An edge illumination technique has been designed using a monochromatic light source that improves the identification of surface flaws on optics. The system uses a high-resolution CCD camera to capture images of the optics. Conventional edge illumination methods using white light sources have been plagued by light leaking around the optics causing high background levels. The background combined with lower resolution cameras has made it difficult to determine size and intensity characteristics of the flaws. Thus photographs taken of the optics are difficult to analyze quantitatively and do not allow for the detection of small, faintly illuminated sites. Infrared diodes have been utilized to illuminate large-scale (43 cm x 43 cm) fused silica optics, and a two-dimensional array CCD camera has been used to collect the image data. Flaw sizes as small as ~10 μm have been detected. A set of frames has been built to support the infrared sources where one diode array per side is magnetically attached to the frame. The diodes inject light into the optic causing the sites to illuminate, which can be detected by the camera. A customized mounting design has been implemented to secure the frames to the stage, or base, for image acquisition. The design uses a dual bracket assembly to support the frames. With this design for optical illumination, quantitative data has been obtained of the surface flaws. A comparison of the peak intensity, total integrated intensity and size of the flaws measured in these images and the size of the flaws as measured using a microscope will be presented.
We have developed techniques using small-beam raster scanning to laser-condition fused silica optics to increase their damage threshold. Further, we showed that CO2 lasers could be used to mitigate and stabilize damage sites while still on the order of a few tens of microns in size, thereby greatly increasing the lifetime of an optic. We recently activated the Phoenix pre-production facility to condition and mitigate optics as
large as 43 cm x 43 cm. Several full-scale optics have been processed in Phoenix. The optics were first photographed using a damage mapping system to identify scratches, digs, or other potential sites for initiation of laser damage. We then condition the optic, raster scanning with the excimer laser. The first scan is performed at a low fluence. A damage map is then acquired and any new damage sites or any sites that have grown in size are mitigated using the CO2 laser. The process is repeated at successively higher fluences until a factor of 1.7 above the nominal operating fluence is reached. After conditioning, optics were tested in a large beam 3ω laser and showed no damage at fluences of 8 J/cm2 average.
Using the Phoenix pre-production conditioning facility we have shown that raster scanning of 3ω optics using a XeF excimer laser and mitigation of the resultant damage sites with a CO2 laser can enhance their optical damage resistance. Several large-scale (43 cm x 43 cm) optics have been processed in this facility. A production facility capable of processing several large optics a week has been designed based on our experience in the pre-production facility. The facility will be equipped with UV conditioning lasers -- 351-nm XeF excimer lasers operating at 100 Hz and 23 ns. The facility will also include a CO2 laser for damage mitigation, an optics stage for raster scanning large-scale optics, a damage mapping system (DMS) that images large-scale optics and can detect damage sites or precursors as small as ≈15 μm, and two microscopes to image damage sites with ≈5 μm resolution. The optics will be handled in a class 100 clean room, within the facility that will be maintained at class 1000.
We establish that weak impulses can be effectively used to detect and image buried objects in disordered granular beds. The image carries information about the approximate shape of the surface of the buried object and its approximate location. Impulse backscattering can serve as a powerful tool to detect and to image the identity of buried metallic and non-metallic objects.
A discharge driven, dense plasma focus (DPF) in Neon has been developed at SRL as a point x-ray source for sub-micron lithography. This source is presently capable of delivering approximately 25 J/pulse of Neon K-shell x rays (8 - 14 angstrom) into 4 (pi) steradians with an approximately equals 1.4% wall plug efficiency at a 20 Hz repetition rate. This corresponds to 500 W of average x-ray power. The discharge is produced by a capacitor bank circuit (8 kV, 1.8 kJ) that drives approximately equals 320 kA currents into the DPF load, with approximately equals 1 microsecond(s) rise-times. X rays are produced when a dense pinch of Neon is formed along the axis of the DPF electrodes. Four X ten5 discharges using a cooled DPF head have been fired producing x rays. The variation in the measured x-ray output, over several 104 shots, corresponds to a variation in the dose delivered to a resist 40 cm from the source, of less than 1%. Data showing the measurement of the x-ray output, size, dose delivered to a resist, spectra of the source output, novel beam line concepts, and potential lithographic applications are discussed.
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