lifetime, using the Fuchtbauer-Ladenburg formula. A large change in the emission cross-section from about 0.6×10-20 cm2 at 380 K to 1.1×10-20 cm2 at 77 K was obtained by decreasing the temperature. The effect of reabsorption is found to be significant even at temperatures as low as 160 K which leads to underestimation of the emission cross-section values.

Thermal birefringence effect on the performance of a laser-diode pumped solid-state laser

We report the high-sensitivity measurements of two-dimensional (2D) thermal birefringence distribution in a laser-diode (LD) pumped Nd:glass (HAP4) laser under lasing (at 1054 nm) and under no lasing conditions. The thermal birefringence was reduced under the lasing condition owing to the depletion of stored energy by stimulated emission. By inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods, almost perfect birefringence compensation was achieved. The power loss due to thermal birefringence was evaluated quantitatively using the Jones matrix method. A considerable reduction of power loss, from over 12% before compensation to less than 0.4% after compensation, was observed. The output performance of this laser was in fairly good agreement with the estimation after taking into account the power loss due to thermal birefringence.

Tunable Near-Infrared and Visible All-Solid-State Optical Parametric Oscillator Amplifier System Based on Potassium Titanyl Phosphate Crystal

We present the design details and performance characteristics of a low-energy all-solid-state near-infrared optical parametric oscillator amplifier (OPOA). The pump source is a laser diode (LD) pumped frequency-doubled Nd:YAG laser with a single mode energy of 4 mJ in 8 ns, 50 Hz pulses. The OPOA system, based on potassium titanyl phosphate (KTP) crystal, features a low pump energy threshold at 532 nm of less than 0.4 mJ, broad tunability from 750 to 1040 nm for the signal and a conversion efficiency of 27% at 920 nm. External cavity second harmonic conversion of the idler to visible green-red light in a type II KTP crystal and of the signal to visible blue-green light in a type I BBO crystal was performed with efficiencies up to 10%. We have used the near-infrared output for wavelength-dependent fluorescence lifetime studies in ytterbium-doped laser materials. We have also used the second harmonic wavelengths between 565–600 nm to measure the transmission of Nd:YAG in a preliminary experiment to demonstrate the utility of the system.

Efficient KTP optical parametric oscillator amplifier and its applications

The design and construction of an efficient near‐infrared holosteric optical parametric oscillator amplifier based on KTiOPO4 (KTP) crystal are discussed. The system is tunable between 840 to 1451 nm and generates upto 0.45 mJ at 920 nm with 27% efficiency in 4–6 ns pulses. The 532 nm pump source is a frequency doubled LD pumped Nd:YAG laser producing upto 2 mJ in 8 ns, 50 Hz pulses. We have used the system to study the fluorescence lifetimes of a variety of Yb doped YAG and glass samples.

Widely tunable KTP optical parametric oscillator amplifier and its applications to fluorescence-lifetime measurement in Yb-doped laser materials

The design and construction of an efficient near-infrared holosteric optical parametric oscillator amplifier based on KTiOPO4 (KTP) crystal are reported. The system is tunable from 840 to 1451 nm and generates up to 0.45 mJ at 920 nm with 27% efficiency in 4 - 6 ns pulses. The 532 nm pump source is a frequency doubled laser-diode pumped Nd:YAG laser producing up to 2 mJ in 8 ns, 50 Hz pulses. We have used the system to study the fluorescence lifetimes of Yb:YAG and Yb:glass as a function of wavelength. The data reveal interesting variations in the reabsorption enhanced Yb-ion lifetime. Some Yb:YAG samples exhibiting a sharp increase in their lifetime near the peak absorption wavelengths. The longest lifetime measured in a few mm thick sample of Yb:YAG was 3.3 ms, which would be highly beneficial for energy storage applications using laser diodes.

Feasibility experiments on the laser-diode pumped solid-state laser for ICF Driver

An efficient laser‐diode (LD) array surface pumped Nd:YAG disk amplifier with an optical‐optical conversion efficiency of 12% was demonstrated. A double‐pass output energy of 67 mJ (input energy, 10 mJ) in a 1 ns pulse at 50 Hz rate was obtained. The two‐dimensional thermal stress‐induced birefringence in the disk amplifier was successfully measured using a newly designed polarimeter. An energy extraction efficiency of 65% was obtained which was well fitted to the Frantz‐Nodvik equations taking into account of the thermal birefringent loss.