We present experimental results on the output power stabilization of an Ar+ laser for a direct laser writing system (LWS). Instability of the laser output power in the LWS cause resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. In this system, we have achieved the stability of ±0.20% for 12min and the relative intensity noise level of 2.1×10−7Hz−1∕2 at 100Hz. In addition, we applied our system to a 2mW internal mirror He–Ne laser. As a consequence, we achieved the output power stability of ±0.12% for 25min.

Most aspheric mirrors have been tested by the null lens or computer-generated hologram method. This approach, however, requires that the shape of the surface be similar to the target shape; otherwise testing may not be possible or correct. The Hartmann test has an advantage in that it has a larger dynamic range than a general interferometer, which means that the surface can be tested beginning at an early stage of the polishing process. We suggest use of the null Hartmann test in conjunction with a phase-shifting interferometer for the measurement of a 0.9-m aspheric concave mirror. This setup was able to measure the surface with a large surface form error as well as with a small error without sacrificing any measurement accuracy. Using this setup, we have successfully polished a surface to remove approximately 1 microm of peak-to-valley wave-front error of a total of 39 microm of error during 1 month of polishing.

Most aspheric surfaces have been tested by interferometer with some null correctors. This approach, however, often fails when there are many aspherical terms or test surface is very steep because it is not easy to design the conventional null lens or CGH (Computer Generated Hologram). On the other hand, 3-D profilometer can measure aspheric surfaces without any null correctors; however, it takes some time to measure, which makes it unsuitable for the production line in the factory. In this paper, we apply the Hartmann test to the measurement of steep convex aspheric surfaces of which diameter is about 16 mm. In order to increase the measurement accuracy, we calibrated the test setup using a CGH that simulates the ideal test surface. We demonstrated that the significant amount of error in the test setup could be removed by this calibration process. The test results showed only 2 nm rms WFE (wave front error) difference even though the WFE of test setup was worsened by more than 0.13 mum rms. Since this method makes it possible to measure highly aspheric surface quickly and accurately, it can be used in the production line.

Contrary to the academic interests of other existing studies elsewhere, this study deals with how the alignment algorithms such as sensitivity or Differential Wavefront Sampling (DWS) can be better used under effects from field, compensator positioning and environmental errors unavoidable from the shop-floor alignment work. First, the influences of aforementioned errors to the alignment state estimation was investigated with the algorithms. The environmental error was then found to be the dominant factor influencing the alignment state prediction accuracy. Having understood such relationship between the distorted system wavefront caused by the error sources and the alignment state prediction, we used it for simulated and experimental alignment runs for Infrared Optical System (IROS). The difference between trial alignment runs and experiment was quite close, independent of alignment methods; 6 nm rms for sensitivity method and 13 nm rms for DWS. This demonstrates the practical usefulness and importance of the prior error analysis using the alignment algorithms before the actual alignment runs begin. The error analysis methodology, its application to the actual alignment of IROS and their results are described together with their implications.

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