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Population transfer on Ne metastable atoms
Volume 53A, number 3
PHYSICS LETTERS
16 June 1975
POPULATION TRANSFER ON Ne METASTABLE ATOMS J. LEVEAU, S. VALIGNAT, F. DEIGAT and A. ERBEIA ERA CNRS no 302, Université Claude Bernard, Laboratoire de Spec~rosco pie et de Luminescence, 43, BId du 11 November 1918, 69621 Villeurbanne, France Received 1 April 1975 We describe an experiment allowing transfer measurement on metastable levels of neon of the perturbation induced by the 6328 A laser light on the upper levels. First results are given.
One of the most important effects induced by a laser beam into an atomic vapour is to produce selective population changes in the atomic levels a and b of the laser transition [1,2]. In steady state conditions, these variations can be written for any levels a (a = a or b) using linear approximation:
2
__________
( 3Pj
~
1~’~\_____
(L~.n)KI’1~NX(p)
-
—
-4
2p
where K is a constant, ~N = Na Nb is the population difference, between the a and b states of the atom, f~ is the decay constant of the a level, X(j.t) is a function which depends on the laser modes and Doppler profile oftheline. We are interested here by the transfer of the perturbation induced by the laser between 3s2 and 2P4 levels on metastable andtransition pseudo-metastable lSkl,2,3,4 levels of neon (fig. 1). In order to detect population changes (~~)1Sk in each I s level, we use an absorption method with an optical beam of I~,intensity. In first approximation (I,~ weak), we can write [31:
1
—
‘4k1
i h— i~1 I
-
: -
II
l~ J—
Fig. 1. Schematic energy level diagrams of Ne. Paschen notation is used.
mator receives simultaneously the ‘F fluorescent light
~,A
1~k11A isk
=
(z~n) lsklIN isk
where 1A = ‘T and L~I~Sk is the absorbed light variation due to laser irradiation. The experimental arrangement is illustrated in fig. 2. We use two parallel cylindrical tubes R and C. Tube R plays the role of a resonance lamp. I~light emitted by R is sinusoidally modulated at f1 frequency. Tube C which contains the gas under investigation is supplied by direct current and is located inside the laser cavity. Its working conditions can be changed without laser oscillation alteration. The laser beam is chopped atf2 frequency which can vary up to several khz. The PM1 photomultiplier tube located behind a monochro—
emitted byand frequency C tube, the ‘T which lightisemitted weaklyby modulated R tube, passing atf2 through C tube, which is then modulated at f1 and frequencies. f1 and f2 components of the photoelectric current of PM1 are cancelled by the mean of another photomultiplier tube (PM2) and a differential amplifier. The ~jA and 1A signals are detected by a synchronous detector locked respectively at f1 and f1 +f2 frequencies. First experiments conducted with pure neon show an absorption variation by is3 level for a pressure p~ = 1 T and a discharge current i~ = 8 mA, by is3 1841 S5 levels if p = 2T, i~= 8 mA and by ls2 level if p~= 2T, i~= 50 mA.
f1 ±f2
243
Volume 53A, number 3
PHYSICS LETTERS
16 June 1975
~
~,,IC
-. —.
~•m sin 21Tf
1t)
j__
Diff.r.ntiaI I
I
ampllfisr
______________
i~Ii~~
______________
~~:::~:j~___1R.cord.r I f1 or ~f1+f 2)
Fig. 2. Experimental set-up.
Relative absorption variations are found to be about l0~ with a detection sensitivity of the measurement system of ~ In pure neon the 3s2 level population increases with the laser power while the 2p4 level population simultaneously decreases. The other 2p as well as 3p states are connected to each ~ by spontaneous emission. Furthermore, inside of group these levels are more or less coupled to each other by collisions. This phenomenon depends on the energy difference between the levels. Most of the time, population of nearly all of these levels varies in phase with the ~ level population [4]. It may be written: ‘
~
—
__L I [‘~5~\
Over our measurement range, we detect population variation in phase with the laser power for the is3 level. This result arises from the fact that the Is3 level is not optically connected to the 2p4. Inversely, is2, 1s4 and is5 level populations vary out of phase with the laser power. This indicates that the perturbation 2p~ transfer is mainly achieved by coupling with the level. In addition to the study of the transfer in neon, this experiment must give some results concerning metastable levels, peculiarly about their decay constants and their population exchange collision coefficients [5].
References
~ 72pj—~1sk’~~J2p 1
13p/-+lsk (~n) +
‘
3~1)
72pj-.lsk and Y3p/-~1skare the 2Pi~~~’1~k and where 1~ktransition probabilities.
244
~1J W.E. Lamb,Jr., Phys. Rev. 134 (1964) A1429. 121 M. Dumont and B. Decomps, J. Phys. 29 (1968) 181. [3] A.C.G. Mitchell and M.W. Zemansky, Resonance radiation and excited atoms (1934). [4] 1528. L.A. Weaver and R.J. Freiberg, J. Appl. Phys. 37 (1966) [5] A.V. Phelps, Phys. Rev. 114 (1959) 1011.
