- Email: [email protected]
Progress in holography
when he o u t l i n e d t h e i r w o r k on s e a l e d - o f f b e r y l l i a - t u b e a r g o n ion l a s e r s w h i c h h a v e shown l e s s than a 10% c h a n g e in output p o w e r o v e r 1000 h o u r s of o p e r a t i o n . T h e u s e of b e r y l l i a i n s t e a d of s i l i c a e n a b l e s an i n c r e a s e in o v e r a l l e f f i c i e n c y of a f a c t o r of f o u r w h i l e i t s m u c h h i g h e r t h e r m a l c o n d u c t i v i t y , r e s u l t i n g in a low w a l l t e m p e r a t u r e , r e d u c e s g a s c l e a n - u p to an i n s i g n i f i c a n t l e v e l . H a v i n g shown t h a t t h e t e c h n o l o g i c a l p r o b l e m s i n v o l v e d in t h e u s e of b e r y l l i a can be o v e r c o m e , and t h a t t h e t o x i c i t y i s w e l l b e l o w the p r e s c r i b e d s a f e t y l e v e l s when the c o r r e c t c o n d i t i o n s of u s e a r e a d o p t e d , the S E R L t e a m c l a i m t h a t the a d v e n t of t h i s tube w i l l not only i m p r o v e the u s e f u l n e s s and r e l i a b i l i t y of t h e a r g o n ion l a s e r , but w i l l a l s o p r o v i d e u s e f u l i m p r o v e m e n t s in m a n y o t h e r ion l a s e r s . It s e e m s v e r y l i k e l y t h a t t h e u s e of t h i s m a t e r i a l w i l l p r e s e n t m a n y a t t r a c t i o n s to the m a k e r s of c o m m e r c i a l l a s e r s and we s h o u l d e x p e c t to s e e it on the m a r k e t s h o r t l y . W h a t can a t b e s t b e d e s c r i b e d a s h i s s l i g h t l y s u r p r i s i n g w o r k in a t t e m p t i n g to u s e l a s e r s f o r m e a s u r ing s l a n t v i s u a l r a n g e a t a i r p o r t s w a s d e s c r i b e d by E. H i l l ( P l e s s e y ) . C o l o u r e d c a r t o o n s d e f i n i n g t h e v a r i o u s a e r o n a u t i c a l p a r a m e t e r s d i d not h i d e the f a c t t h a t a l t h o u g h such r a n g e m e a s u r e m e n t s a r e r e q u i r e d in t h e v i s i b l e r e g i o n , c o r r e s p o n d i n g with t h e p i l o t ' s sight, t h e P l e s s e y t e a m had u s e d a 900nm b a c k s c a t t e r s y s t e m with l i t t l e thought f o r t h e c o r r e l a t i o n of t h e i r r e s u l t s with t h e v i s i b l e c a s e . It w o u l d h a v e s e e m e d m o r e l o g i c a l to u s e , f o r i n s t a n c e , a l i t h i u m n i o b a t e f r e q u e n c y d o u b l i n g s y s t e m to c o n v e r t YAG l a s e r r a d i a t i o n into v i s i b l e r a d i a t i o n at 530nm.
