S. Nakai

Nd-doped phosphate glass laser systems for laser-fusion research

Nd:phosphate laser glasses are evaluated in this paper as the active medium for high-power and high-energy laser systems for laser-fusion research. Small-signal gains and parasitic limits of rod amplifiers and disk amplifiers are first shown. Then system performances at a short-pulse, high-power regime and at a long-pulse high-energy regime are investigated. At a short-pulse regime, very high output power of 3.4 terawatts (TW) has been obtained because of the large stimulated emission cross section and the small nonlinear refractive index. At a long-pulse regime, we found that the effective saturation fluence of the phosphate glass LHG-8 is 4.0 J/cm2and we can efficiently extract the energy stored in the laser glass. This lead to the conclusion that Nd: phosphate glasses are very suitable for short-pulse as well as for long-pulse amplifications. In this paper, system descriptions and hardware specifications of the glass laser systems at the Institute of Laser Engineering (ILE), Osaka, University, are also briefly given.

The LEKKO VIII CO 2 gas laser system

The eight-beam CO 2 laser system, LEKKO VIII, producing 10 kJ for the inertial confinement fusion (ICF) research, has been completed. Advanced techniques developed with the LEKKO II 1 kJ laser have been fully implemented; such as a new type of laser gas, suppression of parasitic oscillation, and automatic operation of the system. A concept for a 100 kJ laser is examined as a feasible module design for a 1 MJ system.

Diode-Pumped Zig-Zag Slab Laser for Inertial Fusion Energy and Applications

A quasi-cw 290-kW diode-pumped zig-zag slab laser is being developed in order to demonstrate a concept of the IFE driver. Thermally managed amplifier has yielded a gain of 10, promising 10-J output at 10 Hz.

10J x 10 Hz Diode-pumped Nd: glass slab amplifier for inertial fusion energy

We have conceptually designed a diode-pumped Nd: glass slab amplifier module for Inertial Fusion Energy (IFE). As a first step of a driver development, we have been developing a diode-pumped zig-zag Nd: glass slab laser amplifier system which can generate an output energy of 10 J per pulse at 1053 nm in 10 Hz operation. The water-cooled zig-zag Nd:glass slab is pumped from both sides by 803-nm AlGaAs laser-diode (LD) module; each LD module has an emitting area of 420 mm x 10 mm and two LD modules generated in total 200kW peak power with 2.5kW/cm2 peak intensity at 10 Hz repetition rate. We have obtained in a preliminary experiment a 8.5 J output energy at 0.5 Hz with beam quality of 2 times diffraction limited far-field pattern.

High Power Ld Arrays For Pumping Solidstate Lasers

Remarkable features of the materials with reduced dimensionalities are that the coherent interactions between lightfield and matters become observable. Such interactions are the origin of the varieties of nonlinear optical responses which are interested not only in the fundamental point of view but also in the application fields such as ultrafast optical signal processing. One of the dye molecule pseudoisocyanine (PIC) makes self-assembled quasi-one-dimensional aggregates called J aggregates under the certain conditions. A coherence length of Frenkel excitons in PIC J aggregates is estimated to be nearly a hundred molecules from the nonlinear optical responses and the superradiant fluorescence decay. We have reported that PIC J aggregates show an extraordinary large NLO susceptibility, and also a novel excitation intensity dependent NLO response which is useful as an optical logic element. Characteristic features of the absorption spectrum of PIC J aggregates are the progression of the sharp transitions within the exciton band. They are located at 570 nm, 530 nm and 495 nm, respectively. The bands at 570 nm (called a J band) and at 495 nm are assigned to the transitions to the lower and to the upper band edges of exciton, respectively. The band at 530 nm is to the exciton coupled with optical phonons. In this report we propose novel efficient switching mechanisms of a perturbed free induction decay (FID) using different color pump pulses from probe pulses. These mechanisms are useful to control signal pulses with different color control pulses in ultrafast optical signal processing. The perturbed FID at J band of PIC J aggregates are investigated by a standard arrangement of a femtosecond pumpprobe method with the same or different pump and probe wavelengths in ethyleneglycol-water glass matrix at 77 K. We observed differential transmittance spectra (AT) around the J band exciting at each three band by changing the intensity of the pump pulses. The oscillatory structures are observed at the very early times when the probe pulses precede the pump pulses in each pump wavelength. These oscillations are assigned to the perturbed FID. The decay time of FID is similar in each pump pulse case and is about 300 fs. When the intensities of the pump pulses are increased over 30 pJ/cm2, a sharp dip appears in the middle of the central peak of the oscillation in AT spectra. This dip is the indicator of the pump saturating the transition to the exciton band (Rabi f l~pp ing) .~ The oscillations in AT have been attributed to the coherent coupling between the polarization at J band and the light field. Our FID results suggest that the transition to J band does not couple directly with the light field of different color pump pulses because there are no overlaps between J band and the light field at 530 nm and 495 nm. The coherent coupling may interact through the ground state depletion made by intense pump pulses. Further work to obtain a more detailed understanding is in progress.

