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Visible laser oscillations from carbon monoxide
Volume 7, number 3
P HYSIC S L E T T E R S
d _1 d-/ =
e2c 2
82/d% fia+~o
(ck)2]-1
(4)
i a - ~o ×
1
]
1 - "r(l(,¢o)
,
15 November 1963
the relativistic case) depends on the plasma distribution function, an alteration of (2) will modify it. This will be discussed later on as well as the modification of the equation of motion as a consequence of Cherenkov emission; a single equation of motion contains both the radiation damping and the Cherenkov effect.
zm
A
A
w h e r e a l i e s a b o v e a l l s i n g u l a r i t i e s of the i n t e g r a n d . C o l l e c t i v e i n t e r a c t i o n s m o d i f y the f i e l d p r o p a g a t o r a n d i n t r o d u c e the t e n s o r
~'o(k, ~) = [~2-(ck)2]-1{~2[Sij-¢ij(k , oJ)]
(5)
(a)
(b)
- c 2kik 1 [6lj - ¢lj (k, ¢o)]} , w h e r e ¢/j(k, ~ ) i s t h e d i e l e c t r i c t e n s o r f o r an h o m o geneous isotropic collisionless relativistic plasma o b t a i n e d b y R u k h a d z e a n d S i l i n 8). If the p l a s m a i s n o n - r e l a t i v i s t i c , c.. r e d u c e s to t h e d i e l e c t r i c t e n s o r U o b t a i n e d b y G e r t s e n s h t e i n 3) a n d (4) b e c o m e s i d e n t i c a l w i t h the e n e r g y l o s s c o m p u t e d b y K o l o m e n s k i i 1, 2). The results obtained so far depend, even at ord e r e 2, on a n u m b e r of s i m p l i f y i n g a s s u m p t i o n s : p a r t i c l e m o v i n g a l o n g t h e d i r e c t i o n of the e x t e r n a l f i e l d (in o r d e r to e l i m i n a t e the b r e m s s t r a h l u n g a n d k e e p o n l y the C h e r e n k o v effect), h o m o g e n e o u s p l a s m a with i s o t r o p i c v e l o c i t y d i s t r i b u t i o n f u n c t i o n ( s e e (2)), n e g l e c t of t h e c o n t r i b u t i o n s of d i a g r a m s (b) in (4). H o w e v e r , the m e t h o d u s e d i s such that all these assumptions can be relaxed easily. T a k i n g into a c c o u n t a f a c t o r i s a t i o n t h e o r e m e s t a b l i s h e d b y R 6 s i b o i s 9), the c o n t r i b u t i o n of d i a g r a m s ~6) to the r h s of (4) w i l l c o n t a i n t h e t e n s o r [ ~ - ~ - * t w i c e . M o r e o v e r , a s t h i s t e n s o r (at l e a s t in
VISIBLE
LASER
OSCILLATIONS
Fig. 1. Contributions of o r d e r e2(e2C) n to the distribution function of particle A. We w i s h to thank P r o f e s s o r P r i g o g i n e who s u g g e s t e d t h i s p r o b l e m a n d w i t h whom we h a d m a n y valuable discussions. 1) A.A. Kolomenskii, Dokl.Akad. Nauk SSSR, 106 (1956) 982. 2) A. G. Sitenko and A. A. Kolomenskii, Soviet Phys. JETP, 3 (1956) 410. 3) M.E. Gertsenshtein, J . Exptl. Theoret. Phys. (USSR) 27 (1954) 180. 4) I. Prigogine, Non-equilibrium statistical mechanics (Lnterscience, New York, 1963). 5) R. Balescu, Statistical mechanics of charged particles (Interscience, New York) to be published. 6) A.Mangeney, Th~se, P a r i s (1963). 7) F. Henin, Physica, to be published. 8) A.A. Ruk_hadze and V. P. Silin, Soviet Phys. Uspekhi 5 (1962) 37. 9) P.RSsibois, Phys. Fluids 6 (1963) 817.
