Photonic crystal resonators with the C4v symmetry were designed and fabricated on quantum cascade lasers with a strain-compensated multiple quantum well to achieve single-mode and vertical surface emission at 4.32 μm. Their fabrication accuracy was confirmed by high-resolution reflection spectroscopy. The maximum output power was 10 mW at 77 K. A far-field pattern with a small divergence angle below 1 degree was observed. Its main peak had a donut shape, which was attributed to the spatial symmetry of the resonance mode of the photonic crystal.

We quantified the thermal resistance of quantum cascade lasers (QCLs) using their structure functions and increased the laser output by employing ridge structures in which thermal resistance was reduced. To improve heat properties, three different QCL devices were prepared as follows. One was a device whose ridge was covered with SiO 2 , another was a device whose ridge was embedded with Au, and the other was a device whose ridge was embedded with Cu. The temperature distributions were measured with a thermoviewer and were analyzed with threedimensional simulations. From the results, improved heat dissipation by embedding the ridge was clarified. Furthermore, the structure functions obtained by static mode measurement suggested that the thermal resistance was improved from 9.3 to 6.5 K W −1 by embedding the ridge. As a result of the improvement, the QCL with the Au-embedded ridge had a 1.5-fold higher laser power than the QCL with the SiO 2 -covered ridge.

In-situ measurement of the transmittance change at 220 nm in synthetic silica glass under the ArF excimer laser irradiation showed three phenomenological stages: 1) initial coloring stage, 2) saturation stage where the coloring reaction equilibrates to the discoloring reaction and 3) heavy dosing stage where a rapid increase in photoabsorption occurs after an increase in the number of laser shots. The coloring rate at the initial stage depends only on the sum of the exposed laser power regardless of laser energy density, frequency and OH concentration. The concentration of OH in the glass reduces the photoabsorption at the saturation stage by increasing the extent of discoloring reaction while it scarcely influences on the number of shots at which the rapid photoabsorption occurs in the heavy-dose region.

The life of synthetic silica glass under ArF excimer laser irradiation was estimated in relation to the laser energy density by in-situ photoabsorption measurements under exposure to more than 107 shots. Dissolved hydrogen increases the life whereas OH in the glass scarcely influences it. Usual photomask glass is found to be tolerable to more than 1011 shots at 0.1 mJ/cm2 of laser irradiation intensity.

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