Testing of the durability of single-crystal calcium fluoride ...

Abstract

The transmission of uncoated and antireflection (AR)-coated CaF2 windows has been measured during long KrF laser exposures. Samples were tested for up to 75 million pulses in front of an industrial-grade KrF excimer laser at high repetition rates (200&#;300 Hz) and moderately high energy fluence (220&#;550 mJ/cm2). In this fluence range bare CaF2 performs much better than the best fused silicas currently available. Various AR coatings (whose structures were initially unknown to us) were deposited on CaF2 substrates polished to two distinct surface finishes. We determined the coating structures by using x-ray spectroscopy to identify positively all elements that were heavier than fluorine and fluorescence Rutherford backscattering spectroscopy to determine the layer structure and approximate layer thicknesses. We confirmed the structures by comparing measured UV transmission spectra with computer simulations. This study reveals excellent performance for SiO2/Al2O3/SiO2/Al2O3 coatings on highly polished substrates, which provided two-sided transmission in excess of 99.8% at 248 nm and no measurable deterioration after 75 million pulses. A MgF2/Al2O3 coating also performed quite well, while a hafnia-containing coating (MgF2/HfO2/LaF3) exhibited anomalous behavior. All-fluoride coatings consisting of MgF2/LaF3/MgF2 and MgF2/LaF3/AlF3 had good durability but lower starting transmission as a result of scatter losses in the LaF3 layer. These results demonstrate the availability of AR-coated CaF2 optics for high-power KrF laser applications with high transmission and no sign of degradation up to ~ 7 × 107 pulses.

Link to optec

© Optical Society of America

Vladimir Zvorykin, Radmir Gaynutdinov, Mikhail Isaev, Dmitry Stavrovskii, and Nikolai Ustinovskii
Appl. Opt. 59(5) A198-A205 ()

Ian M. Thomas
Appl. Opt. 27(16) - ()

Ming-Chung Liu, Cheng-Chung Lee, Bo-Huei Liao, Masaaki Kaneko, Kazuhide Nakahira, and Yuuichi Takano
Appl. Opt. 47(13) C214-C218 ()

F. Rainer, W. H. Lowdermilk, D. Milam, T. Tuttle Hart, T. L. Lichtenstein, and C. K. Carniglia
Appl. Opt. 21(20) - ()

S. Laux, K. Mann, B. Granitza, U. Kaiser, and W. Richter
Appl. Opt. 35(31) - ()

Want more information on calcium fluoride optics for high-power lasers? Feel free to contact us.

Cited By

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access Optica Member Subscription

Figures (19)

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access Optica Member Subscription

Calcium fluoride (CaF2or fluorite) is grown by vacuum Stockbarger technique in diameters of up to about 250mm.

Crystal for infrared use is often grown using naturally mined fluorite to reduce costs. It will not have the best transmission in the UV and VUV and can have absorption bands at 300nm due to impurities.

For UV and VUV applications chemically prepared raw material is generally used. For Excimer applications, we use only the highest grade of specially selected material and crystal.

For more information, please visit calcium fluoride optics for infrared applications.