Kenshi Nakamura

Time-resolved electron density measurements in an ArF excimer laser discharge

Abstract The electron density in an ArF excimer laser discharge has been measured by means of a time-resolved optical interferometric method. By comparing the behavior of electron density in the absence of F 2 gas with that in the presence of F 2 gas, the dissociative attachment rate is estimated from graphical calculation.

Oscillation and gain characteristics of high power co-axially excited N2 gas lasers

Abstract A new type of co-axial discharge gas laser has been developed as a nitrogen laser, and the gain properties have been measured. The co-axial discharge tube consists of a ceramic pipe of inner diameter of 5 mm and length of 15 cm with two metallic electrodes at both ends. The excitation discharge was activated using a capacitor transfer circuit with a special pre-ionization discharge through the ceramic pipe. When the tube is used as an oscillator, an output laser energy of 0.45 mJ was obtained with pure N2 gas at pressure of 933 Pa (7 Torr). The time resolved gain measurement of N2 laser was made in the oscillator–amplifier configuration, and the value of the peak gain coefficient was estimated to 0.1 cm−1. The circuit analysis of the discharge circuit was also made to estimate discharge resistances, inductances and currents in the excitation circuit. The laser output increased up to 1.95 mJ at the charging voltage of 28 kV when the length and inner diameter of the discharge tube were increased to 30 cm and 9 mm respectively.

Ar2∗ excimer emission from a pulsed electric discharge in pure Ar gas

Abstract In order to investigate the possibility of laser action on the VUV Ar 2 ∗ excimer band in a pulsed electrical discharge, a discharge system which consists of four discharge units placed in a row on the optical axis has been designed. Strong emission in the VUV Ar 2 ∗ excimer band has been observed in the region 120 to 140 nm, and an optical gain of about 0.006/cm at 126 nm has been observed under the condition of Ar pressure of 3.5 atm and a charging voltage of 20 kV.

Optimization of the discharge characteristics of a laser device employing a plasma electrode

Discharge characteristics have been investigated of a laser device in which the surface‐discharge plasma from a dielectric surface is used as a preionizer and an electrode, the plasma electrode. It is demonstrated that a highly homogeneous discharge can be obtained by optimizing the delay time of the main volume discharge with respect to the surface discharge. The output energy from the device used as a N2 laser is also discussed.

Oscillation and gain characteristics of longitudinally excited VUV F2 laser at 40 Torr total pressure

Abstract The oscillation and gain characteristics of a longitudinally excited low-pressure F 2 laser in the Vacuum Ultra-Violet (VUV) region are presented for the first time. The low pressure, only 40 Torr (5.3 kPa) with 1.5% F 2 concentration, F 2 laser emits a VUV pulse of 18 ns duration from a ceramic tube 15 cm long and 5 mm inner diameter. Output energy of 140 μJ/pulse was obtained at a charging voltage of 20 kV and an excitation density of 2.3 MW / cm 3 . A time resolved gain measurement was achieved, and a peak gain coefficient of 13.5%/cm obtained. The delay time between the start of the discharge and the start of oscillation was the same as a N 2 laser. No red laser oscillation of atomic fluorine was observed.

Small-signal gain measurements in a discharge-pumped F2 laser

In a discharge-pumped F2 laser, time-resolved net-small-signal gain has been measured to study the population inversion by employing an oscillator-amplifier configuration. Characteristics of the gain and the fluorescence are studied under various conditions in two cases of He and Ne buffer gases. The peak of the net-small-signal gain in He/F2 and Ne/F2 show values of about 17%/cm and 9%/cm, respectively. The formation processes of the upper laser level F2(D′) are discussed on the basis of these experimental results.

Longitudinally excited N2 lasers without high-voltage switches

We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N(2) lasers (wavelength: 337 nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8 microJ and the efficiency was 0.16% at 18 Torr (2.4 kPa) when a slow-rising voltage pulse of -28 kV was applied (rise time: 21.3 micros). In the tandem-tube system, the laser output energy was 259.4 microJ and the efficiency was 0.11% at 18 Torr when a slow-rising voltage pulse of -48 kV was applied (rise time: 27 micros).

Longitudinally Excited N2 Laser Pumped by Lamplike Discharge

Nitrogen laser oscillation is observed in a lamplike discharge within a longitudinal excitation tube. The laser consists of a 30-cm-long Pyrex glass tube with an inner diameter of 2.5 mm and a step-up transformer directly coupled to the discharge tube without a high-voltage switch. The excitation is produced by wall-coupled discharge. The laser output energy is 1.7 µJ at 12 Torr (1.6 kPa) and 40 Hz when applying a slow-rising voltage pulse of 37 kV (rise time of 572 ns).

Time-resolved gain measurements in a KrCl laser

Abstract The oscillation characteristics of a discharge excited KrCl excimer laser has been studied experimentally for two different buffer gases, He and Ne. Optical gains were measured with nanosecond time-resolution, and compared with the experimental results on the breakdown voltage, the delay time of the laser oscillation with respect to the starting of discharge, and the pressure dependence of the laser output. The small signal gain coefficient was 0.056 cm -1 for the Ne buffer, while it was 0.041 cm -1 for the He buffer.

Comparison of modified driver circuit and capacitor-transfer circuit in longitudinally excited N2 laser.

We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct-drive circuit, for a longitudinally excited gas laser. The direct-drive circuit uses a large discharge impedance caused by a long discharge length of the longitudinal excitation scheme and eliminates the buffer capacitance used in the traditional capacitor-transfer circuit. We compared the direct-drive circuit and the capacitor-transfer circuit in a longitudinally excited N2 laser (wavelength: 337 nm). Producing high output energy with the capacitor-transfer circuit requires a large storage capacitance and a discharge tube with optimum dimensions (an inner diameter of 4 mm and a length of 10 cm in this work); in contrast, the direct-drive circuit requires a high breakdown voltage, achieved with a small storage capacitance and a large discharge tube. Additionally, for the same input energy of 792 mJ, the maximum output energy of the capacitor-transfer circuit was 174.2 μJ, and that of the direct-drive circuit was 344.7 μJ.