PHYSICS LETTERS
16 June 1975
POPULATION TRANSFER ON Ne METASTABLE ATOMS J. LEVEAU, S. VALIGNAT, F. DEIGAT and A. ERBEIA ERA CNRS no 302, Université Claude Bernard, Laboratoire de Spec~rosco pie et de Luminescence, 43, BId du 11 November 1918, 69621 Villeurbanne, France Received 1 April 1975 We describe an experiment allowing transfer measurement on metastable levels of neon of the perturbation induced by the 6328 A laser light on the upper levels. First results are given.
One of the most important effects induced by a laser beam into an atomic vapour is to produce selective population changes in the atomic levels a and b of the laser transition [1,2]. In steady state conditions, these variations can be written for any levels a (a = a or b) using linear approximation:
2
__________
( 3Pj
~
1~’~\_____
(L~.n)KI’1~NX(p)
-
—
-4
2p
where K is a constant, ~N = Na Nb is the population difference, between the a and b states of the atom, f~ is the decay constant of the a level, X(j.t) is a function which depends on the laser modes and Doppler profile oftheline. We are interested here by the transfer of the perturbation induced by the laser between 3s2 and 2P4 levels on metastable andtransition pseudo-metastable lSkl,2,3,4 levels of neon (fig. 1). In order to detect population changes (~~)1Sk in each I s level, we use an absorption method with an optical beam of I~,intensity. In first approximation (I,~ weak), we can write [31:
1
—
‘4k1
i h— i~1 I
-
: -
II
l~ J—
Fig. 1. Schematic energy level diagrams of Ne. Paschen notation is used.
mator receives simultaneously the ‘F fluorescent light
~,A
1~k11A isk
=
(z~n) lsklIN isk
where 1A = ‘T and L~I~Sk is the absorbed light variation due to laser irradiation. The experimental arrangement is illustrated in fig. 2. We use two parallel cylindrical tubes R and C. Tube R plays the role of a resonance lamp. I~light emitted by R is sinusoidally modulated at f1 frequency. Tube C which contains the gas under investigation is supplied by direct current and is located inside the laser cavity. Its working conditions can be changed without laser oscillation alteration. The laser beam is chopped atf2 frequency which can vary up to several khz. The PM1 photomultiplier tube located behind a monochro—
emitted byand frequency C tube, the ‘T which lightisemitted weaklyby modulated R tube, passing atf2 through C tube, which is then modulated at f1 and frequencies. f1 and f2 components of the photoelectric current of PM1 are cancelled by the mean of another photomultiplier tube (PM2) and a differential amplifier. The ~jA and 1A signals are detected by a synchronous detector locked respectively at f1 and f1 +f2 frequencies. First experiments conducted with pure neon show an absorption variation by is3 level for a pressure p~ = 1 T and a discharge current i~ = 8 mA, by is3 1841 S5 levels if p = 2T, i~= 8 mA and by ls2 level if p~= 2T, i~= 50 mA.
f1 ±f2
243
Volume 53A, number 3
PHYSICS LETTERS
16 June 1975
~
~,,IC
-. —.
~•m sin 21Tf
1t)
j__
Diff.r.ntiaI I
I
ampllfisr
______________
i~Ii~~
______________
~~:::~:j~___1R.cord.r I f1 or ~f1+f 2)
Fig. 2. Experimental set-up.
Relative absorption variations are found to be about l0~ with a detection sensitivity of the measurement system of ~ In pure neon the 3s2 level population increases with the laser power while the 2p4 level population simultaneously decreases. The other 2p as well as 3p states are connected to each ~ by spontaneous emission. Furthermore, inside of group these levels are more or less coupled to each other by collisions. This phenomenon depends on the energy difference between the levels. Most of the time, population of nearly all of these levels varies in phase with the ~ level population [4]. It may be written: ‘
~
—
__L I [‘~5~\
Over our measurement range, we detect population variation in phase with the laser power for the is3 level. This result arises from the fact that the Is3 level is not optically connected to the 2p4. Inversely, is2, 1s4 and is5 level populations vary out of phase with the laser power. This indicates that the perturbation 2p~ transfer is mainly achieved by coupling with the level. In addition to the study of the transfer in neon, this experiment must give some results concerning metastable levels, peculiarly about their decay constants and their population exchange collision coefficients [5].
References
~ 72pj—~1sk’~~J2p 1
13p/-+lsk (~n) +
‘
3~1)
72pj-.lsk and Y3p/-~1skare the 2Pi~~~’1~k and where 1~ktransition probabilities.
244
~1J W.E. Lamb,Jr., Phys. Rev. 134 (1964) A1429. 121 M. Dumont and B. Decomps, J. Phys. 29 (1968) 181. [3] A.C.G. Mitchell and M.W. Zemansky, Resonance radiation and excited atoms (1934). [4] 1528. L.A. Weaver and R.J. Freiberg, J. Appl. Phys. 37 (1966) [5] A.V. Phelps, Phys. Rev. 114 (1959) 1011.