High Damage Threshold Optical Films for Excimer Lasers
- PDF / 341,813 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 3 Downloads / 188 Views
HIGH DAMAGE THRESHOLD OPTICAL FILMS FOR EXCIMER LASERS H.Ito, N.Kajita, Y.Minowa, H.Yoshida and T.Ina Mitsubishi Electric Corporation, Itami Works, Amagasaki, Hyogo, 661, Japan ABSTRACT High damage threshold coating for high energy KrF excimer laser has been developed by the multiple ion beam deposition system, which contains a couple of the ionized cluster beam (ICB) sources and the ionized gas beam source. The damage threshold of low refractive Si02, high refractive A1203 and Si02/A1203 multilayer coatings is found to be more than 105 shots at 8J/cm 2 laser energy. Oxidation is enhanced by ion bombardment during the film growth. The refractive indices of Si02 and A1203 films were 1.46 and 1.62 at the ion current density of 0.8g.A/cm 2 . The film density of SiOx approaches to the bulk Si02 of 2.3Og/cm 3 with increasing ion current density. The stress-free Si02 film can be obtained at the ion current density of around 0.5 iA/cm 2. INTRODUCTION Optical films for high power laser system must have high damage threshold and low absorption. The conventional optical coatings by electron beam deposition and Ar ion-assisted electron beam deposition methods limit the total energy of a laser system and size reduction of optics. The high laser damage threshold coatings offer several advantages of high power laser development not only in cost of optics but also in design of laser and optical system. We have been developing the ion beam deposition system to prepare higher damage threshold optical films. Low-energy ion bombardment during film growth can significantly improve physical properties. For example, low temperature epitaxy [1], high incorporation probabilities [2] and control of stoichiometries [3] have been reported. Several excellent films [4][5] have been prepared by the ionized cluster beam (ICB) method proposed by Takagi [6], which is one of the low-energy ion beam deposition method. Furthermore we have designed a long-lived ICB source [7], which will enable us to use a promising ICB technique for practical production of semiconductor and optical coatings. The advantages of using the ICB technique for low-temperature film growth include high-quality crystallization over even large misfit layers due to surface activation energy of cluster-ion bombardment and less damage due to lower impact energy per atom. In this article, the characteristics of the multiple ion beam deposition system and properties of high damage threshold films prepared by this deposition system are described.
Mat. Res. Soc. Symp. Proc. Vol. 236. 01992 Materials Research Society
518
EXPERIMENTAL Multiple ion beam deposition system and its characteristics
Fig 1. Schematic diagram of multiple ion beam deposition system, which contains a couple of ICB sources and ionized gas source
(cm-1
1.0 P/cm I
0 2.0
U,
. .
S1.8.
I
Stetchiorneirlc 5102
C 1.6 0-
E
-logo
0.
-1050
C.
"-1040
=
~1070 "*1060
- -- -- - ------------
0.5 WACM '
1.4
1.2
1010
"10'
-2 i -4 -71'0
-3 4
7 1'0'
Deposition Rate Rx ( X/min ) at a distance of 600mm f
Data Loading...
