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Magnetic modulation of light beams
288
ABSTRACTS OF CONTRIBUTED PAPERS, SECTION C
electronic and orientational degeneracy removed by the application of the magnetic field. The number of components will be listed for different orientations of the magnetic field and polarization intensities will be described where possible. Examples will be drawn from the Zeeman spectra of calcium fluoride crystals doped with divalent and trivalent rare-earth ions. A spin selection rule m a y cause negative Zeeman results in colour centres even when Kramers degeneracy is present. C6
B. BRIAT, M. BILLARDON and J. BADOZ, published in full, see p. 230.
C7
J. MARGERIE, published in full, see p. 238.
C8
L. VAN GERVEN, published in full, see p. 250.
C9
J . W . M . DEKKER and R. HOEKSTRA, Zeeman-Laboratorium, Amsterdam.
Small isotope shifts in the spectrum o / D y I.
Isotope shifts have been measured between the isotopes 162 and 164 in the spectrum of D y I. The results for five strong lines are summarized in the following table. TABLE I Isotope Shift between 162Dy and X64Dyin 5 Dy arc lines A (A} Isotope Shift (mK) 4045.99 12.0 4- 0.2 4167.99 --20.1 + 0.2 4186.78 --18.3 i 0.2 4194.85 --14.2 4- 0.2 4211.75 --30.3 4- 0.3 The measuring apparatus was a Fabry-P6rot spectrometer (Hyp6ac). The smallness of the shifts required the use of a system of interchangeable liquid nitrogen cooled hollow cathodes. One of the cathodes was charged with isotope sample 162 and a second one with sample 164. Isotope shifts were measured by comparing the line position of one isotope with respect to the other in successive orders of the etalon. Care has been taken t h a t no systematic instrumental shifts were introduced. C10
D. WILLIAMS, Kansas State University, Manhatten, Kansas.
Magnetic Modulation of Light Beams. The development of intense coherent light sources has resulted in renewed interest in the problem of light-beam modulation. The well known enormous enhancement of the F a r a d a y effect at optical frequencies in the vicinity of sharp absorption lines offers the basis of a rather simple method of providing "deep modulation". Although Bohr 1) once proposed the Larmor frequency as an upper modulation limit, the expressions of Kramers 2) and Kuhn 8) for the magnetic rotation associated with electric-dipole 1) Bohr, N., Naturwiss. | ~ (1925) 1115. 2) Kramers, H. A., Proc. Acad. Sci. Amsterdam 33 (1930) 959. 3) Kuhn, W., Danske Videnskab~,nes Selskab (Zfirieh Habilitationsschrift, 1926). Summarized by Mitchell, A. C. G. and Zemansky, M. W., Resonance Radiation and Excited Atoms (Cambridge University Press, London, 1934).
ABSTRACTS OF CONTRIBUTED PAPERS, SECTION C
9~89
transitions do n o t suggest a n y u p p e r f r e q u e n c y limit for modulation. I n recent theoretical work, Shen and B l o e m b e r g e n I) h a v e a t t e m p t e d to include all t y p e s of t r a n sitions. These a u t h o r s o b t a i n e d an expression for t h e d i a m a g n e t i c and p a r a m a g n e t i c c o n t r i b u t i o n s to t h e n e t m a g n e t i c r o t a t i o n ; t h e former has no u p p e r f r e q u e n c y limit b u t t h e l a t t e r is severely limited b y t h e spin-lattice r e l a x a t i o n t i m e of t h e sample. T h e e x p e r i m e n t a l w o r k of S c h m i d t e. a. 2) will be r e - e x a m i n e d in t e r m s of recent t h e o r y ; t h e results for s o d i u m v a p o r indicate t h a t t h e p a r a m a g n e t i c c o n t r i b u t i o n is small e v e n a t low frequencies. P r a c t i c a l u p p e r f r e q u e n c y limitations on F a r a d a y effect m o d u l a t i o n will be discussed. DISCUSSION
G. W. Series (Oxford): H a v e you considered a d d i n g a static longitudinal field ? I w o u l d e x p e c t t h e a m p l i t u d e of m o d u l a t i o n to show resonances, as a function of longit u d i n a l field strength. D. Williams: W e did no e x p e r i m e n t s i n v o l v i n g static biasing fields - b u t t h e y would of course, be of interest. A. Corney (Boulder): I t would be possible to o v e r c o m e t h e difficulty of t h e decrease in i n t e n s i t y of t h e light t r a n s m i t t e d t h r o u g h t h e v a p o u r w h e n resonance r a d i a t i o n is being used if one worked on a laser transition. T h u s one could pass light f r o m a laser oscillator t h r o u g h a n o t h e r laser discharge t u b e which has no end windows. T h e second t u b e can be used for F a r a d a y m o d u l a t i o n w i t h an increase in intensity, r a t h e r t h a n a decrease. CII
