Masaaki Yano

Single pulse switchout system for a passively mode‐locked Q‐switched Nd:YAG laser

A new optical switchout device for a passively mode‐locked Q‐switched laser is presented. This device can switch out a single pulse with energy at a preset level. The stability of the switched out single‐pulse energy is greater than the input pulse train. This is achieved by means of a high speed comparator and avalanche transitor chains. A single pulse of ±13% energy stability is obtained from the pulse train of our Nd:YAG laser oscillator with a ±25% fluctuation. The maximum repetition frequency of 2 kHz is sufficient not only for this kind of laser but also for other applications. The life of the avalanche transistors used here is more than one million shots. The possibility of further improvements in output stability is also discussed.

Development of a 1-kJ KrF laser system for laser fusion research

A l-kj KrF laser system under development is described. The system has an oscillator, three electron-beam (e-beam) amplifiers, and a Raman pulse compression system. The second stage e-beam amplifier has generated 170 J at the overall efficiency of 1.9%. The final stage amplifier is designed to deliver a 1-kJ optical output in 100 ns.

Actively Mode-Locked and Q-Switched YAG Laser with Precise Synchronizability

A system is described which generates synchronizable laser pulses with low temporal jitter (\lesssim30 ps). The conventional LC discharge pumping scheme is used. The laser is actively mode-locked by an A-O modulator and Q-switched by a Pockets cell. Pulses of various widths (200 ps~1 ns) can be obtained with the use of intra-cavity etalons and variation of the rf power to the A-O modulator. The stability of the pulse energy is very high (~3%).

Soft x-ray imaging by a commercial solid-state television camera

A commerical, solid‐state television camera has been used to record images of soft x radiation (0.8–12 keV). The performance of the camera is theoretically analyzed and experimentally evaluated compared with an x‐ray photographic film (Kodak direct exposure film). In the application, the camera has been used to provide image patterns of x rays from laser‐produced plasmas. It is demonstrated that the camera has several advantages over x‐ray photographic film.

Propagation profile of ablation front driven by a nonuniform UV laser beam

Spatial profile of ablation front is observed under the irradiation of spatially modulated 0.27‐μm laser beam. Propagation depth of the ablation front is derived by means of various methods which detect x‐ray radiation from aluminum substrates overcoated with polyethylene layers of different thicknesses. A higher mass ablation rate is observed for the UV laser than the longer wavelength lasers. However, observation with an x‐ray television camera shows that the spatial nonuniformity in the laser beam is projected on the ablation front surface without substantial smoothing.

Temperature Distribution Measurement of Laser Produced Plasma by X-Ray Photodiode Array

A multi-slit camera with an X-ray photodiode array has been developed to measure the electron temperature of a laser produced plasma. The fourth harmonic of Nd: glass laser output is irradiated on an aluminum plane target with a power density of 3×1014 W/cm2. The camera is set to view the plasma side. The profiles of X-ray intensity are obtained immediately. Using Abel inversion, the spatially resolved electron temperature distribution with 300 eV at the center is calculated by the absorption method assuming the Maxwellian distribution of free electrons.

High-density aluminum plasma produced by a picosecond KrF laser pulse

Experiments are reported in which a high-density aluminum plasma was generated by a 10-picosecond KrF laser pulse. The amplified spontaneous emission (ASE) level of the prepulse was controlled by using a saturable dye. The electron density was estimated from the intensity ration of the Ly-alpha satellite components. It is found that ASE has to be suppressed to less than 10 exp 9 W/sq cm to create a high electron density plasma.

Observation of living cells by x-ray microscopy with a laser-plasma x-ray source

We studied laser-produced plasma as an x-ray source for x-ray microscopy. Using water- window x rays, contact x-ray images of living sea urchin sperm were taken by a 500 picosecond x-ray pulse. The resist relief was examined by atomic force microscope and informations characteristic of x-ray microscopy were obtained. The finest feature noticed in the x-ray image was 0.1 micrometers .

Actively Mode-Locked and Q-Switched Phosphate Glass Oscillator

An actively mode-locked and Q-switched phosphate glass oscillator is studied. Observed pulse widths agree quite well with the active mode-locking theory. Stable and reproducible pulses of 100 ps to 2 ns are obtained. The pulses can be synchronized to external events with the precision of less than 30 ps. The single pulse energy is around 150 µJ. The stabilities of pulse width and pulse energy are 3% The oscillator operates at up to 4 Hz repetition rate.