Technology And Application Of Large Meniscus Coating

Large areas diffractive optic plates (DOPs) have been widely used in inertial confinement fusion (ICF) systems, such as off-axis focusing beam sampling grating (BSG), color separation grating, pulse compress grating (PCG) and kinoform phase plate for spatial beam smoothing. The PCG is usually fabricated by holography lithography. In the process of fabrication, the uniformity of coated photoresist is a key factor which will influence the result of exposure and even the uniformity of PCG’s diffracting efficiency. The size of PCG which we plan to use in shengguang systems is more than 1000mm, which result in a serious problem that the technique of spin coating is unable to accomplish the task.The laser-induced damage threshold (LIDT) is a key parameter for BSG. The output coefficient may depress for the laser-induced damage, The BSG may injured for it. To get the high transmission efficiency of laser, Sol-gel derived silica antireflective (AR) coatings have been widely used as the optical components in high peak power laser systems which have excellent optical properties and high LIDT. But dip coating is not suitable for BSG because the thickness modulation along the longtitude. The main works of this thesis are focus on large area DOPs photoresist coating and sol-gel coating as follows:1. A simple meniscus coating system had been designed and established. Photoresist was coated on a 200 mm×200 mm substrate by the system. The photoresist thickness is calculated by analyzing the white light interference spectrum which were produced by the reflective light both on the top and at the bottom of the photoresist on the substrate. A thickness measurement system based on white light interference spectrometer was then installed to measure the thickness distribution of the coated photoresist.2. The relationship between photoresist thickness and scan velocity was experimentally explored. Aside from thickness, distribution uniformity of thickness was also important whicn was experimentally found as mainly dependent on system stability. First, the relationship between thickness uniformity and scan velocity was explored and optimized. Second, interspace variations in the scan process with different coating parameters is measured in situ using a non-contact laser triangulation sensor. Several variation reduction measures were also performed. After parameter optimization and systems improvement, the photoresist was uniformly coated with average 522nm and a peak-to-valley (P-V) value of 3% and root-mean-square deviation of 0.5% on a 200 mm×200 mm substrate.3. We assembled a larger meniscus coating system named " WYTJ-1500".And we analysed the mechanical structure of the system and then optimized it. In the view of the stabilization of the system, the linear motion actuator and actuating motors were installed in the system. A Laser Triangulation Sensor was installed for monitoring the distance between applicator and substrate all over the scanning. The deviation of the reservoir was up to the target position<5μm repeatability. An overturning platform was assembled for substrate. The substrate automatic return target successive approximation half adjustment method, and them a technological process was developed for the large scale meniscus coating system.We have used glasses to simulate the large area substrate. A lot of experiments were done to analyse the effects of the groove width on coating, liquid level bubble, stability and air gap regulating effects on coating uniformity. By controlling the distance changes between the applicator and substrate less than 30μm range, we completed the 1200 mm x 420 mm substrate photoresist coating for P-V deviation less than 5%.4. SiO2 sol-gel was coatted on glass by the sample meniscus coating system, and we observed and analyzed the result of coating. The influence of the change of decreased film coating thickness and groove depth on the BSG diffraction efficiency was researched by simulation calculation. Antireflective sol-gel was also coated on BSG to analyse the influence on diffraction efficiency.