Kyoichi Deki

High-power narrowband DUV laser source by frequency mixing in CLBO

We describe an all solid-state, high power, deep-UV (DUV) source based on sum-frequency mixing (SFM) of two single- frequency laser outputs. The system consists of a CW diode- pumped, Q-switched Nd:YLF laser operating at 1047 nm, a Ti:sapphire laser at 785-nm, and cascading SFM stages. Both laser sources are configured with an injection-seeded oscillator followed by amplifier to produce high power, single-frequency, TEM00 outputs. The third harmonic of Nd:YLF MOPA is mixed with the output from Ti-sapphire MOPA to generate the first UV, which is used for the second mixing with the residual fundamental output to generate the DUV radiation. CLBO crystal is employed for each SFM process. The system produced UV pulses at 241.6 nm with 3.4 W, and also DUV at 196.3 nm with 1.5 W of average powers at a 5-kHz pulse- repetition rate. The linewidth of the DUV output was measured to be less than 0.05 pm.

Superior Properties of Cesium Triborate CsB3O5 for 194 nm Light Generation with Nd:Y3Al5O12 Laser

We compared the 194 nm output energy of a type-I phase-matched CsB3O5 (CBO) with that of a type-II phase-matched CsLiB6O10 (CLBO) crystal. Using CBO crystal, we generated deep ultraviolet light at 194 nm by sum-frequency conversion of 2 µm band light and 213 nm light at a conversion efficiency of 2.2%. We found that the conversion efficiency obtained using CBO was 2.7 times higher than that obtained using CLBO at a maximum input of fundamental light. We concluded that CBO is a superior nonlinear optical crystal for generating 194 nm light with Nd:Y3Al5O12 lasers because of its larger spectral and angular acceptance.

Properties and applications of CLBO

Summary form only given. In this talk various information on the properties of CsLiB/sub 6/O/sub 10/ (CLBO) and the latest life test data at high repetition rate are provided for applications in reliable UV lasers.

Improvement of laser-induced surface damage in CsLiB6O10 crystal by ion etching

This paper investigates ion etching process to the surface of CsLiB6O10 (CLBO) crystal. Laser-induced surface damage was reduced and surface durability of CLBO crystal was improved by removing the subsurface embedded polishing compound. There was no surface degradation as a result of the ion etching. The effects of ion etching on surface damage were measured by a 1-on-1 test at a laser wavelength of 266 nm. Durability of the CLBO crystal was tested by the approximately 7 W fourth harmonic generated by a Nd:YAG laser. The durability of the ion etched surface was improved more than 10 times as compared with the as-polished surface.

Magnetic Field Tuning Dips in He–CdII and He–ZnII Hollow Cathode Lasers

The decay rates of the upper laser levels of He–CdII and He–ZnII lasers have been measured utilizing the magnetic field tuning dip, and the variations of these decay rates with He pressure are studied. The spontaneous decay rates of CdII and ZnII are estimated from the zero pressure intercept and found to be 58.1 MHz (4f2F7/2°, CdII, the upper level of 5378 A), 1.24 MHz (5s22D5/2, CdII, 4416 A), and 97.3 MHz (4f2F7/2°, ZnII, 4924 A). The variation of the decay rate of the upper laser level with metal source temperature is also studied with a He–CdII 4416 A hollow cathode laser and the difference of this variation between hollow cathode and capillary discharge lasers is discussed.

Design of a new technique for alleviating thermal dephasing of nonlinear optical crystal

A novel mechanism to alleviate the thermal dephasing of nonlinear optical crystal was developed. We named it temperature-profile compensation as defined from the in-situ temperature-profile measurement. Based on the concept of this mechanism, design on a technique for 3D temperature- profile compensation was demonstrated. By applying this technique on a CsLi B6O10 crystal, 10.6-W of 266-nm output power was obtained at 100-Hz. This result is 2.3-fold of that without alleviation. The conversion efficiency of 52 percent from the green is also more effective than the best result optimized at room temperature. Based on the similar concept, 1D temperature-profile compensation is also discussed for cases when the laser beam diameter reduced below approximately 2 mm. This is appropriate for frequency conversion of cw and diode-pumped kHz lasers. The design for 1D temperature-profile compensation can be very simple without involving any gas cooling.

Through-hole processing of aluminum nitride and silicon wafers using short-pulse lasers

Compact short pulse (200 - 350 ps) laser systems using SBS and SRS pulse compression techniques have been constructed. Fine processing of aluminum nitride and silicon wafer has been studied by using these laser pulses and compared with the results processed by 60 femto second laser system. Through-holes are formed on wafers by irradiation of the laser pulses, and the relationship between hole shapes and the processing conditions has been studied. The hole shape relates with the focusing length of the lens, laser fluence, pulse width and the wave length. Trepanning technique has been examined also to improve the hole shape. The result is quite.

Thermally stable third harmonic generation using type 1 LBO

Summary form only given. The third-harmonic light sources of Nd:YAG/YLF lasers have begun to be utilized for drilling via holes in print circuit boards according to the progress of high-density fabrication. Fast rise-time in burst mode operation and high pulse energy stability are required for the light source in this industrial use. Because of simple construction and less optical component requirement, type I SHG-type 2 THG(LBO) scheme has often been used for the third-harmonic generation. However it has unstable rise-time property in high average power operation. In the experiment the THG output was >5.6 W, and the phase-matching angle was tuned at the THG crystal temperature 50/spl deg/C and fixed constant through out the experiment. The upper waveforms show fundamental inputs operated at 5-kHz repetition frequency and the lower ones show the THG outputs at 49, 50, and 51/spl deg/C of the THG crystal temperature, respectively. As shown only +/- degree temperature offset causes elongated rise-time in THG output. The THG power absorption and accompanying self heating inside the THG crystal are considered to cause these disadvantages. The thermally induced phase mismatch is regarded to be comparable to the temperature bandwidth of the type 2 THG LBO crystal.

Efficient 10 W, high-quality, injection-seeded 262 nm generation using CLBO

Summary form only given. High-power, solid-state UV sources are of interest for industrial applications like precise machining, writing a grating into fibers, and so on. CsLiB/sub 6/O/sub 10/ (CLBO) has been used successfully for high-power fourth and fifth harmonic generation of Nd:YAG or Nd:YLF lasers. Efficient 10 W, 5 kHz, single-frequency 262 nm generation with TEM/sub 00/ quality was demonstrated by using a high-quality, 30 mm long CsLiB/sub 6/O/sub 10/ (CLBO) crystal. The source configured a temperature-elevated CLBO with low UV power density.

Watt-level DUV generation by solid state laser for lithography

The first all-solid-state laser system generating 1 W of 196 nm light at a 5-kHz pulse-repetition rate has been developed. The laser system consists of a Neodymium:Yttrium Lithium Fluoride maser oscillator power amplifier operating at 5 kHz, a single-frequency, gain-switched Titanium:sapphire laser, and additional frequency conversion stages utilizing nonlinear crystal such as Cesium Lithium Borate grown by USHIO and Lithium Triborate. The performance of each system component will discussed as well as the novel pathway employed to reach 196 nm.