EXPERIMENTAL
DETERMINATION
CHARACTERISTICS SEMITRANSPARENT N.
A.
Rubtsov
OF
THE
OF
EMISSION
THE OF
DISPERSE
MEDIA
and
Emel'yanov
A.
A.
SPECTRAL
UDC 535.58
The study of the s p e c t r a l c h a r a c t e r i s t i c s of s e m i t r a n s p a r e n t d i s p e r s e media is needed for the development of optical communications and optical methods of t e m p e r a t u r e control, as well as for c a r r y i n g out t h e r m a l calculations. In the p r e s e n t r e p o r t we shall propose a high-power device which makes it possible to m e a s u r e diffuse reflection and t r a n s m i s s i o n coefficients, as well as the black-body e m i s s i o n of s c a t t e r i n g media in the lr/3 - 21r/3 range of solid angles. Unlike the p r e v i o u s l y employed r e f r a c t o m e t r i c m e a s u r e m e n t of the s p e c t r a l c h a r a c t e r i s t i c s of solids [1], in the p r o p o s e d optical device substantial simplification of the desigu and a reduction of the o v e r a l l dimensions have been achieved thanks to the use of c o l l i m a t o r s made in the f o r m of paired p a r a bolic m i r r o r s with a central opening. An i m p o r t a n t advantage of the parabolic m i r r o r s employed is the absence of c h r o m a t i c a b e r r a t i o n s . The s p h e r i c a l a b e r r a t i o n s and a s t i g m a t i s m inherent in individual m i r r o r s a r e compensated here to a c e r tain extent, since the a b e r r a t i o n s have opposite signs on the different m i r r o r s . The existing a b e r r a t i o n s a r e displayed weakly in the m e a s u r e m e n t s , since the entrance windows of the light guides have a s m a l l d i a m e t e r (~1 mm). The possibility thus a r i s e s to r e c o r d the e m i s s i o n f r o m points located in d i r e c t proximity to the optical axis, where there a r e p r a c t i c a l l y no sPherical a b e r r a t i o n s . The r e f l e c t o r s have the following c h a r a c t e r i s t i c s : external d i a m e t e r , 200 m m ; d i a m e t e r of the c e n t r a l a p e r t u r e , 40 m m ; f o c a l length, 75 mm. The reflecting l a y e r has been applied to the working s u r f a c e , and the m i r r o r s were counted in p a i r s in one holder. Such an optical shell has a focus located at a distance of 10 m m f r o m the section and a detectable solid angle of v/60-27r/3. The optical apparatus is r e p r e s e n t e d in Fig. 1. Radiation f r o m a standard s o u r c e can enter at m i r r o r I/I, avoiding V and VI, and at m i r r o r I, avoiding all the other c o l l i m a t o r s . This introduces an additional e r r o r into the m e a s u r e m e n t s . F o r this r e a s o n , the c e n t r a l a p e r t u r e s were i n c r e a s e d , and ring d i a p h r a g m s were set up along the path of the radiation. The lower limit of the solid angle has thereby been i n c r e a s e d to ~r/3. The optical apparatus selected has a large a p e r t u r e r a t i o of ~1 : 0.5. Only m o d e r n s u p e r h i g h - p o w e r objectives (1 : 0.65) have such c h a r a c t e r i s t i c s . As shown in Fig. 1, the filament of an SI-10-300 t e m p e r a t u r e lamp is p r o j e c t e d with the aid of t w o c o l l i m a t o r s a r r a n g e d in a row onto object 12, which is located at the focus of the third c o l l i m a t o r . P a r t of the b e a m f r o m the s t a n d a r d s o u r c e p a s s e s through the medium under investigation and, after s u c c e s s i v e reflections f r o m m i r r o r s I and II, r e a c h e s the window of light guide $3, which is placed at focus F 1. The r e s t of the b e a m is s c a t t e r e d in the medium and, a f t e r being reflected f r o m m i r r o r s III and IV, r e a c h e s the window of light guide $1, which is placed at focus F 3. Light guide S2, whose entrance window is placed at focus F3, s e r v e s as a pickup for the incident beam. Light guides S1 and Sz are mounted at focus F 3 in such a m a n n e r that the s c a t t e r e d radiation f r o m the medium is supplied to S1, and the e m i s sion f r o m the s t a n d a r d is supplied to S2. T r a n s l a t e d f r o m Zhurnal Prikladuoi Spektroskopii, Vol. 23, No. 2, pp. 263-267, August, 1975. Original a r t i c l e submitted D e c e m b e r 11, 1973; r e v i s i o n submitted D e c e m b e r 24, 1974. 9 Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o f the publisher. A copy o f this article is available from the publisher for $15.00.
