Ultraviolet reflectometer

U L T R A ~ O L E T REFLECTOMETER AN O P E N - A I R , r o o m t e m p e r a t u r e m o n o c h r o m a t o r has been constructed around a Gaertner L-114 spectrometer. The reflectometer is intended for determ i n a t i o n of r o o m - t e m p e r a t u r e o p t i c a l c o n s t a n t s in t h e n e a r u l t r a v i o l e t r e g i o n of t h e s p e c t r u m . P r i n c i p a l p r o b l e m s in d e v e l o p i n g t h e s y s t e m ( s e e i l l u s t r a t i o n )

Lens~

difference is that a holographic plate records this i n t e r f e r e n c e p a t t e r n a s p e r m a n e n t c h a n g e s in i t s t r a n s m i s s i o n p r o p e r t i e s , p r o d u c e d by c h e m i c a l changes in the l i g h t - s e n s i t i v e s i l v e r c o m p o u n d on i t s s u r f a c e . With l i t h i u m n i o b a t e , the i n t e r f e r e n c e p a t t e r n i s r e c o r d e d a s a s e m i p e r m a n e n t c h a n g e in the i n d e x of r e f r a c t i o n t h r o u g h the t h i c k n e s s of the c r y s t a l and c a n be e r a s e d by h e a t i n g to 170°C.

Spectrometer Quartz Photomuttipiier rod Co|timator ~ \

Lamp

Lr~J GIo o pson ~ / / .... / . prism _ ' - - / t Diffuser Monochromotor Tetescope

w e r e the d e p o l a r i z a t i o n of l i g h t i s s u i n g f r o m m o n o c h r o m a t o r and t h e u n i f o r m i l l u m i n a t i o n of the p o l a r i z a t i o n p r i s m , so t h a t the a p e r t u r e of the s y s t e m w a s not c h a r g e d a s t h e p r i s m w a s r o t a t e d . Both p r o b l e m s w e r e o v e r c o m e by u s m g a l o n g q u a r t z r o d . Without t h i s r o d , t h e i n t e n s i t y of v e r t i c a l l y and h o r i z o n t a l l y p o l a r i z e d l i g h t c o m i n g f r o m the m o n o c h r o m a t o r d i f f e r e d by 20-30°/o, but u s e of t h e r o d s u b s t a n t i a l l y r e d u c e d t h i s d i f f e r e n c e . By p l a c i n g t h e p o l a r i z e r in f r o n t of t h e c o l l i m a t o r , and d i r e c t i n g t h e b e a m f r o m the q u a r t z r o d a l o n g t h e a x i s of the p o l a r i z e r , i n t e n s i t y c h a n g e s due to t h e r o t a t i o n of t h e p o l a r i z e r , but not a s s o c i a t e d with p o l a r i z a t i o n , w e r e m i n i m i z e d . P o l a r i z a t i o n d e p e n d e n c e of the p h o t o m u l t i p l i e r c o u l d be e l i m i n a t e d with an a l l o w a b l e i n t e n s i t y l o s s by u s i n g a diffuser. The most effective transducer was made by h e a t i n g a q u a r t z p l a t e to 125°C and a l l o w i n g it to cool. The i n s t r u m e n t i s b e i n g d e v e l o p e d by D. P o r t i g a l of Univac D i v i s i o n of S p e r r y Rand, P.O. Box 5100, P h i l a d e l p h i a , Pa. 19101, U.S.A.

The p h a s e m o d u l a t i o n of the l a s e r b e a m by t h e r e f r a c t i v e i n d e x v a r i a t i o n s of the c r y s t a l p r o d u c e s high r e c o n s t r u c t i o n e f f i c i e n c i e s b e c a u s e v i r t u a l l y none of the b e a m i s l o s t by a b s o r p t i o n and e f f i c i e n c i e s a s high a s 42% have b e e n o b t a i n e d with the new h o l o g r a p h i c m a t e r i a l , a s c o m p a r e d with e f f i c i e n c i e s of l e s s t h a n 6°/~ f o r c o n v e n t i o n a l h o l o g r a p h i c p l a t e s . T h i s w o r k i s d e s c r i b e d by J. T. L a M a c c h i a , F.S. Chen and D. B. F r a s e r in the D e c e m b e r 1968 i s s u e of A p p l i e d Physics Letters.