FROM
CARBON
MONOXIDE
L. E. S. MATHIAS a n d J. T. P A R K E R
Services Electronics Research Laboratory, Baldock, Hertfordshire, England Received 28 October 1963
A pulsed electrical discharge through carbon monoxide produces laser oscillations at numerous w a v e l e n g t h s in the r e d , o r a n g e , a n d g r e e n r e g i o n s of the s p e c t r u m . T h e o p t i c a l t r a n s i t i o n s b e l o n g to t h e A n g s t r i i m b a n d s y s t e m (BI~, - A1H) of the m o l e cule. T h e e x p e r i m e n t a l a r r a n g e m e n t w a s that d e s c r i b e d b y the a u t h o r s in r e f . 1). In t h e p r e s e n t e x p e r i m e n t s , 194
the mirror had 13-layer dielectric coatings. The i n n e r d i a m e t e r of the t u b e w a s 1 0 m m a n d t h e l e n g t h of the d i s c h a r g e 117 c m . T h e d i s c h a r g e w a s e x c i t e d b y high v o l t a g e dc p u l s e s having an a p p r o x i m a t e l y t r i a n g u l a r s h a p e . T h e r i s e t i m e w a s 0 . 5 / z s e c , the o v e r a l l l e n g t h 2 ~ s e c , a n d the r e p e t i t i o n f r e q u e n c y 25 c/s. The pulses were produced by a line-type pulse g e n e r a t o r t e r m i n a t e d b y a p u l s e t r a n s f o r m e r and a
Volume 7, number 3
PHYSICS
LETTERS
15 November 1963
Table 1 Wavelengths, relative intensities, and emission lines of the l a s e r o s c i l l a t i o n s . k * (A)
Relative Intensity **
Emission Line *** P(J), Q(J), R(J)
~. * (A)
Q~) Q(5) Q(6) Q(7)
6068.2 6065.7 6062.9
1 0.8 0.5
5603.8 5602.5 5600.4 5598.3 5596.0 5593.4 5590.6
0-3 Band 0.02 0.3 1 1 1 0.5 0.3
6613.5 6611.5 6609.1 6606.4 6603.1
0-5Band 0.02 0.2 0.4 1 0.7
6599.5 6595.5
0.3 0.06
Q(9) Q(10)
6074.2 6072.5 6070.5
0-4 Band 0.03 0.3 0.6
Q~) Q(5) Q(6)
P(13) or Q(8)
Relative
E m i s s i o n Line ***
Intensity **
PqJ), Q(J), R(J) Q(~ Q(~ Q(9) Q(5) Q(6) Q(7) Q(8) or R(13) Q(9) Q(10) Q(ll)
* This is the w a v e l e n g t h in a i r . The possible e r r o r is + 0.1 A. ** Intensities are g i v e n r e l a t i v e to the strongest o s c i l l a t i o n in each band. *** The emission line is specified by the branch to which it belongs, P, Q, or It.. and by the value of the quantum number J of the l o w e r rotational Ievel.
m a t c h e d r e s i s t i v e load. T h e i m p e d a n c e s of the l i n e a n d the l o a d w e r e 10 a n d 250 ~ r e s p e c t i v e l y . T h e e l e c t r o d e s of the t u b e w e r e c o n n e c t e d a c r o s s the load. Strong oscillations were obtained at gas p r e s s u r e s above 0.5 T o r r a n d at peak v o l t a g e s a b o v e 16 kV. T h e r e s u l t s r e p o r t e d h e r e w e r e o b t a i n e d at 2 T o r r a n d 30 kV. T h e peak c u r r e n t t h r o u g h the d i s c h a r g e was 80,~. T h e o s c i l l a t i o n s c o m m e n c e d 0.2 p s e c a f t e r the s t a r t of the c u r r e n t p u l s e t h r o u g h the d i s c h a r g e , a n d c e a s e d j u s t a f t e r the peak c u r r e n t w a s r e a c h e d . The t i m e b e t w e e n h a l f - p o w e r p o i n t s was 0.18 ~ s e c a n d the o v e r a l l d u r a t i o n ~ 0.4 ~ s e c . O s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s in t h r e e r a n g e s . P a i r s of m i r r o r s w e r e c h o s e n so that the output p o w e r o b t a i n e d with e a c h p a i r was e n t i r e l y or a l m o s t e n t i r e l y in one r a n g e only. Each p a i r c o m p r i s e d m i r r o r s with s t a g g e r e d b a n d w i d t h s a l l o w i n g o s c i l l a t i o n s to o c c u r in the o v e r l a p r e g i o n only. With one m i r r o r c o a t e d f o r a m a x i m u m r e f l e c t i v i t y at 6500 A a n d the o t h e r for a m a x i m u m r e f l e c t i v i t y at 7500 A, o s c i l l a t i o n s w e r e o b t a i n e d a t w a v e l e n g t h s in the r a n g e 6614-6595 A. T h e output b e a m had a n a v e r a g e p o w e r of 20 #W a n d a peak p o w e r ~ 4 W. With m i r r o r s c o a t e d f o r 6000 A a n d 7000 A, s t r o n g o s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s i n the r a n g e 6075-6062 A. Weak o s c i l l a t i o n s at w a v e l e n g t h s in the f i r s t r a n g e w e r e a l s o p r e s e n t . T h e output b e a m had a n a v e r a g e p o w e r of 40 pW and a peak p o w e r ~ 8 W. With m i r r o r s c o a t e d for 5200 A a n d 4800 A, o s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s in the r a n g e 5604-5590 A. T h e output b e a m had a n a v e r a g e p o w e r of 3.5 pW a n d a peak p o w e r
0.8 W. T h e b a n d w i d t h of e a c h m i r r o r to 10% t r a n s m i s s i o n p o i n t s w a s ~ 2000 A. T h e t r a n s m i s s i o n s of the t h r e e output m i r r o r s ( s e c o n d m i r r o r of each p a i r ) at the a p p r o p r i a t e o s c i l l a t i o n w a v e l e n g t h s w e r e 2, 6, a n d 1% r e s p e c t i v e l y . E a c h of the t h r e e output b e a m s w a s e a s i l y v i s i b l y to the eye. In e a c h c a s e , the i n t e n s i t y w a s u n i f o r m o v e r the c r o s s s e c t i o n a n d t h e r e w a s no apparent transverse mode structure. Objects p l a c e d in the b e a m s showed the u s u a l l a s e r s c i n t i l l a t i o n effects. With the t h r e e p a i r s of m i r r o r s s p e c i f i e d , at least seven oscillations were obtained at wavel e n g t h s in the r a n g e 6614-6595 A, at l e a s t s i x o s c i l l a t i o n s in the r a n g e 6075-6062 A, a n d at l e a s t s e v e n o s c i l l a t i o n s in the r a n g e 5604-5590 A. Each o s c i l l a t i o n s a t i s f i e d the c r i t e r i o n that r e m o v i n g the r e s o n a t o r m i r r o r b e t w e e n the d i s c h a r g e tube a n d the d e t e c t i o n s y s t e m s h o u l d r e s u l t i n a dec r e a s e in the output p o w e r at the w a v e l e n g t h c o n c e r n e d . The s t i m u l a t e d p o w e r w a s m e a s u r e d o v e r a s m a l l e r s o l i d a n g l e than w a s the s p o n t a n e o u s p o w e r . E v e n so, the d e c r e a s e in the c a s e of the s t r o n g e s t o s c i l l a t i o n in the f i r s t r a n g e w a s 2000: 1, in the c a s e of the s t r o n g e s t o s c i l l a t i o n in the s e c ond r a n g e , 8000: 1, a n d i n the c a s e of the s t r o n g e s t o s c i l l a t i o n i n the t h i r d r a n g e , 1000: 1. S p e c t o g r a m s t a k e n with a 21 ft c o n c a v e g r a t i n g i n s t r u m e n t showed t h a t the s t i m u l a t e d e m i s s i o n l i n e s w e r e c o i n c i d e n t with s p o n t a n e o u s e m i s s i o n l i n e s i n the 0-5, 0 - 4 , a n d 0-3 b a n d s of the ~ g str~lm s y s t e m . In p a r t i c u l a r , they w e r e c o i n c i d e n t 195
Volume 7, number 3
PHYSICS LETTERS
with the s t r o n g e s t l i n e s in each band. The w a v e l e n g t h s of the o s c i l l a t i o n s , the r e l a t i v e i n t e n s i t i e s of the o s c i l l a t i o n s in each w a v e l e n g t h r a n g e , and the e m i s s i o n lines a r e l i s t e d in t a b l e 1. The e m i s s i o n l i n e s w e r e i d e n t i f i e d f r o m the d a t a of C o s t e r and B r o n s 2) and Asundi 3). With a longer tube and m i r r o r s c o a t e d for 4800 A and 4600 A, at l e a s t four o s c i l l a t i o n s w e r e o b t a i n e d at wavelengths f u r t h e r in the g r e e n . The w a v e l e n g t h s w e r e not m e a s u r e d a c c u r a t e l y but w e r e in the r a n g e 5198-5186 A. At the s a m e t i m e , s t r o n g o s c i l l a t i o n s w e r e p r e s e n t at wavelengths in the r a n g e 5604-5590 A. The length of the d i s c h a r g e was 180 cm. It s e e m s p r o b a b l e that the s h o r t e r wavelength o s c i l l a t i o n s w e r e a s s o c i a t e d with t r a n s i t i o n s in the 0-2 band.