Image up-conversion In the s e s s i o n on n o n - l i n e a r o p t i c s , an a t t r a c t i v e d e m o n s t r a t i o n of t h e t r a n s f o r m a t i o n of the b a s i c t h e o r y into r e a d i l y a p p r e c i a t e d e x p e r i m e n t w a s p r e s e n t e d by J . W a r n e r (Royal R a d a r E s t a b l i s h m e n t ) . U s i n g the p r i n c i p l e of s u m - f r e q u e n c y g e n e r a t i o n in a n o n - l i n e a r m a t e r i a l , he w a s a b l e to show the c o n v e r s i o n of 1 0 . 6 - p m CO 2 l a s e r r a d i a t i o n into v i s i b l e l i g h t . I m a g e u p - c o n v e r s i o n a r i s e s when an i n t e n s e p u m p s i g n a l ( f r o m a r u b y l a s e r ) i s i n c i d e n t on a s u i t a b l e c r y s t a l t o g e t h e r with an i n f r a r e d s i g n a l (in t h i s c a s e f r o m t h e CO 2 l a s e r ) . By f i l t e r i n g out the r a d i a t i o n t r a n s m i t t e d t h r o u g h the c r y s t a l at the p u m p w a v e l e n g t h , it i s p o s s i b l e to o b s e r v e an i m a g e of the i n f r a r e d s o u r c e a t the s u m f r e q u e n c y of the two s i g n a l s . In the RRE e x p e r i m e n t s , a s i n g l e c r y s t a l of P r o u s t i t e 12mm long and 8 m m in d i a m e t e r is u s e d a s t h e m i x e r , a n d t h e u p - c o n v e r t e d i m a g e , s h i f t e d by a b o u t 50nm f r o m the o r i g i n a l r u b y l a s e r w a v e l e n g t h , i s r e c o r d e d on p h o t o g r a p h i c f i l m . T h e t e c h n i q u e s h o u l d b e c a p a b l e of m i n i m u m d e t e c t a b l e p o w e r s of a b o u t 10 - s W, and u l t i m a t e p i c t u r e r e s o l u t i o n of about 150 x 150 r e s o l v a b l e e l e m e n t s . A t t e n d e d by 375 d e l e g a t e s f r o m 13 c o u n t r i e s t h e I E R E c o n f e r e n c e w a s d i s t i n g u i s h e d by s o m e v e r y efficient organisation.
R. H a w k i n s
Progress in holography H o l o g r a p h y Club M e e t i n g , L o u g h b o r o u g h , 21 A p r i l
D E V E L O P M E N T of g a s l a s e r s h a s o u t p a c e d that of p u l s e d l a s e r s a c c o r d i n g to J. W. G a t e s (NPL). T h i s i s p o s s i b l y b e c a u s e e a c h a p p l i c a t i o n of a p u l s e d laser calls for a widely differing specification resulting in a f r a g m e n t a t i o n of t h e d e v e l o p m e n t e f f o r t . If h o l o g r a p h i c r e s e a r c h w o r k e r s a g r e e d on a s p e c i f i cation for a pulsed laser, (possibly lower power l e v e l s of a few m i l l i w a t t s w o u l d s u f f i c e f o r m o s t w o r k ) m a n u f a c t u r e r s would b e a b l e to c o n c e n t r a t e t h e i r d e v e l o p m e n t e f f o r t and a u s e f u l h o l o g r a p h i c p u l s e d l a s e r m i g h t r e s u l t . An e x a m p l e of a r e c o n s t r u c t i o n f r o m a p u l s e d h o l o g r a m of an a e r o s o l s p r a y w a s d e m o n s t r a t e d by P . D ' V a z (I.R.D.). D. R e d m a n ( A . W . R . E . ) d e s c r i b e d t e c h n i q u e s and a p p l i c a t i o n s of h o l o g r a p h i c m u l t i p l e x i n g in r a d i o g r a p h y and u l t r a s o n i c d i a g n o s i s . T h e a b i l i t y to a s s e m b l e t w o - d i m e n s i o n a l v i e w s into a t h r e e - d i m e n s i o n a l i m a g e e n a b l e s the e x p e r i e n c e d r a d i o l o g i s t to l o c a t e o b j e c t s of i n t e r e s t m o r e a c c u r a t e l y . T h e r e s u l t s a r e d i f f i c u l t to i l l u s t r a t e on a p h o t o g r a p h , so a s i m p l e e x a m p l e of v e r t i c a l b a r s w a s i l l u s t r a t e d . S o m e d i s c u s s i o n of o t h e r t e c h n i q u e s f o r d i s p l a y i n g t w o d i m e n s i o n a l d a t a in t h r e e d i m e n s i o n s r e s u l t e d , but h o l o g r a p h i c t e c h n i q u e s a p p e a r to be m o r e v e r s a t i l e since intersecting planes are easily handled.
