We describe true continuous-wave (CW), high-power, line-narrowed, deep-ultraviolet (DUV) light sources for the high-resolution metrology tools such as wafer inspection and mask inspection systems. The 198.5-nm CW radiation with 300-mW power has also been achieved by sum-frequency mixing (SFM) of 1064-nm output from a single-frequency Yb<sup>3+</sup> fiber amplifier with the 244-nm radiation from a frequency-doubled argon-ion laser. The 266-nm CW DUV radiation with 5 W of maximum power has been generated by frequency doubling of 532-nm green laser output. Both sources utilize Brewster-cut CsLiB<sub>6</sub>O<sub>10</sub> (CLBO) crystal for efficient and stable DUV light generation.
In recent years, femtosecond laser processing of human hard/soft tissues has been studied. Here, we have demonstrated ablation etching of hydroxyapatite. Hydroxyapatite (Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>) is a key component of human tooth and human bone. The human bone is mainly made of hydroxyapatite oriented along the collagen. The micromachining of hydroxyapatite is highly required for orthopedics and dentistry. The important issue is to preserve the chemical property of the ablated surface. If chemical properties of hydroxyapatite change once, the human bone or tooth cannot grow again after laser processing. As for nanosecond laser ablation (for example excimer laser ablation), the relative content of calcium and phosphorus in (Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>) is found to change after laser ablation. We used here pulsewidth tunable output from 50 fs through 2 ps at 820 nm and 1 kpps. We measured calcium spectrum and phosphorus spectrum of the ablated surface of hydroxyapatite by XPS. As a result, the chemical content of calcium and phosphorus is kept unchanged before and after 50-fs - 2-ps laser ablation. We also demonstrated ablation processing of human tooth with Ti:sapphire laser, and precise ablation processing and microstructure fabrication are realized.
An ultra narrow line width of the F<SUB>2</SUB> laser, narrower than 0.2pm, is required for a CaF<SUB>2</SUB> only refractive optics exposure system. Also, a low peak laser power is needed for the extension of the optics lifetime. These ultra narrow line width and low peak power are achievable by long pulse duration. We, Association of Super-Advanced Electronics Technologies (ASET), are developing an ultra line narrowed F<SUB>2</SUB> laser below 0.2pm, with 5mJ high output energy, by adopting a 2-stage F<SUB>2</SUB> laser system, which consists of an oscillator and an amplifier. The oscillator for this 2-stage system is required to have an ultra narrow line width of below 0.2pm. We have developed F<SUB>2</SUB> laser with very long laser pulse duration of over 65ns (Tis: the integral squire pulse width), in a free running operation. And, by installing a line-narrowing module (LNM) in this F<SUB>2</SUB> laser, an ultra narrow line width of below 0.2 pm (FWHM, deconvolved) has been realized. This F<SUB>2</SUB> laser was successfully used for the oscillator of 2-stage system.
F<SUB>2</SUB> lasers are the light source of choice for microlithographic tools enabling structures below the 70 nm technology node. Accurate measurements of the spectrum of F<SUB>2</SUB> lasers are therefore very important. We have succeeded in measuring the spectrum of an ultra line narrowed F<SUB>2</SUB> laser using a VUV grating spectrometer calibrated with a 153 nm coherent light source (153CLS). As a first step in the development of a 157 nm coherent light source (157CLS), the less complex 153CLS has been built. Using resonant two-photon processes and four-wave mixing in Xe, this method provided a tunable laser system with high conversion efficiency and a very narrow linewidth, which can be approximated by a (delta) function. The 153CLS included a pulsed, single-mode tunable Ti:sapphire laser (768.0 nm), a third harmonic generation unit (256.0 nm) and an Xe gas cell. The 153CLS had a linewidth of 0.007pm (FWHM) and a power of 0.05mW at 1000 Hz. The VUV grating spectrometer and a Michelson interferometer for F<SUB>2</SUB> lasers have also been developed. The instrument function of the spectrometer has been measured with the 153CLS. Experimental and theoretical instrument functions were in good agreement (FWHM: 0.30pm). The instrument function at 157 nm was therefore estimated to have the theoretical FWHM of 0.31 pm. The spectral linewidth of the line-selected F<SUB>2</SUB> laser has been measured under various laser conditions with the spectrometer as well as with the interferometer. Results show good agreement between both measurements. The spectrum of the ultra line narrowed F<SUB>2</SUB> laser was measured with the VUV grating spectrometer calibrated using the 153CLS. The laser's FWHM of the deconvolved spectrum was 0.29pm. The deconvolved spectral purity containing 95% of the total laser energy is less than 0.84pm.
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, TEM<SUB>00</SUB> 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.
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.
The middle-infrared wavelength region around 3-5 m corresponds to the best optical laser band for high
atmospheric transmittance and eye-safety. Middle-infrared lasers are used in laser range finders, laser radars, and
so on. There are only a few reports on the atmospheric laser transmittance of these middle-infrared optical bands.
This paper describes, we believe for the first time, middle-infrared atmospheric transmittance characteristics as
measured by the second and third harmonics of tunable TEA-CO2 lasers.
The experimental results showed that the laser transmittance at 3.4 - 3.6 m correlated well with the results
calculated by the HITRAN-PC code, assuming a middle-latitude, summer condition. The measured transmittance
at 4.6 - 4.8 ,um exhibited a fine-structure, probably due to the absorption of atmospheric molecules such as NO2