BY
15 November 1963
The a u t h o r s wish to thank C. A. P a r k e r of the Ad~miralty M a t e r i a l s L a b o r a t o r y for his c o - o p e r a tion in this work, and J. H. O l d i i e l d and D. L. Mack of the s a m e L a b o r a t o r y for a s s i s t i n g in taking the s p e c t r o g r a m s and for supplying the wavelength and r e l a t i v e i n t e n s i t y data in t a b l e 1. This l e t t e r is p u b l i s h e d by p e r m i s s i o n of the A d m i r a l t y .
References 1) L.E.S. Mathias and J. T. Parker, Appl. Phys. Letters 3 (1963) 16. 2) D. Coster and F. Brons, Physica 1 (1934) 634. 3) R. K. Asundi, Proc. Indian Acad. Sci. 3A (1936) 554.
INVESTIGATIONS ON M O V I N G S T R I A T I O N S MEANS OF PERIODICALLY PULSED IMAGE CONVERTER B. SAGGAU
Institut fdr Gasentladungstechnik und Photoelektronik, Technische Hochschule Stuttgart, Germany Received 31 October 1963
Hitherto p h o t o m u l t i p l i e r s and r o t a t i n g m i r r o r s 1-5) w e r e u s e d for o p t i c a l i n v e s t i g a t i o n s on moving s t r i a t i o n s in the p o s i t i v e c o l u m n of a g a s discharge. In g e n e r a l both m e t h o d s , e v e n t u a l l y c o m b i n e d with s p e c t r o s c o p i c m e a s u r e m e n t s , y i e l d s u f f i c i e n t i n f o r m a t i o n about light e m i s s i o n of the moving s t r i ations. The p o s s i b i l i t y to v i s u a l i s e the moving s t r i a t i o n s by m e a n s of r o t a t i n g m i r r o r s h o w e v e r i s l i m i t e d by the difficulty in s y n c h r o n i s i n g the m i r r o r r o t a t i o n by the s t r i a t i o n f r e q u e n c y . T h e s e d i f f i c u l t i e s a r e e s p e c i a l l y s e r i o u s , if the s t r i a t i o n f r e q u e n c y i s high or the light i n t e n s i t y of the s t r i a t i o n s is faint, so that the s y n c h r o n i s a t i o n m u s t be a c c u r a t e for a long t i m e of e x p o s u r e or f u r t h e r m o r e if the s t r i a t i o n s only a p p e a r for a s h o r t t i m e . T h i s happens on c e r t a i n c o n d i t i o n s a f t e r a s h o r t p e r t u r b a t i o n of the u n i f o r m c o l u m n ("wave of s t r a t i f i c a t i o n " 6)). In a l l t h e s e c a s e s our method of using a p u l s e d i m a g e c o n v e r t e r i s s u p e r i o r to the r o t a t i n g m i r r o r , b e c a u s e we do not n e e d any m e c h a n i c a l s y s t e m s . Fig. 1 shows the b l o c k d i a g r a m of the a r r a n g e ment and the f o r m s of the p u l s e s r e s p e c t i v e l y . The f i r s t s t a g e e l e c t r i c a l l y o r o p t i c a l l y p i c k s up i t s input s i g n a l f r o m the g a s d i s c h a r g e . T h e r e f r o m 196
the impulse f o r m e r p r o d u c e s the t r i g g e r p u l s e s for the phase stage, which for i t s p a r t is a b l e to dep h a s e the following pulses of "exposure". The d u r a -
I
....
I I
I
time of'exposure"I
j
n
1
H
Fig. 1. Block diagram of the device with the forms of the pulses respectively.