P r o f e s s o r G. W i l s o n ( P e n n s y l v a n i a State U n i v e r s i t y ) , who i s s p e n d i n g a s a b b a t i c a l y e a r at L o u g h b o r o u g h , s u m m a r i s e d t h e w o r k of s e v e r a l t e a m s in the U.S.A. on a c o u s t i c a l h o l o g r a p h y and d e s c r i b e d the w a t e r s u r f a c e t e c h n i q u e of v i s u a l i s i n g h o l o g r a m s , d e v e l o p e d by B. B. B r e n d e n ( B a t t e l l e N.W.). He c l o s e d by m e n t i o n i n g t h a t t h e r e w a s s o m e i n t e r e s t in the u s e of t h e P o h l m a n c e l l , but t h a t a s y e t the w o r k i s in an e a r l y stage. E. E. A l d r i d g e of ( A . W . R . E . , D i d c o t ) N. H. G. A l v e s (E.M.I.) and D. H o l t (B.A.C.) g a v e i l l u s t r a t e d s u m m a r i e s of t h e i r w o r k to d a t e in t h i s f i e l d . T h e wide v a r i e t y of r e c o r d i n g t e c h n i q u e s u s e d a r e of p a r t i c u l a r i n t e r e s t , A . W . R . E . u s i n g p u l s e d u l t r a s o u n d at 10MHz and a Mufax r e c o r d e r , B . A . C . u s i n g c o n t i n u o u s - w a v e u l t r a s o u n d at 1MHz and p h o t o g r a p h i c t e c h n i q u e s , and E . M . I . u s i n g p u l s e d u l t r a s o u n d in the r a n g e 500kHz --2MHz, and an o s c i l l o s c o p e d i s p l a y . T h i s t e c h n i q u e involves a scanning frame incorporating a pantograph. D r J. N. B u t t e r s a t t e m p t e d to i n t r o d u c e the s u b j e c t of c o n t o u r h o l o g r a p h y but few c o n t r i b u t i o n s w e r e f o r t h c o m i n g . It s e e m s t h i s i s a s u b j e c t which i s r e c e i v i n g r e l a t i v e l y l i t t l e a t t e n t i o n in the U.K. D. Holt
Optics Technology August 1969
215
Image up-conversion In the s e s s i o n on n o n - l i n e a r o p t i c s , an a t t r a c t i v e d e m o n s t r a t i o n of t h e t r a n s f o r m a t i o n of the b a s i c t h e o r y into r e a d i l y a p p r e c i a t e d e x p e r i m e n t w a s p r e s e n t e d by J . W a r n e r (Royal R a d a r E s t a b l i s h m e n t ) . U s i n g the p r i n c i p l e of s u m - f r e q u e n c y g e n e r a t i o n in a n o n - l i n e a r m a t e r i a l , he w a s a b l e to show the c o n v e r s i o n of 1 0 . 6 - p m CO 2 l a s e r r a d i a t i o n into v i s i b l e l i g h t . I m a g e u p - c o n v e r s i o n a r i s e s when an i n t e n s e p u m p s i g n a l ( f r o m a r u b y l a s e r ) i s i n c i d e n t on a s u i t a b l e c r y s t a l t o g e t h e r with an i n f r a r e d s i g n a l (in t h i s c a s e f r o m t h e CO 2 l a s e r ) . By f i l t e r i n g out the r a d i a t i o n t r a n s m i t t e d t h r o u g h the c r y s t a l at the p u m p w a v e l e n g t h , it i s p o s s i b l e to o b s e r v e an i m a g e of the i n f r a r e d s o u r c e a t the s u m f r e q u e n c y of the two s i g n a l s . In the RRE e x p e r i m e n t s , a s i n g l e c r y s t a l of P r o u s t i t e 12mm long and 8 m m in d i a m e t e r is u s e d a s t h e m i x e r , a n d t h e u p - c o n v e r t e d i m a g e , s h i f t e d by a b o u t 50nm f r o m the o r i g i n a l r u b y l a s e r w a v e l e n g t h , i s r e c o r d e d on p h o t o g r a p h i c f i l m . T h e t e c h n i q u e s h o u l d b e c a p a b l e of m i n i m u m d e t e c t a b l e p o w e r s of a b o u t 10 - s W, and u l t i m a t e p i c t u r e r e s o l u t i o n of about 150 x 150 r e s o l v a b l e e l e m e n t s . A t t e n d e d by 375 d e l e g a t e s f r o m 13 c o u n t r i e s t h e I E R E c o n f e r e n c e w a s d i s t i n g u i s h e d by s o m e v e r y efficient organisation.