150cm INFRA-RED TELESCOPE CRYSTAL STORES 1000 HOLOGRAMS USING A SINGLE c r y s t a l of l i t h i u m n i o b a t e h o l o g r a p h ic r e c o r d i n g m a t e r i a l , d i f f e r e n t h o l o g r a m s have b e e n s t o r e d in t h i s c r y s t a l . In the e x p e r i m e n t s , a s i n g l e c u b i c a l c r y s t a l of l i t h i u m n i o b a t e i s p l a c e d on a r o t a t a b l e p l a t f o r m . F u n c t i o n i n g a s an o r d i n a r y h o l o g r a p h i c p l a t e , the c r y s t a l r e c o r d s the c o : n p l e x i n t e r f e r e n c e p a t t e r n s of l i g h t w a v e s a s one l a s e r b e a m s p l i t into two p a r t s , one of which s h i n e s d i r e c t l y on the c r y s t a l ( r e f e r e n c e b e a m ) . The o t h e r p a s s e s t h r o u g h a t r a n s p a r e n c y of the o b j e c t o r p a g e b e i n g s t o r e d (object b e a m ! and s t r i k e s the c r y s t a l . A f t e r the h o l o g r a m i s f o r m e d t h r o u g h t h e 1 - c m t h i c k c r y s t a l in one d i r e c t i o n , the c r y s t a l i s r o t a t e d a f r a c t i o n of a d e g r e e f o r e a c h new h o l o g r a m to be stored. Such a c r y s t a l c a n s t o r e h o l o g r a m s b e c a u s e a s u i t a b l y i n t e n s e l a s e r b e a m c a n f r e e enough e l e c t r o n s in the c r y s t a l to s e t up an i n t e r n a l e l e c t r i c f i e l d c a u s i n g o p t i c a l d a m a g e in the f o r m of a c h a n g e in r e f r a c t i v e index. The c h a n g e v a r i e s with the i n t e n s i t y of the l a s e r light a n d the c r y s t a l c a n r e c o r d i n t e n s i t y v a r i a t i o n s of a r e f e r e n c e b e a m i n t e r f e r i n g with an o b j e c t b e a m a s a c o n v e n t i o n a l h o l o g r a p h i c p l a t e d o e s . The

llO

Optics Technology

February 1969

I N F R A - R E D a s t r o n o m y c o u l d p r o v e to b e a s r e w a r d i n g a s r a d i o a s t r o n o m y . In p a r t i a l a c k n o w l e d g e m e n t of t h i s , t h e S c i e n c e R e s e a r c h C o u n c i l i s a w a r d i n g a g r a n t of £ 2 7 , 0 5 4 o v e r two y e a r s to t h e I m p e r i a l C o l l e g e of S c i e n c e and T e c h n o l o g y f o r a 150 c m i n f r a - r e d t e l e s c o p e and f o r p r e l i m i n a r y s t u d i e s f o r a l a r g e r i n s t r u m e n t . T h e p r o g r a m m e w i l l be m a n a g e d by a c o m m i t t e e u n d e r t h e c h a i r m a n s h i p of P r o f e s s o r J. Ring, and w i l l i n c l u d e r e p r e s e n t a t i v e s f r o m t h e main interested infra-red astronomy groups. The 1 5 0 c m - a p e r t u r e p a r a b o l o i d flux c o l l e c t o r w i l l be a t r a n s p o r t a b l e i n s t r u m e n t on a s i m p l e e q u a t o r i a l m o u n t and w i l l a l l o w o b s e r v a t i o n s to b e m a d e in the n e a r i n f r a - r e d and s u b - m i l l i m e t r e r e g i o n of the electromagnetic spectrum. D e c i s i o n s on a l a r g e r i n s t r u m e n t w i l l be t a k e n a f t e r e x p e r i m e n t s on the f e a s i b i l i t y of e q u a t o r i a l s i t i n g h a v e b e e n c o m p l e t e d with t h e 150cm t e l e s c o p e . The t e l e s c o p e w i l l be s h a r e d by i n f r a - r e d g r o u p s a t I m p e r i a l , Queen M a r y and U n i v e r s i t y C o l l e g e s of London U n i v e r s i t y and at E d i n b u r g h U n i v e r s i t y . B e c a u s e it w i l l be about a y e a r b e f o r e t h e t e l e s c o p e w i l l be in full u s e , an a r r a n g e m e n t h a s b e e n m a d e with t h e U n i v e r s i t i e s of M i n n e s o t a a n d C a l i f o r n i a to a l l o w UK a s t r o n o m e r s to h a v e i m m e d i a t e a c c e s s