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Two-photon spectroscopy of ytterbium
Volume 28, number 2
OPTICS COMMUNICATIONS
February 1979
TWO-PHOTON SPECTROSCOPY OF YTTERBIUM M.Y. MIRZA and W.W. DULEY Physics Department, York University, Downsview, Ontario, Canada M3J 1P3
Received 30 October 1978
Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f 14 6sns 1So and 4f 14 6snd 1D2 states are seen in direct two-photon excitation. Hybrid resonances involving 4f 14 6s6p 1p~ and 4f 14 5d6s 3D2 intermediate states lead to transitions to 4 f 14 6sns 1 SO , 4f14 6snp 3P~, 1 and 4f 14 6s nd 1D2 levels.
In 1937 Meggers and Scribner [1 ] reported the first analysis of the spectrum of ytterbium. Their analysis of the spectrum of YbI included assignment of the first few members of the 4f 14 6s 2 1 SO _ 4f14 6sns, 4f 14 6snp and 4f 14 6snd series. This analysis was subsequently extended by Meggers and Corliss [2]. Parr and Elder [3] measured the photoionization spectrum of Yb in the 1 3 0 0 - 1 7 0 0 A region and found that it was dominated by transitions to autoionizing states. The absorption spectrum o f Yb was recorded for wavelengths between 1980 and 2300 A by Camus and Tomkins [4] and the series 4f 14 6s 2 1S 0 ~ 4f 14 6snp 1P~l(6 ~
6snd 1 D2 states. We have also observed sequential twophoton transitions through resonant dissociative molecular states of Yb 2. These hybrid resonances, which are similar to those observed previously in indium [8], lithium [9], cesium [10] and rubidium [11] result in the development of the series 4f 14 6s6p 1P~I ~ 4f 14 6snd 1D2, 4f 14 6s6p 1P~I ~ 4f14 6sns 1 S0 and 4f 14 5d6s 3D 2 ~ 4f 14 6snp 3P~2. Figs. 1 and 2 show spectra obtained from Yb vapor in the region between 3900 and 4550 A. Both direct and hybrid two-photon transitions can be seen in these spectra. Table 1 lists the energies o f states observed in these transitions together with quantum defects calculated with the ionization potential of Camus and Tomkins [4]. These energies are accurate to -+ 0.75 cm - 1 . Where our measured energies overlap with those of Camus and Tomkins [4] good agreement exists between the two sets of data. However we have extended measurements for the energies of these states to n = 21 for 4f 14 6snd 1D2, n = 18 for 4f 14 6sns 1S0 and n = 37 for 4f 14 6snp 3P~2. Quantum defect plots for these levels are shown in figs. 3 - 5 . These plots show evidence for perturbations in the 6snp 3~2,1 levels near n = 18 and in the 6snd 1D 2 level near n = 8. Figs. 1 and 2 show that much of the laser spectrum o f Yb is dominated by transitions through intermediate atomic states (hybrid resonances). It now appears that hybrid resonances occur in the two-photon spectra of most atoms and that through these resonances it is possible to obtain additional information on Rydberg states. In Yb hybrid resonances occur when 179
Volume 28, number 2
4fl'~S6p ~
OPTICS COMMUNICATIONS
4 f ~ s n d /02 9i
--
I01
4f~sns ZSo
4f~6se JSo_ 4 f / 4 6 s n d
14
131
81
--4f~6sns tSo
4450
#1
I
I
I
I
4400
4350
4300
4250
LASER
4200
/41 /51
-- I01
/ol
I
I
131 /41
91
91
4500
12I
121
I1:
/D2
zl
4550
February 1979
//I
/31
/~
4/50
4/00
WAVELENGTH
Fig. 1. Plot o f ionization current resulting from t w o - p h o t o n transitions in y t t e r b i u m for laser wavelengths 4 5 0 0 - 4 1 0 0 A
4[146S6p ~°--4ft~6snd 141 ,51
//I
/51
/81/912012/122~31
%
,4 161 'So /71
- - 4 f 6sns /61 171 /81 4f*~6S e I S ~ - 4 F ~ 6 s n d JDe 121 ,4 /3] 141
/81
/91 201 211
I I 1 11111111III37
I,,
I,~
/51 /61 /71/SVgt
I~
--4f 6sns 'So
131
141
/,51
/6~
171 18I
Io
...4
<3
\
4100
I
4075
4050
4025
I
I
4000 3975 LASER WAVELENGTH
I
I
3950
3925
3900
Fig. 2. Similar plot (as in fig. 1) for laser wavelengths 4 1 0 0 - 3 9 0 0 A. The one p h o t o n transition 4 f 14 6s 2 z So "+ 4f 14 6s6p 1 pO at 3989.1 A is marked b y a vertical arrow.