R. H a w k i n s
Progress in holography H o l o g r a p h y Club M e e t i n g , L o u g h b o r o u g h , 21 A p r i l
D E V E L O P M E N T of g a s l a s e r s h a s o u t p a c e d that of p u l s e d l a s e r s a c c o r d i n g to J. W. G a t e s (NPL). T h i s i s p o s s i b l y b e c a u s e e a c h a p p l i c a t i o n of a p u l s e d laser calls for a widely differing specification resulting in a f r a g m e n t a t i o n of t h e d e v e l o p m e n t e f f o r t . If h o l o g r a p h i c r e s e a r c h w o r k e r s a g r e e d on a s p e c i f i cation for a pulsed laser, (possibly lower power l e v e l s of a few m i l l i w a t t s w o u l d s u f f i c e f o r m o s t w o r k ) m a n u f a c t u r e r s would b e a b l e to c o n c e n t r a t e t h e i r d e v e l o p m e n t e f f o r t and a u s e f u l h o l o g r a p h i c p u l s e d l a s e r m i g h t r e s u l t . An e x a m p l e of a r e c o n s t r u c t i o n f r o m a p u l s e d h o l o g r a m of an a e r o s o l s p r a y w a s d e m o n s t r a t e d by P . D ' V a z (I.R.D.). D. R e d m a n ( A . W . R . E . ) d e s c r i b e d t e c h n i q u e s and a p p l i c a t i o n s of h o l o g r a p h i c m u l t i p l e x i n g in r a d i o g r a p h y and u l t r a s o n i c d i a g n o s i s . T h e a b i l i t y to a s s e m b l e t w o - d i m e n s i o n a l v i e w s into a t h r e e - d i m e n s i o n a l i m a g e e n a b l e s the e x p e r i e n c e d r a d i o l o g i s t to l o c a t e o b j e c t s of i n t e r e s t m o r e a c c u r a t e l y . T h e r e s u l t s a r e d i f f i c u l t to i l l u s t r a t e on a p h o t o g r a p h , so a s i m p l e e x a m p l e of v e r t i c a l b a r s w a s i l l u s t r a t e d . S o m e d i s c u s s i o n of o t h e r t e c h n i q u e s f o r d i s p l a y i n g t w o d i m e n s i o n a l d a t a in t h r e e d i m e n s i o n s r e s u l t e d , but h o l o g r a p h i c t e c h n i q u e s a p p e a r to be m o r e v e r s a t i l e since intersecting planes are easily handled.
P r o f e s s o r G. W i l s o n ( P e n n s y l v a n i a State U n i v e r s i t y ) , who i s s p e n d i n g a s a b b a t i c a l y e a r at L o u g h b o r o u g h , s u m m a r i s e d t h e w o r k of s e v e r a l t e a m s in the U.S.A. on a c o u s t i c a l h o l o g r a p h y and d e s c r i b e d the w a t e r s u r f a c e t e c h n i q u e of v i s u a l i s i n g h o l o g r a m s , d e v e l o p e d by B. B. B r e n d e n ( B a t t e l l e N.W.). He c l o s e d by m e n t i o n i n g t h a t t h e r e w a s s o m e i n t e r e s t in the u s e of t h e P o h l m a n c e l l , but t h a t a s y e t the w o r k i s in an e a r l y stage. E. E. A l d r i d g e of ( A . W . R . E . , D i d c o t ) N. H. G. A l v e s (E.M.I.) and D. H o l t (B.A.C.) g a v e i l l u s t r a t e d s u m m a r i e s of t h e i r w o r k to d a t e in t h i s f i e l d . T h e wide v a r i e t y of r e c o r d i n g t e c h n i q u e s u s e d a r e of p a r t i c u l a r i n t e r e s t , A . W . R . E . u s i n g p u l s e d u l t r a s o u n d at 10MHz and a Mufax r e c o r d e r , B . A . C . u s i n g c o n t i n u o u s - w a v e u l t r a s o u n d at 1MHz and p h o t o g r a p h i c t e c h n i q u e s , and E . M . I . u s i n g p u l s e d u l t r a s o u n d in the r a n g e 500kHz --2MHz, and an o s c i l l o s c o p e d i s p l a y . T h i s t e c h n i q u e involves a scanning frame incorporating a pantograph. D r J. N. B u t t e r s a t t e m p t e d to i n t r o d u c e the s u b j e c t of c o n t o u r h o l o g r a p h y but few c o n t r i b u t i o n s w e r e f o r t h c o m i n g . It s e e m s t h i s i s a s u b j e c t which i s r e c e i v i n g r e l a t i v e l y l i t t l e a t t e n t i o n in the U.K. D. Holt
Optics Technology August 1969
215