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Fig. 1. Schematic r e p r e s e n t a t i o n of the a p p a r a t u s f o r m e a s u r i n g the s p e c t r a l c h a r a c t e r i s t i c s of s e m i t r a n s p a r e n t d i s p e r s e m e d i a : 1) Motor; 2) m o d u l a t o r ; 3) l a s e r ; 4) DM1R-4 m o n o c h r o m a t o r ; 5, !0) p h o t o m u l t i p l i e r s ; 6, 9) VS-22 high-voltage s o u r c e s ; 7, 11) c u r r e n t a m p l i f i e r s ; 8) loop oscillograph; 12) m e d i u m under investigation; 13) SI-10-300 s t a n d a r d l a m p ; S1-$4) f i b e r light guides; I-VI) p a r a b o l i c mirrors.
The exit ends of light guides S1, 82, and S 3 a r e mounted in a s p e c i a l device which is fixed d i r e c t l y opposite the entrance slit of m o n o c h r o m a t o r 4. This device contains m o d u l a t o r 2, which s u c c e s s i v e l y opens the exit windows of the light guides in front of the e n t r a n c e slit. Modulator 2 is s e t in motion by m o t o r 1. P h o t o m u l t i p l i e r s 5 and 10 s e r v e as radiation d e t e c t o r s . An FEU-27 photomultiplier is used in investigations of the r a d i a t i o n c h a r a c t e r i s t i c s in the n e a r visible region of the s p e c t r u m , and an FEU-83 p h o t o m u l t i p l i e r is used in the red region. The e l e c t r i c a l signal f r o m the p h o t o m u l t i p l t e r s is s u p plied to c u r r e n t a m p l i f i e r s 7 and 11. The signal is r e c o r d e d on loop o s c i l l o g r a p h 8. The constancy of the concentration of the p a r t i c l e s in the d i s p e r s e m e d i u m is m o n i t o r e d a c c o r d i n g to the a b s o r p t i o n of the e m i s s i o n f r o m l a s e r 3. The l a s e r e m i s s i o n that has p a s s e d through the m e d i u m under investigation r e a c h e s pickup S4 and is r e c o r d e d on the loop o s c i l l o g r a p h along with the signals c h a r a c Fig. 2. Typical o s e i l l o g r a m of the t e r i z i n g the optical coefficients of the m e d i u m . F i g u r e 2 p r e measurements. s e n t s an o s c i t l o g r a m of the amplitudes of the signals of the incident radiation (E p ~), t h a t p a s s e d through the m e d i u m (E p ~), and that s c a t t e r e d by the m e d i u m (E p ~). The f i r s t period of the' o'scillogram was made in the a b s e n c e ' 0 f " the m e d i u m at focus F 2. The o s c i l l o ~ r a m c l e a r i n g shows the changes in the amplitudes E p, X and ErP' X" The r a d i a t i o n components r e f l e c t e d in the d i r e c t i o n of the incident b e a m and r e c o r d e d along m e a s u r e m e n t channel S1 a r e equal to Er, z = rxkak4E * ,~.
(1)
EP,~ = rxk3k4kslE*,x,
(2)
and
w h e r e k 3, k 4, and ks1 a r e the attenuation coefficients, and E . , X is the density of the radiation incident to the object. The diffuse r e f l e c t i o n coefficient can be found f r o m the r a t e between the fluxes r e c o r d e d along channels S1 and S2 f r o m the e x p r e s s i o n ESl r~ = K~. ES,,'~~ ,
(3)
w h e r e the i n s t r u m e n t a l constant K X = ksl/k~k]ks1 is d e t e r m i n e d e x p e r i m e n t a l l y a c c o r d i n g to a s a m p l e with a known s p e c t r a l r e f l e c t i o n coefficient. This s a m p l e is a m a g n e s i u m oxide film [2]. The s p e c t r a l t r a n s m i s s i o n coefficient T x is d e t e r m i n e d f r o m the r e l a t i o n
Es:~ T~ ~ -
8s E~,,~
(4). '
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Fig. 3. Spectralcharacteristics of an organic glass. Our data (1) and the data from [3] (2).