180
Volume 28, number 2
February 1979
OPTICS COMMUNICATIONS
Table 1 Vacuum energies (cm -1 ) and quantum defects for n 1D2 ' n 1So, and n 3pO,1 levels of Yb. n
1D2
O1D2
7 8 9 10 11 12 13 14 15 16 17 18 19 2O 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
44760.3 46081.8 47420.9 48133.4 48722.8 49045.3 49300.7 49499.9 49653.0 39773.0 49862.6 49941.0 50001.9 50051.8 50094.8
2.60 2.98 2.97 3.10 3.01 3.13 3.19 3.20 3.20 3.18 3.23 3.19 3.19 3.21 3.20
I
This w o r k
•
Others
0
3
0
o Levels
o
•
0
0
0 0 0 0 0 0 0 0 0
Q Q
I 5
I I0
I 15
I 2.0
Fig. 3. Quantum defect plots for n 1D2 levels.
1SO
01 So
45338.0 46892.1 47822.3 48404.8 48882.0 49176.0 49404.9 49582.9 49717.7 49835.3
4.36 4.44 4.53 4.66 4.61 4.69 4.71 4.69 4.68 4.54
3pO, 1
49921.2 49967.4 50021.1 50061.4 50101.8 50137.2 50166.5 50193.2 50217.0 50236.5 50253.5 50267.8 50281.6 50292.6 50303.3 50313.3 50320.7 50328.1 50336.2 50342.4
3.47 3.78 3.83 4.00 4.01 3.99 4.01 3.96 3.97 3.84 3.81 3.83 3.76 3.81 3.77 3.69 3.80 3.82 3.64 3.64
the first laser photon is absorbed by a Yb 2 molecule in its ground (6s 2 1 SO + 6s 2 1 SO) state causing it to make a transition to dissociative molecular states associated with the (6s 2 1 SO + 6s6p 1P~I) or (6s 2 1S0 + 5s6d 3D2) atomic states. These states dissociate to yield Yb atoms in either the 6s6p 1P~I or 5s6d 3D 2 states. The second laser photon is then absorbed by these excited atoms yielding transitions to 1D2 ' 1 SO and 3P~2,1 states. At 0 K hybrid resonances leading to the excitation of 1D2 and 1 SO states would be seen only for laser wavelengths, X < 3989.1 A, the wavelength of the 6s 2 1 SO ~ 6s6p 1P~I transition. At higher temperatures, however, thermal population of dissociative levels of the ground state of Yb 2 permits transitions to be excited for a range of wavelengths that slightly exceeds 3989.1 A, Fig. 1 shows that hy181
Volume 28, number 2
OPTICS COMMUNICATIONS
February 1979
/ SO - L e v e l s o
This work
*
Others
0 0 0 0 •
•
3P•/-
Levels
0
This work
•
Others
0 0 0
0
0
0
000~00
O~
0 0
3 5
I
I
I0
1.5
20
Fig. 4. Quantum defect plot for n 1So levels. The data of Nir [5] is shown in this and fig. 3 for comparison.