P HYSIC S L E T T E R S
d _1 d-/
e2c 2
82/d% fia+~o
(ck)2]-1
(4)
i a - ~o ×
1
]
1 - "r(l(,¢o)
,
15 November 1963
the relativistic case) depends on the plasma distribution function, an alteration of (2) will modify it. This will be discussed later on as well as the modification of the equation of motion as a consequence of Cherenkov emission; a single equation of motion contains both the radiation damping and the Cherenkov effect.
zm
A
A
w h e r e a l i e s a b o v e a l l s i n g u l a r i t i e s of the i n t e g r a n d . C o l l e c t i v e i n t e r a c t i o n s m o d i f y the f i e l d p r o p a g a t o r a n d i n t r o d u c e the t e n s o r
~'o(k, ~) = [~2-(ck)2]-1{~2[Sij-¢ij(k , oJ)]
(5)
(a)
(b)
- c 2kik 1 [6lj - ¢lj (k, ¢o)]} , w h e r e ¢/j(k, ~ ) i s t h e d i e l e c t r i c t e n s o r f o r an h o m o geneous isotropic collisionless relativistic plasma o b t a i n e d b y R u k h a d z e a n d S i l i n 8). If the p l a s m a i s n o n - r e l a t i v i s t i c , c.. r e d u c e s to t h e d i e l e c t r i c t e n s o r U o b t a i n e d b y G e r t s e n s h t e i n 3) a n d (4) b e c o m e s i d e n t i c a l w i t h the e n e r g y l o s s c o m p u t e d b y K o l o m e n s k i i 1, 2). The results obtained so far depend, even at ord e r e 2, on a n u m b e r of s i m p l i f y i n g a s s u m p t i o n s : p a r t i c l e m o v i n g a l o n g t h e d i r e c t i o n of the e x t e r n a l f i e l d (in o r d e r to e l i m i n a t e the b r e m s s t r a h l u n g a n d k e e p o n l y the C h e r e n k o v effect), h o m o g e n e o u s p l a s m a with i s o t r o p i c v e l o c i t y d i s t r i b u t i o n f u n c t i o n ( s e e (2)), n e g l e c t of t h e c o n t r i b u t i o n s of d i a g r a m s (b) in (4). H o w e v e r , the m e t h o d u s e d i s such that all these assumptions can be relaxed easily. T a k i n g into a c c o u n t a f a c t o r i s a t i o n t h e o r e m e s t a b l i s h e d b y R 6 s i b o i s 9), the c o n t r i b u t i o n of d i a g r a m s ~6) to the r h s of (4) w i l l c o n t a i n t h e t e n s o r [ ~ - ~ - * t w i c e . M o r e o v e r , a s t h i s t e n s o r (at l e a s t in
VISIBLE
LASER
OSCILLATIONS
Fig. 1. Contributions of o r d e r e2(e2C) n to the distribution function of particle A. We w i s h to thank P r o f e s s o r P r i g o g i n e who s u g g e s t e d t h i s p r o b l e m a n d w i t h whom we h a d m a n y valuable discussions. 1) A.A. Kolomenskii, Dokl.Akad. Nauk SSSR, 106 (1956) 982. 2) A. G. Sitenko and A. A. Kolomenskii, Soviet Phys. JETP, 3 (1956) 410. 3) M.E. Gertsenshtein, J . Exptl. Theoret. Phys. (USSR) 27 (1954) 180. 4) I. Prigogine, Non-equilibrium statistical mechanics (Lnterscience, New York, 1963). 5) R. Balescu, Statistical mechanics of charged particles (Interscience, New York) to be published. 6) A.Mangeney, Th~se, P a r i s (1963). 7) F. Henin, Physica, to be published. 8) A.A. Ruk_hadze and V. P. Silin, Soviet Phys. Uspekhi 5 (1962) 37. 9) P.RSsibois, Phys. Fluids 6 (1963) 817.