J. BLAMONT, Universit6 de Paris.
Results in Geophysics and Astrophysics obtained with Zeeman modulated Vapours used as Spectrometers. s) L a m 6 t h o d e d ' a n a l y s e spectrale qui consiste ~t utiliser la r6sonance o p t i q u e d ' u n e v a p e u r m6tallique d o n t on fait v a r i e r la fr6quence de r6sonance p a r effet Zeeman, est pr6sent6e. D e u x cas particuliers a v e c leurs applications s o n t discut6s. D a n s le p r e m i e r cas, une r6solution r e l a t i v e m e n t faible, de l'ordre de 2 g 3.10 -3 A est o b t e n u e p a r utilisation de la v a p e u r de sodium. Cette m 6 t h o d e a permis la mise en 6vidence et l'6tude s y s t 6 m a t i q u e de l'6mission naturelle du sodium dans la h a u t e a t m o s p h e r e 95 k m d ' a l t i t u d e . Les r6sultats de cette $tude du s o d i u m a t m o s p h 6 r i q u e s o n t pr6sent6s. D a n s le deuxi~me cas, une h a u t e r6solution de l'ordre de 0,5 × 10 -3 A est a t t e i n t e en utilisant un j e t a t o m i q u e . Les r6sultats obtenus a v e c des jets a t o m i q u e s de calcium, de b a r y u m , de s t r o n t i u m sur la forme des raies de F r a u n h o f e r o n t permis de pr6senter u n n o u v e a u module de la p h o t o s p h e r e solaire. DISCUSSION
Th. G. Eck (Cleveland): W h a t are t h e o t h e r techniques of scanning ? J . Blamont: The o t h e r t e c h n i q u e s we are using are:
a) isotope shift: in t h e case of L y m a n alpha, d e u t e r i u m and h y d r o g e n h a v e a reso1) Shen, Y. R., Phys. Rev. 133 (1964) A511. B l o e m b e r g e n , N. and Shen, Y. R., J. Opt. Soc. Am. 54 (1964) 551. 2) S c h m i d t , B. M., W i l l i a m s , J. M. and W i l l i a m s , D., J. Opt. Soc. Am. 54 (1964) 454. 3) Complete paper to be published in J. opt. Soc. Amer.
ABSTRACTS OF CONTRIBUTED PAPERS, SECTION C
electronic and orientational degeneracy removed by the application of the magnetic field. The number of components will be listed for different orientations of the magnetic field and polarization intensities will be described where possible. Examples will be drawn from the Zeeman spectra of calcium fluoride crystals doped with divalent and trivalent rare-earth ions. A spin selection rule m a y cause negative Zeeman results in colour centres even when Kramers degeneracy is present. C6
B. BRIAT, M. BILLARDON and J. BADOZ, published in full, see p. 230.
C7
J. MARGERIE, published in full, see p. 238.
C8
L. VAN GERVEN, published in full, see p. 250.
C9
J . W . M . DEKKER and R. HOEKSTRA, Zeeman-Laboratorium, Amsterdam.
Small isotope shifts in the spectrum o / D y I.
Isotope shifts have been measured between the isotopes 162 and 164 in the spectrum of D y I. The results for five strong lines are summarized in the following table. TABLE I Isotope Shift between 162Dy and X64Dyin 5 Dy arc lines A (A} Isotope Shift (mK) 4045.99 12.0 4- 0.2 4167.99 --20.1 + 0.2 4186.78 --18.3 i 0.2 4194.85 --14.2 4- 0.2 4211.75 --30.3 4- 0.3 The measuring apparatus was a Fabry-P6rot spectrometer (Hyp6ac). The smallness of the shifts required the use of a system of interchangeable liquid nitrogen cooled hollow cathodes. One of the cathodes was charged with isotope sample 162 and a second one with sample 164. Isotope shifts were measured by comparing the line position of one isotope with respect to the other in successive orders of the etalon. Care has been taken t h a t no systematic instrumental shifts were introduced. C10
D. WILLIAMS, Kansas State University, Manhatten, Kansas.
Magnetic Modulation of Light Beams. The development of intense coherent light sources has resulted in renewed interest in the problem of light-beam modulation. The well known enormous enhancement of the F a r a d a y effect at optical frequencies in the vicinity of sharp absorption lines offers the basis of a rather simple method of providing "deep modulation". Although Bohr 1) once proposed the Larmor frequency as an upper modulation limit, the expressions of Kramers 2) and Kuhn 8) for the magnetic rotation associated with electric-dipole 1) Bohr, N., Naturwiss. | ~ (1925) 1115. 2) Kramers, H. A., Proc. Acad. Sci. Amsterdam 33 (1930) 959. 3) Kuhn, W., Danske Videnskab~,nes Selskab (Zfirieh Habilitationsschrift, 1926). Summarized by Mitchell, A. C. G. and Zemansky, M. W., Resonance Radiation and Excited Atoms (Cambridge University Press, London, 1934).