brid resonances can be seen at wavelengths of up to 4340 A under the conditions of our experiments. These transitions occur from excited levels of the Yb 2 ground state that are populated thermally at 900 K. The transition probability for direct two-photon transitions is enhanced by the existence of intermediate states of the appropriate parity [12]. Fig. 2 shows that the one photon 4f 14 6s 2 1S 0 ~ 4f 14 6s6p 1P~I transition at 3989.1 A occurs in the range of the 6s 2 1S0 ~ 6sns 1S 0 and 6snd 1D 2 direct two photon transitions. Thus enhancement of these two photon transitions is expected and can be seen particularly for the 1D2 series when n ~< 18. This resonant enhancement compensates in part for the decrease in transition probability that normally attends transitions to high lying Rydberg states. This research was supported by a grant from the National Research Council of Canada.
182
31
I 20
I 25
I 30
O0
I 35
Fig. 5. Quantum defect plot for n 3P°,l levels. The data of Camus and Tomkins [4] is reproduced for comparison.
References [1 ] W.F. Meggers and B.F. Scribner, J. Res. Nat. Bur. Std. 19 (1937) 651. [2] W.F. Meggers and C.H. Corliss, J. Res. Nat. Bur. Std. 70A (1966) 63. [3] A.C. Parr and F.A. Eider, J. Chem. Phys. 49 (1968) 2665. [4] P.O. Camus and F.S. Tomkins, J. de Physique 30 (1969) 545. [5] S. Nir, J. Opt. Soc. Am. 60 (1970) 354. [6] E.F. Worden, R.W. Solarz, J.A. Paisner, K. Rajnok, B.W. Shore and J.G. Conway, Colloques Internationausedu Centre National de la Recherche Scientifique No. 273 (June 1977). [7] P. Camus, A. Debarre and C. Morillon, J. Phys. Bll (1978) L395. [8] M.Y. Mirza and W.W. Duley, Proc. Roy. Soc. (in press). [9] M.Y. Mirza and W.W. Duley, (unpublished). [10] M.Y. Mirza and W.W. Duley, J. Phys. Bll (1978) 1917 and reference cited therein. [11] C.B. Collins, S.M. I~urrey, B.W. Johnson, M.Y. Mirza, M. Chellehmalzadeh, J.A. Anderson, D. Popescu and I. Popescu, Phys. Rev. A14 (1976) 1662. [ 12] P. Lambropoulos, Topics on multiphoton processes in atoms, Advances in Atomic and Molecular Physics, Vol. 12 (Academic Press, N.Y.) p. 87-164.
OPTICS COMMUNICATIONS
February 1979
TWO-PHOTON SPECTROSCOPY OF YTTERBIUM M.Y. MIRZA and W.W. DULEY Physics Department, York University, Downsview, Ontario, Canada M3J 1P3
Received 30 October 1978
Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f 14 6sns 1So and 4f 14 6snd 1D2 states are seen in direct two-photon excitation. Hybrid resonances involving 4f 14 6s6p 1p~ and 4f 14 5d6s 3D2 intermediate states lead to transitions to 4 f 14 6sns 1 SO , 4f14 6snp 3P~, 1 and 4f 14 6s nd 1D2 levels.
