8. 2  Successful Operation of a High-Efficiency Green Laser for the Purpose of Pumping an Ultrashort Pulsed Laser
 

This picture, (20KB)

Fig. 8-3 Frequency conversion scheme using two nonlinear crystals with their optic axes arranged to be orthogonal Two nonlinear optical crystals are arranged with their optic axes orthogonal to one another. The converted output from the first crystal passes through the second crystal without interaction, and the unconverted laser beam in the first crystal will be converted in the second. This process can be repeated with the help of a half-wave plate, a quarter-wave plate, and two mirrors for the fundamental laser, resulting in a high total efficiency.

Fig. 8-4 High efficiency green laser output generation Conversion efficiency is greatly increased compared to conventional schemes. The high efficiency enables the use of low input laser intensity, which ensures that no photochromic damage occurs in the crystals.

---

The world's shortest-pulse 100 TW Ti:sapphire laser, which has been developed at JAERI, is pumped by a green second-harmonic laser following frequency conversion of a 1064 nm fundamental Nd:YAG laser pulse, using such a crystal as KTiPO4. Frequency conversion efficiency is about 50%. To make a compact Ti:sapphire laser with high output power, the laser system must have a high energy-conversion efficiency in order to provide second-harmonic output while remaining within the permissible input power limit to avoid damage to the crystals. We have proposed a new frequency scheme, arranging two nonlinear optical crystals in series with their optic axes orthogonal (four-pass quadrature arrangement). Thus, the second-harmonic output produced in the first crystal is not at the correct polarization for interaction in the second, and the input fundamental laser beam unconverted in the first can be reused for further frequency conversion in the second (Fig. 8-3). The process is repeated four times and finally, with the input fundamental laser (1064 nm, 607 mJ pulse, 10 Hz) having a power intensity of 76 MW/cm2, the generation of a 532 nm second-harmonic output laser pulse of 486 mJ has been achieved. This corresponds to an energy conversion efficiency of 80% (Fig. 8-4).

---

Reference H. Kiriyama et al., High Efficiency Second-Harmonic Generation in Four-Pass Quadrature Frequency Conversion Scheme, Opt. Commun., 174, 499 (2000).

Select a topic in left column

---

Persistent Quest - Research Activities 2001 Copyright(c) Japan Atomic Energy Research Institute