Chapter 6 - Advanced Stimulated Brillouin Scattering for Phase Conjugate Mirror Using LAP, DLAP Crystals, and Silica Glass

HIDETSUGU YOSHIDA and MASAHIRO NAKATSUKA
Institute of Laser Engineering, Osaka University, Osaka 565-0871 Japan

6.1   INTRODUCTION

The stimulated Brillouin scattering (SBS) effect in various liquids and gases can be
applied to a phase conjugator [1, 2], as described in previous chapters. In SBS liquid
media such as heavy fluorocarbons [3–5] and tetrachlorides, it is necessary to
eliminate the dissolved impurities and solid microparticles, and these media must be
carefully handled due to their toxic properties. Quartz was used as a nonlinear
medium in the first practical demonstration of SBS in 1964 [6]. The first observation
of SBS in an optical fiber indicated that fiber provides highly reflective SBS due to
its long interaction length [7]. Long path lengths can produce SBS even at a low
incident power [8–11]. However, the incident pulse energy must be limited to a few
millijoules to avoid surface damage of the fiber.

Organic L-arginine phosphate monohydrate (LAP) was examined in 1983 at
Shangdon University, China as a nonlinear optical material [12]. LAP appeared to
be a promising material for laser fusion experiments as a replacement for potassium
dihydrogen phosphate (KDP) crystal [13, 14]. LAP and its deuterated analog,
DLAP, have some attractive properties for frequency conversion, such as a highly
nonlinear optical coefficient d_eff = 1.9 d_eff [KDP], a short-wavelength cutoff of
260 nm, and a less hygroscopic nature than that of KDP [15]. In addition, it has a
possibility of growing to a large dimension, greater than 100 × 100 × 100 mm³.

In a previous research the internal laser damage thresholds in LAP and DLAP
were measured using a 1053-nm Nd:YLF laser with 1- and 25-ns pulse widths and
were found to be much higher than for KDP and fused-silica glass [16]. The authors
could not explain this extremely high damage threshold at that time. Then they
observed intense stimulated Brillouin scattering (SBS) in LAP. This strong
scattering prevents the focus from reaching a high energy density and suppresses the
damage in the crystal. It also implies potential applications of SBS in phase
conjugate mirrors (PCM). The absolute Brillouin steady-state gain of DLAP was
reported to be the highest for the measured solid-state materials reported in the
literature [17]. Therefore we investigate the possibility that LAP and DLAP can be
used as a solid-state phase conjugator for high-power lasers.

In this chapter, we present the high SBS reflectivity in LAP and DLAP, using a
Nd:YAG laser, and we discuss hereafter their respective properties. Then we show
that these crystals can be used as phase conjugate mirrors in a laser. We demonstrate
the improvement of wavefront distortion induced by thermal effects in solid-state
laser materials. We also present the SBS properties of bulk fused-quartz glass at high
pulse energy operation.

HIDETSUGU YOSHIDA and MASAHIRO NAKATSUKA
Institute of Laser Engineering, Osaka University, Osaka 565-0871 Japan

6.1   INTRODUCTION

The stimulated Brillouin scattering (SBS) effect in various liquids and gases can be
applied to a phase conjugator [1, 2], as described in previous chapters. In SBS liquid
media such as heavy fluorocarbons [3–5] and tetrachlorides, it is necessary to
eliminate the dissolved impurities and solid microparticles, and these media must be
carefully handled due to their toxic properties. Quartz was used as a nonlinear
medium in the first practical demonstration of SBS in 1964 [6]. The first observation
of SBS in an optical fiber indicated that fiber provides highly reflective SBS due to
its long interaction length [7]. Long path lengths can produce SBS even at a low
incident power [8–11]. However, the incident pulse energy must be limited to a few
millijoules to avoid surface damage of the fiber.

Organic L-arginine phosphate monohydrate (LAP) was examined in 1983 at
Shangdon University, China as a nonlinear optical material [12]. LAP appeared to
be a promising material for laser fusion experiments as a replacement for potassium
dihydrogen phosphate (KDP) crystal [13, 14]. LAP and its deuterated analog,
DLAP, have some attractive properties...
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