High Efficiency Novel Eight Pass Laser-diode Pumped Nd:yag Zig-zag Slab Amplifier With Thermal Birefringence Compensation

5. S. Thosaki, H. Taniguchi, K. Tsujita, tripled, Q-switched Nd:YAG laser at 355 P8 B. Qevaraj, H. Inaba, Electron. Lett. 32, 1484 (1996). nm with -8-11s pulse duration and the pumping wavelength of 475 nm is chosen to match the absorption band of the RF solution. we investigated the emission High efficiency novel eight pass laser-diode Pumped Nd:YAG 2 ig -W slab amplifier with thermal birefringence compensation

Modification of Optical Transmission of flux-grown KTiOPO4 Crystal by Growth in Nitrogen Ambient

KTiOPO4(KTP) crystals have been grown by flux method in various ambients. A colorless KTP crystal was obtained in nitrogen ambient. It has been found that the absorption coefficient in the region from 400 to 550 nm depended on the oxygen concentration in the growth ambient. The strong correlation between the absorption coefficient and Pt impurity concentration suggests that the absorption of KTP crystal is attributed to incorporated Pt ions in the crystal.

Widely tunable efficient holosteric KTP optical parametric converter

photon absorption on the interaction fields simultaneously for the first time. At first, we calculate the conversion efficiency dependence on the input pump peak intensity under the same conditions as in our previous experiment with a 5 mm length KTP. The input pump pulse diameter is 90 pm, pulse width is 1.2 ps, and wavelength is 0.6 pm. The phasematching condition is a wavelength degenerate point (6 = 67.3, + = Oo). The results is shown in Fig. 1. The closed circles are the measured conversion efficiency from pump energy to the sum of signal pulse and idler pulse energies. The open circles are the measured transmittance of total energy. The solid lines are the calculated results. The calculated results coincide fairly well with our experimental results. By fitting to experimental results, we can obtain an second-order nonlinear coefficient and two-photon absorption coefficient of KTP as d,, = 4.2 pm/V and 0.35 pm/W respectively. Next, we calculate the conversion efficiency and autocorrelation pulse width dependence on the propagation distance (Fig. 2). The input pump pulse diameter is 100 pm, pulse width is 1.0 ps, and peak power density is 100 GW/cmZ (8.9 pJ). The results indicate that the maximum conversion efficiency of the parametric generation with a single KTP crystal is limited to about 10% regardless of the input pump intensity and crystal length due to saturation. We also find that due to the pulse narrowing effect, short pulses of 280 fs can be obtained from 1.0 ps pump pulses. In order to clarify the origin of the

Two-dimensional thermal stress-induced birefringence measurement in a laser diode pumped Nd:glass an

Ultralow-loss and high-reflectance mirrors were produced by Japan aviation electronics industry Ltd. whose characteristic was measured in precisely. To determine a mirror reflectance, we used the frequency response function measurement and the cavity decay-time measurement method (the ring-down method). As a result, a loss of 6 6 x includes scatter and absorption), a transmittance of 1399 i39 ppm, and reflectance of 99.8595 5 0.0033% were measured by the cavity decay-time measurement. A transmission efficiency qt = 99.14 f 0.86% can be calculated from the result. We found the transmission efficiency was 100% within the error. Reflected optical power is almost zero at the point of resonant frequency shown in Fig. 1. The loss measured here is the lowest at 1064 nm to our knowledge. The finesse was cross checked with measurement of frequency response function whose result is good agreement with the result of decay-time measurement. The high-transmission and high-reflectance mirror is possible to make an ideal FP cavity which used mode cleaner for the Gravitational wave antenna. Such mirrors will be one of the key technology not only for fundamental optical science but also for industrial applications. Center Research Laboratory Japan Aviation Electronics Industry Ltd., 1-1 Musashino 3-choume, Akinoshima Tokyo, Japan 1. 6 ppm (6

Effect of an ambient on the optical transmission of flux growth KTIOPO/sub 4/ crystals

The interest in borate crystals as a material for ultra-violet (UV) nonlinear optics (NLO) has been increased because all solid-state UV lasers obtained by NLO are strongly requested. The borate crystals, such as LiB305 (LBO) and P-BaB204 (BBO), have been used to obtain UV light by frequency-conversion of the Nd :YAG laser output. Recently, new UV NLO crystal with excellent UV NLO properties, cesium lithium borate, CsLiB,O,, (CLBO) has been found., In this work, we report on flux growth of large CLBO crystals and generation of 266 nm radiation by doubling the Nd : YAG laser output. The fifth-harmonic generations of the Nd:YAG laser output are also discussed. CLBO crystals were grown from the flux in a platinum crucible in a vertical cylindrical electric furnace by means of top-seeded Kyropoulos method. The starting charges were prepared from a mixture of Cs2C03, Li2C0, and B203 with ratio of 1 : 1 : 5.5. The estimated saturation temperature was 845°C. The growth temperatures were varied from 845°C to 843.5C with temperature decreasing of -O.lC/day CLBO crystal with dimensions of 13 X 12 X 10 cm3 was grown under this condition for 12 days. The weight of the crystal was 1.6 kg. This crystal exhibited well distinguishable facets. We did not find unstable growth, such as hopper growth whch has been often observed for LBO growth? although we did not optimize the growth conditions in our study. This indicates higher availability of large, high quality CLBO crystal compared with LBO and BBO. Table 1 illustrates the measured values of the NLO coefficient the angular and temperature bandwidths and calculated walk-off angle of CLBO for type-1 SHG at 532 nm. For comparison, values of BBO calculated from the refractive index data4 are included. Despite the smaller &, CLBO possesses smaller wak-off angle, larger angular and temperature bandwidths at 532 nm. These results imply that CLBO is suitable for 4 w generation of Nd :YAG laser output. By using CLBO crystal with length of 9 mm, we obtained more than 100 mJ output energy of 266