Hitoshi Sekita

1.50-mum-band gain-shifted thulium-doped fiber amplifier with 1.05- and 1.56-mum dual-wavelength pumping

We propose and demonstrate a 1.50-mum- band gain-shifted thulium-doped fiber amplifier (TDFA) by using a novel dual-wavelength (1.05and1.56 -mum) pumping scheme for what we believe is the first time. By providing a small amount of 1.56-mum power to a conventional upconversion-pumped TDFA, we successfully demonstrated a small-signal gain larger than 25 dB and a noise figure of 5 dB in a 1475-1510-nm band.

High-power continuous-wave 3- and 2-/spl mu/m cascade Ho/sup 3+/:ZBLAN fiber laser and its medical applications

A new medical fiber laser oscillating at two useful wavelengths (3 and 2 /spl mu/m) is reported. We have demonstrated highly efficient and high-power continuous-wave cascade oscillation at room temperature with a holmium ion-doped fluoride glass fiber laser pumped with a 1.15-/spl mu/m fiber Raman laser. The simultaneous oscillation wavelengths were 3 and 2 /spl mu/m, and their combined output power was 3.0 W with a slope efficiency of 65%. To our best knowledge, this is the first achievement of watt-level-output power in the mid-infrared region with ZrF/sub 4/-BaF/sub 2/-LaF/sub 3/-AlF/sub 3/-NaF (ZBLAN) glass fiber. In experiments to evaluate potential for medical applications, we tested the two wavelength beam as a laser surgical knife on soft rabbit tissues and demonstrated that it had strong cutting capability, and that the coagulation layer thickness could be controlled by varying the power ratio of the two-wavelength laser.

Temperature dependence and optimization of 970-nm diode-pumped Yb:YAG and Yb:LuAG lasers

We have investigated the temperature dependence of output performances for 970-nm diode-pumped Yb:YAG (Yb(3+):Y(3)Al(5)O(12)) and Yb:LuAG (Yb(3+):Lu(3)Al(5)O(12)) lasers over the wide temperature range from 80 to 310 K. Temperature-optimized operation was experimentally demonstrated at around 160 K and was theoretically confirmed by taking into account the absorption spectra change of Yb crystals at low temperatures. Cooling the crystal to below 160 K caused a narrowing of the absorption bandwidth and led to a decrease in output power and efficiency.

Dual-wavelength continuous-wave cascade oscillation at 3 and 2 µm with a holmium-doped fluoride-glass fiber laser

We have demonstrated dual-wavelength continuous-wave oscillation at 3 and 2 mum with a Ho-doped ZrF(4)- BaF(2)- LaF(3)- AlF(3)- NaF fluoride-glass fiber laser by use of a cascade oscillation scheme. We have shown that the fiber laser operates with a high slope efficiency of 52% (at 3 and 2microm) with respect to the absorbed pump power. With a 6.5-m-long fiber we achieved an output power of 90 mW at each of the wavelengths that was limited only by the pump power, and the 3-microm output power is to our knowledge higher than any previously reported level with 3-mum Ho(3+) -doped fiber lasers.

Novel 1.50-μm Band Gain-Shifted Thulium-Doped Fiber Amplifier by using Dual Wavelength Pumping of 1.05 µm and 1.56 μm

We propose and demonstrate a 1.50-µm-band gain-shifted thulium-doped fiber amplifier (TDFA) by using a novel dual wavelength (1.05/1.56 µm) pumping scheme for the first time. By providing a small amount of 1.56-µm power to the conventional TDFA, we successfully demonstrated a small-signal gain of >25 dB and a noise figure of 5 dB in the 1475- to 1510-nm band.

High-power CW deep-UV coherent light sources around 200 nm based on external resonant sum-frequency mixing

We report pure continuous-wave (CW) high-power (>100 mW) deep-ultraviolet (DUV) light sources emitting around 200-nm spectral region based on singly resonant sum-frequency mixing (SRSFM). Efficient DUV generation is made possible by use of a Brewster-cut CsLiB/sub 6/O/sub 10/ (CLBO) crystal near noncritically phase-matched (NCPM) condition for the SFM of 1-/spl mu/m output of neodymium lasers. The CW radiation of fifth-harmonic wavelength of a neodymium laser at 213 nm was generated by the SFM of enhanced 1064-nm radiation with single-passing 266-nm radiation produced by external-resonant frequency doubling of a 532-nm green laser. With 1.8 W of 266-nm radiation incident upon a CLBO crystal, as much as 180 mW of CW 213-nm power has been produced. The sub-200-nm CW radiation with 140-mW power has also been achieved by SFM of 1064 nm with 244-nm radiation from a frequency-doubled Argon-ion laser in the CLBO crystal operated near the NCPM condition.

Laser-diode-pumped Nd:YAG active-mirror laser.

We describe a simple design, laser-diode-pumped cw Nd:YAG active-mirror laser and present a thermal analysis of the crystal. A cw output power of 2.4 W and an M(2) beam quality value of less than 1.9 at an incident pumping power of 8.9 W were obtained. From the thermal analysis we predict that the output power can be increased by increasing the pump beam diameter and the pump power at a constant excitation density.

Stable long-life 1-W femtosecond laser for industrial and biomedical applications

We have successfully developed a highly-stable commercial femtosecond laser. We achieved continuous operation of femtosecond laser over 4,000 hours.

1 PM SPECTRALLY NARROWED ARF EXCIMER LASER INJECTION LOCKED BY FOURTH HARMONIC SEED SOURCE OF 773.6 NM TI:SAPPHIRE LASER

We have achieved spectrum narrowing to 1 pm in a high‐power ArF excimer laser injection locked by an all solid‐state fourth harmonic (193.4 nm) seed source of 773.6 nm Ti:sapphire laser radiation. Superior laser properties such as sufficient output energy (90 mJ/pulse, 50 pps), locking efficiency exceeding 90%, wavelength drift less than 0.4 pm, and spectrum bandwidth fluctuation less than 0.2 pm were obtained, which meet the requirements for 1 Gbit dynamic random access memory microlithography.

CW DUV light sources for inspection tools

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 Yb3+ 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 CsLiB6O10 (CLBO) crystal for efficient and stable DUV light generation.