FROM
CARBON
MONOXIDE
L. E. S. MATHIAS a n d J. T. P A R K E R
Services Electronics Research Laboratory, Baldock, Hertfordshire, England Received 28 October 1963
A pulsed electrical discharge through carbon monoxide produces laser oscillations at numerous w a v e l e n g t h s in the r e d , o r a n g e , a n d g r e e n r e g i o n s of the s p e c t r u m . T h e o p t i c a l t r a n s i t i o n s b e l o n g to t h e A n g s t r i i m b a n d s y s t e m (BI~, - A1H) of the m o l e cule. T h e e x p e r i m e n t a l a r r a n g e m e n t w a s that d e s c r i b e d b y the a u t h o r s in r e f . 1). In t h e p r e s e n t e x p e r i m e n t s , 194
the mirror had 13-layer dielectric coatings. The i n n e r d i a m e t e r of the t u b e w a s 1 0 m m a n d t h e l e n g t h of the d i s c h a r g e 117 c m . T h e d i s c h a r g e w a s e x c i t e d b y high v o l t a g e dc p u l s e s having an a p p r o x i m a t e l y t r i a n g u l a r s h a p e . T h e r i s e t i m e w a s 0 . 5 / z s e c , the o v e r a l l l e n g t h 2 ~ s e c , a n d the r e p e t i t i o n f r e q u e n c y 25 c/s. The pulses were produced by a line-type pulse g e n e r a t o r t e r m i n a t e d b y a p u l s e t r a n s f o r m e r and a
Volume 7, number 3
PHYSICS
LETTERS
15 November 1963
Table 1 Wavelengths, relative intensities, and emission lines of the l a s e r o s c i l l a t i o n s . k * (A)
Relative Intensity **
Emission Line *** P(J), Q(J), R(J)
~. * (A)
Q~) Q(5) Q(6) Q(7)
6068.2 6065.7 6062.9
1 0.8 0.5
5603.8 5602.5 5600.4 5598.3 5596.0 5593.4 5590.6
0-3 Band 0.02 0.3 1 1 1 0.5 0.3
6613.5 6611.5 6609.1 6606.4 6603.1
0-5Band 0.02 0.2 0.4 1 0.7
6599.5 6595.5
0.3 0.06
Q(9) Q(10)
6074.2 6072.5 6070.5
0-4 Band 0.03 0.3 0.6
Q~) Q(5) Q(6)
P(13) or Q(8)
Relative
E m i s s i o n Line ***
Intensity **
PqJ), Q(J), R(J) Q(~ Q(~ Q(9) Q(5) Q(6) Q(7) Q(8) or R(13) Q(9) Q(10) Q(ll)
* This is the w a v e l e n g t h in a i r . The possible e r r o r is + 0.1 A. ** Intensities are g i v e n r e l a t i v e to the strongest o s c i l l a t i o n in each band. *** The emission line is specified by the branch to which it belongs, P, Q, or It.. and by the value of the quantum number J of the l o w e r rotational Ievel.
m a t c h e d r e s i s t i v e load. T h e i m p e d a n c e s of the l i n e a n d the l o a d w e r e 10 a n d 250 ~ r e s p e c t i v e l y . T h e e l e c t r o d e s of the t u b e w e r e c o n n e c t e d a c r o s s the load. Strong oscillations were obtained at gas p r e s s u r e s above 0.5 T o r r a n d at peak v o l t a g e s a b o v e 16 kV. T h e r e s u l t s r e p o r t e d h e r e w e r e o b t a i n e d at 2 T o r r a n d 30 kV. T h e peak c u r r e n t t h r o u g h the d i s c h a r g e was 80,~. T h e o s c i l l a t i o n s c o m m e n c e d 0.2 p s e c a f t e r the s t a r t of the c u r r e n t p u l s e t h r o u g h the d i s c h a r g e , a n d c e a s e d j u s t a f t e r the peak c u r r e n t w a s r e a c h e d . The t i m e b e t w e e n h a l f - p o w e r p o i n t s was 0.18 ~ s e c a n d the o v e r a l l d u r a t i o n ~ 0.4 ~ s e c . O s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s in t h r e e r a n g e s . P a i r s of m i r r o r s w e r e c h o s e n so that the output p o w e r o b t a i n e d with e a c h p a i r was e n t i r e l y or a l m o s t e n t i r e l y in one r a n g e only. Each p a i r c o m p r i s e d m i r r o r s with s t a g g e r e d b a n d w i d t h s a l l o w i n g o s c i l l a t i o n s to o c c u r in the o v e r l a p r e g i o n only. With one m i r r o r c o a t e d f o r a m a x i m u m r e f l e c t i v i t y at 6500 A a n d the o t h e r for a m a x i m u m r e f l e c t i v i t y at 7500 A, o s c i l l a t i o n s w e r e o b t a i n e d a t w a v e l e n g t h s in the r a n g e 6614-6595 A. T h e output b e a m had a n a v e r a g e p o w e r of 20 #W a n