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Double γ-and optical resonance
Volume 43A, number 2
PHYSICS LErrERS
26 February 1973
DOUBLE ~y-AND OPTICAL RESONANCE VS. LETOKHOV Institute ofSpectroscopy, Academy of Sciences USSR, Podolskii Rayon, Ak.adomgorodok, USSR
Received 18 Ocotber 1972 The appearance of narrow resonance within the Doppler-broadened absorption line of nuclear transition as a result of the absorption saturation of the atom electron transition and subsequent photoionization of the excited atoms by laser radiations is predicted. There are known two types of narrow resonances in the absorption and emission spectra of substance: 1) absorption and emission resonance of 7-quanta without recoil at nuclear transition in a condensed phase; 2) resonances in gas at electron (vibrational) transitions in the optical range induced by the laser coherent wave. In both cases, in fact, is absent Doppler-broadenmg and the recoil effect which results in extremely narrow resonances (Av/v reaches 10—11 10—15 for nuclear resonances [11and 1 O~ 1010 for optical resonances [2]). In the present letter is considered a possibility of connection 7-and optical resonances, their nature and frequency range being cornpletely different. The possibility to use this effect in experiment is discussed following the example of the —
—
precise measurement of the nucleus recoilgas energy. Let us look upon low pressure atomic satisfying two conditions: 1) at one of the 1ko~nucleus transition the Mossbauer effect is possible under its placing in the condensed medium; 2) at one of the electron transitions from the ground state hoo the radiative and collisional width is much smaller than the Doppler one, i.e. the transition being effected by the coherent light wave, one can obtain the resonance with r0 width much smaller of the Doppler one. For the atom with u velocity absorption frequencies at nuclear and electronic transitions are: 0 ~ (I) 7 .F~ 7 +k 7 v; (0ei~~O+~0V where is the frequency shift due to the nucleus recoil effect; the recoil effect at the electronic transition is neglected as it is toobeam small.of 7-quanta from the Let the collimated
Mössbauer source of radiation on the same nuclei being passed through gas. If the Doppler width of the nuclear transition is &~~ ~ 47 then ~ -quanta are absorbed in gas, and the nuc1leus atoms in the l~spectral interval are being excited, their velocity compensates the recoil effect induced frequency shift: ku—si. 7
(2)
7
Let the coherent light wave from the laser with c~ frequency being tuned within the Doppler width of the electronic transition passes through gas collinearly with 7-beam. The laser beam interacts with the same atoms as 7-beam does, if its frequency coincides with ~ frequency: wo hO.) 7 ~ =~ 1—-——2 (3) 7 2M’c where M is the atom mass. The optical resonance width equals the homogeneous width of f’ 0 transition. The electronic and nuclear transition double resonance of the moving atoms can be detecte4 with the following method. Let the coherent light wave saturate the absorption at the electronic transition, i.e. it cxcites nearby a half of atoms the velocity of which satisfles the condition: j....
,
k0v = ~~las (00 (4) However, it does not influence at all the number transition. This situation can be changed, if in this way or another one makes “an emergence” of excited atoms with velocity (4) from the 7-beam cross-section. The photoionization of excited atoms with an extra laser beam can be just this method. extra beam intensity 6exc At andthe ~ph are the excitation = (~excThpii) ~satthe ( excited atom photoionization cross-section and —
179
Volume 43A, number 2
PHYSICS LETTERS
f7?ô3s~aucrtine
26 February 1973
quency of the coherent wave exciting atoms, then at a lack of atoms arises absorbing 7-radiation from the Mössbauer source (fig. ib). Due to the small absorption coefficient of ~ -radiation in gas it is more convenient, probably, to measure 7-fluorescence tion. minimum arising simultaneously with that of absorp-
KC~d•~ &~Q5&O
~~las=
.i?oppter-poaal’i,ed nuclear
The measurement of the laser frequency detuning ~‘~asinducing resonance under the ~ -quantum absorption or scattering related to the w0 Doppler line centre according to (3) yields automatically the ratio of a~sorplLonof mossoue,emissLon in ~as
S.