O
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Fig. 4. S p e c t r a l c h a r a c t e r i s t i c s of the e m i s s i o n f r o m A1203.
.q~ S, w h e r e E~:~ and E~.~, ~ a r e the r a d i a n t fluxes r e c o r d e d along m e a s u r e m e n t channel S 3 in the p r e s e n c e and a b s e n c e of the d i s p e r s e m e d i u m . The s p e c t r a l a b s o r p t i o n (extinction) coefficient can be found f r o m the balance r e l a t i o n s h i p a~ = 1 - - r~ - - ~x-
(5)
It should be noted that in the g e n e r a l c a s e the b e a m that has p a s s e d through the d i s p e r s e m e d i u m c o n s i s t s of a b e a m s c a t t e r e d into a h e m i s p h e r i c front and a b e a m that p a s s e d s t r a i g h t through. Because of the limited solid angle, p a r t of the s c a t t e r e d b e a m is not r e c o r d e d . T h e r e f o r e , the diffusion absorption coefficients found f r o m Eq. (5) a r e o v e r e s t i m a t e d to a g r e a t e r d e g r e e , the l e s s the s c a t t e r i n g indicatrix of the object under investigation is s t r e t c h e d . T h e r e f o r e , the extinction coefficients a r e d e t e r m i n e d m o r e a c c u r a t e l y f r o m the r a t i o between the b l a c k - b o d y radiant fluxes detected along channet S 3 f r o m the object and the l a m p in the a b s e n c e of the object, which equals
E~
I
E ' (~------~= w h e r e B~ T ~b) and B~ spectively.
k3k,ksk 6
a~
T~,b)B~ T~ b) ~zI (~, Tip) 130 (~,, Tip) ,
(6)
TZp) a r e P l a n c k ' s functions at the t e m p e r a t u r e of the object and the lamp, r e -
B e c a u s e of the high a p e r t u r e ratio, the p r o p o s e d optical a p p a r a t u s is effective in the case of an investigation of weakly s c a t t e r i n g s e m i t r a n s p a r e n t m a t e r i a l s . The p o s s i b i l i t i e s of the device a r e d e m o n s t r a t e d in Figs. 3 and 4. F i g u r e 3 p r e s e n t s the result~ of the m e a s u r e m e n t s of the s p e c t r a l c h a r a c t e r i s t i c s of the e m i s s i o n of an organic g l a s s 10 m m thick at 20~ with a r e l a t i v e s y s t e m a t i c e r r o r of • The figure a l s o p r e s e n t s the data f r o m [3] f o r c o m p a r i s o n . The figure indicates that t h e r e is s a t i s f a c t o r y qualitative a g r e e m e n t between the t r a n s m i s s i o n c u r v e s . The quantitative difference is a p p a r e n t l y due to the fact that the data in [3] r e f e r to n o r m a l radiation. Diff e r e n c e s in the quality of the t r e a t m e n t of the s u r f a c e s of the m a t e r i a l s used and in their s t r u c t u r a l f e a t u r e s due to a d i f f e r e n c e in the m a n u f a c t u r i n g p r o c e s s have not been r u l e d out. F i g u r e 4 p r e s e n t s the r e s u l t s of m e a s u r e m e n t s of the s p e c t r a l e m i s s i o n coefficients f o r A1203 at 20~ The c r o s s section of the d i s p e r s e flux is 3 • 8 m m , the flow r a t e of the p a r t i c l e s is 30 • 3 m g / s e c , and the d i a m e t e r of the p a r t i c l e s r a n g e s f r o m 50 to 90 ~. According to Fig. 4, the t r a n s m i s s i o n c o e f f i cient ~- r e m a i n s p r a c t i c a l l y unchanged in the r a n g e of wavelengths investigated. LITERATURE
CITED
1.
S. S. Kutateladze, N. A. Rubtsov, and G. V. Myakin, Geliotekhnika, No. 3, 18 (1969).
2. 3.
R. G. Wilson and C. R. Spitzer, Raketn. Tekhn. K o s m o n a v t . , 6, 59 (1968).
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R e f e r e n c e Book on Illumination E n g i n e e r i n g [in Russian], Izd. Akad. Nauk SSSR, Moscow (1956).