d a peak p o w e r ~ 4 W. With m i r r o r s c o a t e d f o r 6000 A a n d 7000 A, s t r o n g o s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s i n the r a n g e 6075-6062 A. Weak o s c i l l a t i o n s at w a v e l e n g t h s in the f i r s t r a n g e w e r e a l s o p r e s e n t . T h e output b e a m had a n a v e r a g e p o w e r of 40 pW and a peak p o w e r ~ 8 W. With m i r r o r s c o a t e d for 5200 A a n d 4800 A, o s c i l l a t i o n s w e r e o b t a i n e d at w a v e l e n g t h s in the r a n g e 5604-5590 A. T h e output b e a m had a n a v e r a g e p o w e r of 3.5 pW a n d a peak p o w e r
0.8 W. T h e b a n d w i d t h of e a c h m i r r o r to 10% t r a n s m i s s i o n p o i n t s w a s ~ 2000 A. T h e t r a n s m i s s i o n s of the t h r e e output m i r r o r s ( s e c o n d m i r r o r of each p a i r ) at the a p p r o p r i a t e o s c i l l a t i o n w a v e l e n g t h s w e r e 2, 6, a n d 1% r e s p e c t i v e l y . E a c h of the t h r e e output b e a m s w a s e a s i l y v i s i b l y to the eye. In e a c h c a s e , the i n t e n s i t y w a s u n i f o r m o v e r the c r o s s s e c t i o n a n d t h e r e w a s no apparent transverse mode structure. Objects p l a c e d in the b e a m s showed the u s u a l l a s e r s c i n t i l l a t i o n effects. With the t h r e e p a i r s of m i r r o r s s p e c i f i e d , at least seven oscillations were obtained at wavel e n g t h s in the r a n g e 6614-6595 A, at l e a s t s i x o s c i l l a t i o n s in the r a n g e 6075-6062 A, a n d at l e a s t s e v e n o s c i l l a t i o n s in the r a n g e 5604-5590 A. Each o s c i l l a t i o n s a t i s f i e d the c r i t e r i o n that r e m o v i n g the r e s o n a t o r m i r r o r b e t w e e n the d i s c h a r g e tube a n d the d e t e c t i o n s y s t e m s h o u l d r e s u l t i n a dec r e a s e in the output p o w e r at the w a v e l e n g t h c o n c e r n e d . The s t i m u l a t e d p o w e r w a s m e a s u r e d o v e r a s m a l l e r s o l i d a n g l e than w a s the s p o n t a n e o u s p o w e r . E v e n so, the d e c r e a s e in the c a s e of the s t r o n g e s t o s c i l l a t i o n in the f i r s t r a n g e w a s 2000: 1, in the c a s e of the s t r o n g e s t o s c i l l a t i o n in the s e c ond r a n g e , 8000: 1, a n d i n the c a s e of the s t r o n g e s t o s c i l l a t i o n i n the t h i r d r a n g e , 1000: 1. S p e c t o g r a m s t a k e n with a 21 ft c o n c a v e g r a t i n g i n s t r u m e n t showed t h a t the s t i m u l a t e d e m i s s i o n l i n e s w e r e c o i n c i d e n t with s p o n t a n e o u s e m i s s i o n l i n e s i n the 0-5, 0 - 4 , a n d 0-3 b a n d s of the ~ g str~lm s y s t e m . In p a r t i c u l a r , they w e r e c o i n c i d e n t 195
Volume 7, number 3
PHYSICS LETTERS
with the s t r o n g e s t l i n e s in each band. The w a v e l e n g t h s of the o s c i l l a t i o n s , the r e l a t i v e i n t e n s i t i e s of the o s c i l l a t i o n s in each w a v e l e n g t h r a n g e , and the e m i s s i o n lines a r e l i s t e d in t a b l e 1. The e m i s s i o n l i n e s w e r e i d e n t i f i e d f r o m the d a t a of C o s t e r and B r o n s 2) and Asundi 3). With a longer tube and m i r r o r s c o a t e d for 4800 A and 4600 A, at l e a s t four o s c i l l a t i o n s w e r e o b t a i n e d at wavelengths f u r t h e r in the g r e e n . The w a v e l e n g t h s w e r e not m e a s u r e d a c c u r a t e l y but w e r e in the r a n g e 5198-5186 A. At the s a m e t i m e , s t r o n g o s c i l l a t i o n s w e r e p r e s e n t at wavelengths in the r a n g e 5604-5590 A. The length of the d i s c h a r g e was 180 cm. It s e e m s p r o b a b l e that the s h o r t e r wavelength o s c i l l a t i o n s w e r e a s s o c i a t e d with t r a n s i t i o n s in the 0-2 band.