________
__________________________
~r
—
______________________________________ las Fig. 1. Doppler-broadened nuclear absorption line with laser-
induced frequency-tunable narrow “hole” (a) and absorption of Mossbauer radiation in gas as funcion of laser frequency (b) (solid line corresponds to the parallel 7-and optical beams, dotted line — antiparallel beams).
cross-section, respectively, ~sat is the power inducing the electronic transition saturation) the photoionization probability of the atom excited for its lifetime is of the order of unit. The ions generated in low pressure gas (1 ~—2torr) are likely to be taken away from the region of 7-and laser beams with a small direct electric field. It results in the ii nucleus velocity pro. jection distribution onto k0 direction that will have the minimum for k7u = COo velocities. It Will lead, in its turn, to’ the simultaneous hole generation in the absorption Doppler lines at electronict~~Ias andfrefluclear transitions (fig. la). If now one scans —
180
7-quantum that of rest energy for atom. In experimentsenergy on the to measurement of the frequency interval between narrow resonances a relative accuracy of 10—10 10—11 is quite real which corresponds to the measurement accuracy for iIw7 /2Mc2 ratio being of 10~—lO—~ atlIw 7 = 100 keY andM= 50 at. unit. Notice that the method described enables us to fulfill 7 -spectroscopy within the neighbouring of Mössbauer transition [‘0/o.,0= 10~ 10—8
is completely impossible to carry out with the existing methods. This method resolution is equal to
(I’71W7 + Fo/o), where r’0 and f’7 -homogeneous
spectral width of optical and nuclear transitions, i.e. it is determined in practice with the relative width of narrow optical, resonances.
References [1] V.S. Shpinel. Gamm-ray resonance in crystals. (Izd. Moscow,Proc. 1969). [2] Nauka, V.S. Letokhov. Esfalian Symp. on Fundamental and applied iaser physics, eds. M.S. Feld, N.A. Kurnit and (John Wiley and Sons, New York, 1972). [3] A.C. Melissinos and S.P. Davis, Phys. Rev. 115 (1959) 130.
PHYSICS LErrERS
26 February 1973
DOUBLE ~y-AND OPTICAL RESONANCE VS. LETOKHOV Institute ofSpectroscopy, Academy of Sciences USSR, Podolskii Rayon, Ak.adomgorodok, USSR
Received 18 Ocotber 1972 The appearance of narrow resonance within the Doppler-broadened absorption line of nuclear transition as a result of the absorption saturation of the atom electron transition and subsequent photoionization of the excited atoms by laser radiations is predicted. There are known two types of narrow resonances in the absorption and emission spectra of substance: 1) absorption and emission resonance of 7-quanta without recoil at nuclear transition in a condensed phase; 2) resonances in gas at electron (vibrational) transitions in the optical range induced by the laser coherent wave. In both cases, in fact, is absent Doppler-broadenmg and the recoil effect which results in extremely narrow resonances (Av/v reaches 10—11 10—15 for nuclear resonances [11and 1 O~ 1010 for optical resonances [2]). In the present letter is considered a possibility of connection 7-and optical resonances, their nature and frequency range being cornpletely different. The possibility to use this effect in experiment is discussed following the example of the —
—
precise measurement of the nucleus recoilgas energy. Let us look upon low pressure atomic satisfying two conditions: 1) at one of the 1ko~nucleus transition the Mossbauer effect is possible under its placing in the condensed medium; 2) at one of the electron transitions from the ground state hoo the radiative and collisional width is much smaller than the Doppler one, i.e. the transition being effected by the coherent light wave, one can obtain the resonance with r0 width much smaller of the Doppler one. For the atom with u velocity absorption frequencies at nuclear and electronic transitions are: 0 ~ (I) 7 .F~ 7 +k 7 v; (0ei~~O+~0V where is the frequency shift due to the nucleus recoil effect; the recoil effect at the electronic transition is neglected as it is toobeam small.of 7-quanta from the Let the collimated
Mössbauer source of radiation on the same nuclei being passed through gas. If the Doppler width of the nuclear transition is &~~ ~ 47 then ~ -quanta are absorbed in gas, and the nuc1leus atoms in the l~spectral interval are being excited, their velocity compensates the recoil effect induced frequency shift: ku—si. 7
(2)
7
Let the coherent light wave from the laser with c~ frequency being tuned within the Doppler width of the electronic transition passes through gas collinearly with 7-beam. The laser beam interacts with the same atoms as 7-beam does, if its frequency coincides with ~ frequency: wo hO.) 7 ~ =~ 1—-——2 (3) 7 2M’c where M is the atom mass. The optical resonance width equals the homogeneous width of f’ 0 transition. The electronic and nuclear transition double resonance of the moving atoms can be detecte4 with the following method. Let the coherent light wave saturate the absorption at the electronic transition, i.e. it cxcites nearby a half of atoms the velocity of which satisfles the condition: j....
