Takashi Arisawa

Lithium isotope separation by laser

A lithium isotope separation was performed using a laser isotope separation method. It was found that the lithium atoms with a natural isotopic abundance enhanced its6Li concentration up to over 90% by tuning the laser wavelength to the2P1/2 of6Li. Too high power, however, leads to a loss of enrichment due to the power broadening effect which was analysed by the equation of motion of density matrices.

RAY-TRACING MODEL FOR STRETCHER DISPERSION CALCULATION

We propose a ray-tracing model that provides a clear physical picture and simple formulas for grating pair stretcher dispersion calculations. With this model we can easily demonstrate why and to what extent the stretcher and compressor are opposite quantitatively without using a Fourier transform. The dispersion calculation shows that the spherical aberration in the stretcher decreases fourth-order dispersion compared with an aberration-free stretcher. In a chirped pulse amplification system, this fourth order can help to reduce residual fourth-order dispersion. The effect of the finite beam size and the misalignment are also considered.

Direct bonding of Ti:sapphire laser crystals

Direct bonding without the use of adhesive materials was demonstrated on a titanium-doped sapphire laser crystal with a bonding surface dimension of 12 mm x 6 mm(2). The bonding surfaces were treated with chemical processes to clean up and to create a hydrophilic (-OH) thin layer for hydrogen bonding. Two different processes of heat treatment performed in succession transformed the hydrogen bonding into direct bonding. The performance of the bonded crystal was tested by laser oscillation with the second harmonics of a Q-switched Nd:YAG laser at a 20-Hz repetition rate. In comparison with a normal laser crystal, there were no differences in output power or spatial profile in an input pumping condition of 30 mJ.

Diode-pumped 250-W zigzag slab Nd:YAG oscillator–amplifier system

A laser-diode-pumped zigzag slab Nd:YAG master oscillator power amplifier (MOPA) system featuring high pulse energy and high average power was developed for pumping of an ultrashort-pulse laser system. The MOPA system consists of an oscillator, a preamplifier, two postamplifiers, and image-relay telescopes. The postamplifiers have an angle-multiplexed ring-type double-pass configuration. A pulse energy of 1.26 J and an average power of 251 W were obtained at a repetition rate of 200 Hz. The frequency-doubled power when a LiB(3)O(5) crystal was used was 105 W at a repetition rate of 170 Hz. The intensity profiles of the fundamental and the second harmonic are nearly top-hat shaped and are suitable for pumping.

Ion Collection from Laser-Induced Plasma Using Positively Biased Wire Electrode

In atomic vapor laser isotope separation (AVLIS), an ion collection method which has a short collection time and low applied potential is required. We demonstrated that by using a positively biased wire electrode, the ions are collected from the laser-induced plasma in a shorter time at the same applied potential or at lower electric potential in the same collection times compared with the conventional parallel electrode method. The ion collection times could be estimated using simple one-dimensional models for both the wire electrode method and the parallel electrode method.

Characteristics of a pressure‐tuned single‐mode dye laser oscillator pumped by a copper vapor laser

Frequency tuning based on pressure control is demonstrated on an etalon-narrowed Littrow-type single-mode dye laser oscillator pumped by a copper vapor laser. The oscillator is installed in a pressure vessel and the frequency is scanned by controlling the refractive index of the air inside the vessel. To scan the dye laser frequency continuously without mode hopping, the cavity length is also controlled in addition to the pressure change. The frequency stability of the oscillator in a pressure vessel is within 100 MHz/1.5 hr and the oscillator can be scanned with a frequency range of 29 GHz at a scan rate of around 2.5 GHz/min.

Characteristics of high-power excimer laser master oscillator power amplifier system for dye laser pumping

Abstract A master oscillator power amplifier (MOPA) system using two XeCl lasers is constructed for pumping dye laser. The average power of 370 W, and the pulse energy of 740 mJ with the beam divergence of 0.5 mrad are obtained at the pulse repetition rate of 500 Hz. The energy extraction efficiency of the amplifier is nearly 90%. The amplification characteristics are analyzed by a rate equation with non-saturable loss, which results in the gain to loss ratio of around 100 for the amplifier.

Laser isotope separation of titanium by two-step photoionization

Titanium isotopes were selectively excited and photoionized using a two-step photoionization method, and the isotope separation was demonstrated, in which a separation factor of around 15 for50Ti was obtained. Spectroscopic parameters such as isotope shifts, photo-ionization cross section and excited state lifetimes were also measured. Isotope shifts up to 0.92 GHz were obtained for the transitions between 0 and 19938 cm−1 or between 170 and 20006 cm−1 among five isotopes. The cross section is 7.4×10−17 cm2 for the photo-ionization. The excited state lifetimes are 330±20 ns for 19938 cm−1, 260±15 ns for 20006 cm−1 and 250±15 ns for 20126 cm−1.

Nd:YAG oscillator–amplifier system with a passive ring self-pumped phase-conjugate mirror

A ring self-pumped phase-conjugate mirror with rhodium-doped barium titanate is used to correct aberrations in a laser-diode-pumped zigzag slab Nd:YAG oscillator-amplifier system. A diffraction-limited output of 360 mJ is achieved in a 36-ns pulse duration at a repetition rate of 100 Hz.

Highly excited odd-parity states of atomic gadolinium

An energy level survey of atomic gadolinium was performed in the 31 000 - region using simultaneous detection of optogalvanic and resonance photoionization signals; over 90 odd states, including 38 new ones, were revealed. The J-values of several new states were also determined by a method based on the J momentum selection rule.