BY
15 November 1963
The a u t h o r s wish to thank C. A. P a r k e r of the Ad~miralty M a t e r i a l s L a b o r a t o r y for his c o - o p e r a tion in this work, and J. H. O l d i i e l d and D. L. Mack of the s a m e L a b o r a t o r y for a s s i s t i n g in taking the s p e c t r o g r a m s and for supplying the wavelength and r e l a t i v e i n t e n s i t y data in t a b l e 1. This l e t t e r is p u b l i s h e d by p e r m i s s i o n of the A d m i r a l t y .
References 1) L.E.S. Mathias and J. T. Parker, Appl. Phys. Letters 3 (1963) 16. 2) D. Coster and F. Brons, Physica 1 (1934) 634. 3) R. K. Asundi, Proc. Indian Acad. Sci. 3A (1936) 554.
INVESTIGATIONS ON M O V I N G S T R I A T I O N S MEANS OF PERIODICALLY PULSED IMAGE CONVERTER B. SAGGAU
Institut fdr Gasentladungstechnik und Photoelektronik, Technische Hochschule Stuttgart, Germany Received 31 October 1963
Hitherto p h o t o m u l t i p l i e r s and r o t a t i n g m i r r o r s 1-5) w e r e u s e d for o p t i c a l i n v e s t i g a t i o n s on moving s t r i a t i o n s in the p o s i t i v e c o l u m n of a g a s discharge. In g e n e r a l both m e t h o d s , e v e n t u a l l y c o m b i n e d with s p e c t r o s c o p i c m e a s u r e m e n t s , y i e l d s u f f i c i e n t i n f o r m a t i o n about light e m i s s i o n of the moving s t r i ations. The p o s s i b i l i t y to v i s u a l i s e the moving s t r i a t i o n s by m e a n s of r o t a t i n g m i r r o r s h o w e v e r i s l i m i t e d by the difficulty in s y n c h r o n i s i n g the m i r r o r r o t a t i o n by the s t r i a t i o n f r e q u e n c y . T h e s e d i f f i c u l t i e s a r e e s p e c i a l l y s e r i o u s , if the s t r i a t i o n f r e q u e n c y i s high or the light i n t e n s i t y of the s t r i a t i o n s is faint, so that the s y n c h r o n i s a t i o n m u s t be a c c u r a t e for a long t i m e of e x p o s u r e or f u r t h e r m o r e if the s t r i a t i o n s only a p p e a r for a s h o r t t i m e . T h i s happens on c e r t a i n c o n d i t i o n s a f t e r a s h o r t p e r t u r b a t i o n of the u n i f o r m c o l u m n ("wave of s t r a t i f i c a t i o n " 6)). In a l l t h e s e c a s e s our method of using a p u l s e d i m a g e c o n v e r t e r i s s u p e r i o r to the r o t a t i n g m i r r o r , b e c a u s e we do not n e e d any m e c h a n i c a l s y s t e m s . Fig. 1 shows the b l o c k d i a g r a m of the a r r a n g e ment and the f o r m s of the p u l s e s r e s p e c t i v e l y . The f i r s t s t a g e e l e c t r i c a l l y o r o p t i c a l l y p i c k s up i t s input s i g n a l f r o m the g a s d i s c h a r g e . T h e r e f r o m 196
the impulse f o r m e r p r o d u c e s the t r i g g e r p u l s e s for the phase stage, which for i t s p a r t is a b l e to dep h a s e the following pulses of "exposure". The d u r a -
I
....
I I
I
time of'exposure"I
j
n
1
H
Fig. 1. Block diagram of the device with the forms of the pulses respectively.