,
k0v = ~~las (00 (4) However, it does not influence at all the number transition. This situation can be changed, if in this way or another one makes “an emergence” of excited atoms with velocity (4) from the 7-beam cross-section. The photoionization of excited atoms with an extra laser beam can be just this method. extra beam intensity 6exc At andthe ~ph are the excitation = (~excThpii) ~satthe ( excited atom photoionization cross-section and —
179
Volume 43A, number 2
PHYSICS LETTERS
f7?ô3s~aucrtine
26 February 1973
quency of the coherent wave exciting atoms, then at a lack of atoms arises absorbing 7-radiation from the Mössbauer source (fig. ib). Due to the small absorption coefficient of ~ -radiation in gas it is more convenient, probably, to measure 7-fluorescence tion. minimum arising simultaneously with that of absorp-
KC~d•~ &~Q5&O
~~las=
.i?oppter-poaal’i,ed nuclear
The measurement of the laser frequency detuning ~‘~asinducing resonance under the ~ -quantum absorption or scattering related to the w0 Doppler line centre according to (3) yields automatically the ratio of a~sorplLonof mossoue,emissLon in ~as
S.
________
__________________________
~r
—
______________________________________ las Fig. 1. Doppler-broadened nuclear absorption line with laser-
induced frequency-tunable narrow “hole” (a) and absorption of Mossbauer radiation in gas as funcion of laser frequency (b) (solid line corresponds to the parallel 7-and optical beams, dotted line — antiparallel beams).
cross-section, respectively, ~sat is the power inducing the electronic transition saturation) the photoionization probability of the atom excited for its lifetime is of the order of unit. The ions generated in low pressure gas (1 ~—2torr) are likely to be taken away from the region of 7-and laser beams with a small direct electric field. It results in the ii nucleus velocity pro. jection distribution onto k0 direction that will have the minimum for k7u = COo velocities. It Will lead, in its turn, to’ the simultaneous hole generation in the absorption Doppler lines at electronict~~Ias andfrefluclear transitions (fig. la). If now one scans —
180
7-quantum that of rest energy for atom. In experimentsenergy on the to measurement of the frequency interval between narrow resonances a relative accuracy of 10—10 10—11 is quite real which corresponds to the measurement accuracy for iIw7 /2Mc2 ratio being of 10~—lO—~ atlIw 7 = 100 keY andM= 50 at. unit. Notice that the method described enables us to fulfill 7 -spectroscopy within the neighbouring of Mössbauer transition [‘0/o.,0= 10~ 10—8
is completely impossible to carry out with the existing methods. This method resolution is equal to
(I’71W7 + Fo/o), where r’0 and f’7 -homogeneous
spectral width of optical and nuclear transitions, i.e. it is determined in practice with the relative width of narrow optical, resonances.
References [1] V.S. Shpinel. Gamm-ray resonance in crystals. (Izd. Moscow,Proc. 1969). [2] Nauka, V.S. Letokhov. Esfalian Symp. on Fundamental and applied iaser physics, eds. M.S. Feld, N.A. Kurnit and (John Wiley and Sons, New York, 1972). [3] A.C. Melissinos and S.P. Davis, Phys. Rev. 115 (1959) 130.