ABSTRACTS OF CONTRIBUTED PAPERS, SECTION C
9~89
transitions do n o t suggest a n y u p p e r f r e q u e n c y limit for modulation. I n recent theoretical work, Shen and B l o e m b e r g e n I) h a v e a t t e m p t e d to include all t y p e s of t r a n sitions. These a u t h o r s o b t a i n e d an expression for t h e d i a m a g n e t i c and p a r a m a g n e t i c c o n t r i b u t i o n s to t h e n e t m a g n e t i c r o t a t i o n ; t h e former has no u p p e r f r e q u e n c y limit b u t t h e l a t t e r is severely limited b y t h e spin-lattice r e l a x a t i o n t i m e of t h e sample. T h e e x p e r i m e n t a l w o r k of S c h m i d t e. a. 2) will be r e - e x a m i n e d in t e r m s of recent t h e o r y ; t h e results for s o d i u m v a p o r indicate t h a t t h e p a r a m a g n e t i c c o n t r i b u t i o n is small e v e n a t low frequencies. P r a c t i c a l u p p e r f r e q u e n c y limitations on F a r a d a y effect m o d u l a t i o n will be discussed. DISCUSSION
G. W. Series (Oxford): H a v e you considered a d d i n g a static longitudinal field ? I w o u l d e x p e c t t h e a m p l i t u d e of m o d u l a t i o n to show resonances, as a function of longit u d i n a l field strength. D. Williams: W e did no e x p e r i m e n t s i n v o l v i n g static biasing fields - b u t t h e y would of course, be of interest. A. Corney (Boulder): I t would be possible to o v e r c o m e t h e difficulty of t h e decrease in i n t e n s i t y of t h e light t r a n s m i t t e d t h r o u g h t h e v a p o u r w h e n resonance r a d i a t i o n is being used if one worked on a laser transition. T h u s one could pass light f r o m a laser oscillator t h r o u g h a n o t h e r laser discharge t u b e which has no end windows. T h e second t u b e can be used for F a r a d a y m o d u l a t i o n w i t h an increase in intensity, r a t h e r t h a n a decrease. CII
J. BLAMONT, Universit6 de Paris.
Results in Geophysics and Astrophysics obtained with Zeeman modulated Vapours used as Spectrometers. s) L a m 6 t h o d e d ' a n a l y s e spectrale qui consiste ~t utiliser la r6sonance o p t i q u e d ' u n e v a p e u r m6tallique d o n t on fait v a r i e r la fr6quence de r6sonance p a r effet Zeeman, est pr6sent6e. D e u x cas particuliers a v e c leurs applications s o n t discut6s. D a n s le p r e m i e r cas, une r6solution r e l a t i v e m e n t faible, de l'ordre de 2 g 3.10 -3 A est o b t e n u e p a r utilisation de la v a p e u r de sodium. Cette m 6 t h o d e a permis la mise en 6vidence et l'6tude s y s t 6 m a t i q u e de l'6mission naturelle du sodium dans la h a u t e a t m o s p h e r e 95 k m d ' a l t i t u d e . Les r6sultats de cette $tude du s o d i u m a t m o s p h 6 r i q u e s o n t pr6sent6s. D a n s le deuxi~me cas, une h a u t e r6solution de l'ordre de 0,5 × 10 -3 A est a t t e i n t e en utilisant un j e t a t o m i q u e . Les r6sultats obtenus a v e c des jets a t o m i q u e s de calcium, de b a r y u m , de s t r o n t i u m sur la forme des raies de F r a u n h o f e r o n t permis de pr6senter u n n o u v e a u module de la p h o t o s p h e r e solaire. DISCUSSION
Th. G. Eck (Cleveland): W h a t are t h e o t h e r techniques of scanning ? J . Blamont: The o t h e r t e c h n i q u e s we are using are:
a) isotope shift: in t h e case of L y m a n alpha, d e u t e r i u m and h y d r o g e n h a v e a reso1) Shen, Y. R., Phys. Rev. 133 (1964) A511. B l o e m b e r g e n , N. and Shen, Y. R., J. Opt. Soc. Am. 54 (1964) 551. 2) S c h m i d t , B. M., W i l l i a m s , J. M. and W i l l i a m s , D., J. Opt. Soc. Am. 54 (1964) 454. 3) Complete paper to be published in J. opt. Soc. Amer.