Laser-induced dielectric breakdown and mechanical damage in silicate glasses

Abstract

S e n i o r Supervisor ( D r . J . C . 1rwin) Examining Committee (~r . K . S . ~i s w a n a t h a n ) Examining Committee ( D r . M . Hercher) E x t e r n a l Examiner PARTTAL COPYRIGIIT LICENSE I h e r e b y g r a n t t o Simon F r a s e r U n i v e r s i t y t h e r i g h t t o lend my t h e s i s o r d i s s e r t a t i o n ( t h e t i t l e o f which i s shown b e l o w ) t o u s e r s o f t h e Simon F r a s e r U n i v e r s i t y L i b r a r y , and t o make p a r t i a l o r s i n g l e c o p i e s o n l y f o r s u c h u s e r s o r i n r e s p o n s e t o a r e q u e s t from t h e l i b r a r y o f a n y o t h e r u n i v e r s i t y , o r o t h e r e d u c a t i o n a l i n s t i t u t i o n , on i t s own b e h a l f o r f o r one of i t s u s e r s . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r m u l t i p l e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y me o r t h e Dean of Graduate S t t l d i e s . I t is u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . T i t l e of T h e s i s /~i s s e r t a t i o n :A u t h o r :( s i g n a t u r e ) (name ) ( d a t e ) ABSTRACT D i e l e c t r i c breakdown and mechanical damage i n s i l i c a t e g l a s s e s under h i g h i n t e n s i t y l a s e r r a d i a t i o n i s i n v e s t i g a t e d l a t i v e magnitude of t h e e f f e c t proves t h a t t h e p h o t o c o n d u c t i v i t y does n o t r e s u l t from i o n i z a t i o n of sodium i n g l a s s as e x t e n s i v e l y quoted i n l i t e r a t u r e . The l i f e t i m e of t h e charge c a r r i e r s produced i s e s t i m a t e d t o be 1 0 -~s . From t h e r m o e l a s t i c c o n s i d e r a t i o n s a c r i t e r i o n f o r t h e v a l i d i t y of p o s s i b l e damage mechanisms i s e s t a b l i s h e d . It i s shown t h a t s t i m u l a t e d B r i l l o u i n s c a t t e r i n g cannot g i v e r i s e t o a n e f f e c t i v e a b s o r p t i o n of 50 em-' i n t h e f o c a l volume as r e q u i r e d by t h e t h e r m o e l a s t i c c o n s i d e r a t i o n s . It i s proposed and e s t a b l i s h e d t h a t t h e mechanical damage i s caused by t h e a c c e l e r a t i o n of p r i m a r y e l e c t r o n s produced by m u l t i p h o t o n i o n i z a t i o n , l e a d i n g t o a f u l l y developed e l e c t r o n i c i n s t a b i l i t y i n few nanoseconds. A t t h i s e l e c t r o n d e n s i t y t h e a b s o r p t i o n6 -i n t h e f o c a l volume i s 10 cm ', and i s r e s p o n s i b l e f o r t h e complete a b s o r p t i o n of t h e l a s e r p u l s e a t i n t e n s i t i e s above t h e t h r e s h o l d f o r breakdown. The d i f f u s i o n and recombination of e l e c t r o n s a r e found t o be n e g l i g i b l e , t h e o n l y r a t e l i m i t i n g process being the l o s s of e l e c t r o n energy...

Some Problems of Modeling the Volume Laser-induced Phase Transformations in Relaxed Optics

“…Nanovoids may be represented as results of the laserinduced laser-induce break-down and creation of cavitation bubbles [16 -19] too. The light pressure may be determined with help of next formula [3]…”

“…This method may be physical, chemical and physical-chemical [2] II. BASIC RESULTS AND DISCUSSIONS First system research of volume laser-induced phase transformations (breakdown and mechanical damage) in dielectrics (glasses) was realized by B. Sharma [3]. He selected basic peculiarities of interaction the laser irradiation with volume of solid.…”

“…Absorption of irradiation in focal volume. B. Sharma research the laser-induced breakdown in glasees, fused quartz and crystalline quartz [3]. He was possibility to measure the change of phoconductivity and other optical properties of irradiated matter.…”

Excitation of Periodical Shock Waves in Solid–State Optical Media (Yb:YAG, Glass) at SBS of Focused Low–Coherent Pump Radiation: Structure Changes, Features of Lasing

“…The evolution of profiles P(r) and n(r) after pumping was determined by unloading of the high-pressure region in the focal volume. A problem of unloading of a small cylindrical or spherical region in a solid-state optical medium, where the energy had been stored after ns laser pulse irradiation, had been considered in several studies (Bullough & Gilman, 1966;Conners & Thompson, 1966;Sharma & Rieckhoff, 1970). A typical process of relaxation is the propagation of an elastic dilatational wave across the medium.…”

Pulse duration dependence of laser damage mechanisms

“…It may be possible for an electron in the conduction band of a material to be accelerated by the laser field to an energy-greater than the band gap [1,14]. Each such electron would then be capable of exciting another electron into the conduction band by impact ionisation, leading to an exponential increase in the number of conduction electrons N. (10) where t' is the time required to accelerate an electron to the energy of the conduction band.…”