In 1937 Meggers and Scribner [1 ] reported the first analysis of the spectrum of ytterbium. Their analysis of the spectrum of YbI included assignment of the first few members of the 4f 14 6s 2 1 SO _ 4f14 6sns, 4f 14 6snp and 4f 14 6snd series. This analysis was subsequently extended by Meggers and Corliss [2]. Parr and Elder [3] measured the photoionization spectrum of Yb in the 1 3 0 0 - 1 7 0 0 A region and found that it was dominated by transitions to autoionizing states. The absorption spectrum o f Yb was recorded for wavelengths between 1980 and 2300 A by Camus and Tomkins [4] and the series 4f 14 6s 2 1S 0 ~ 4f 14 6snp 1P~l(6 ~
6snd 1 D2 states. We have also observed sequential twophoton transitions through resonant dissociative molecular states of Yb 2. These hybrid resonances, which are similar to those observed previously in indium [8], lithium [9], cesium [10] and rubidium [11] result in the development of the series 4f 14 6s6p 1P~I ~ 4f 14 6snd 1D2, 4f 14 6s6p 1P~I ~ 4f14 6sns 1 S0 and 4f 14 5d6s 3D 2 ~ 4f 14 6snp 3P~2. Figs. 1 and 2 show spectra obtained from Yb vapor in the region between 3900 and 4550 A. Both direct and hybrid two-photon transitions can be seen in these spectra. Table 1 lists the energies o f states observed in these transitions together with quantum defects calculated with the ionization potential of Camus and Tomkins [4]. These energies are accurate to -+ 0.75 cm - 1 . Where our measured energies overlap with those of Camus and Tomkins [4] good agreement exists between the two sets of data. However we have extended measurements for the energies of these states to n = 21 for 4f 14 6snd 1D2, n = 18 for 4f 14 6sns 1S0 and n = 37 for 4f 14 6snp 3P~2. Quantum defect plots for these levels are shown in figs. 3 - 5 . These plots show evidence for perturbations in the 6snp 3~2,1 levels near n = 18 and in the 6snd 1D 2 level near n = 8. Figs. 1 and 2 show that much of the laser spectrum o f Yb is dominated by transitions through intermediate atomic states (hybrid resonances). It now appears that hybrid resonances occur in the two-photon spectra of most atoms and that through these resonances it is possible to obtain additional information on Rydberg states. In Yb hybrid resonances occur when 179
Volume 28, number 2
4fl'~S6p ~
OPTICS COMMUNICATIONS
4 f ~ s n d /02 9i
--
I01
4f~sns ZSo
4f~6se JSo_ 4 f / 4 6 s n d
14
131
81
--4f~6sns tSo
4450
#1
I
I
I
I
4400
4350
4300
4250
LASER
4200
/41 /51
-- I01
/ol
I
I
131 /41
91
91
4500
12I
121
I1:
/D2
zl
4550
February 1979
//I
/31
/~
4/50
4/00
WAVELENGTH
Fig. 1. Plot o f ionization current resulting from t w o - p h o t o n transitions in y t t e r b i u m for laser wavelengths 4 5 0 0 - 4 1 0 0 A
4[146S6p ~°--4ft~6snd 141 ,51
//I
/51
/81/912012/122~31
%
,4 161 'So /71
- - 4 f 6sns /61 171 /81 4f*~6S e I S ~ - 4 F ~ 6 s n d JDe 121 ,4 /3] 141
/81
/91 201 211
I I 1 11111111III37
I,,
I,~
/51 /61 /71/SVgt
I~
--4f 6sns 'So
131
141
/,51
/6~
171 18I
Io
...4
<3
\
4100
I
4075
4050
4025
I
I
4000 3975 LASER WAVELENGTH
I
I
3950
3925
3900
Fig. 2. Similar plot (as in fig. 1) for laser wavelengths 4 1 0 0 - 3 9 0 0 A. The one p h o t o n transition 4 f 14 6s 2 z So "+ 4f 14 6s6p 1 pO at 3989.1 A is marked b y a vertical arrow.
180
Volume 28, number 2
February 1979
OPTICS COMMUNICATIONS
Table 1 Vacuum energies (cm -1 ) and quantum defects for n 1D2 ' n 1So, and n 3pO,1 levels of Yb. n
1D2
O1D2
7 8 9 10 11 12 13 14 15 16 17 18 19 2O 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
44760.3 46081.8 47420.9 48133.4 48722.8 49045.3 49300.7 49499.9 49653.0 39773.0 49862.6 49941.0 50001.9 50051.8 50094.8
2.60 2.98 2.97 3.10 3.01 3.13 3.19 3.20 3.20 3.18 3.23 3.19 3.19 3.21 3.20
I
This w o r k
•
Others
0
3
0
o Levels
o
•
0
0
0 0 0 0 0 0 0 0 0
Q Q
I 5
I I0
I 15
I 2.0
Fig. 3. Quantum defect plots for n 1D2 levels.
1SO
01 So
45338.0 46892.1 47822.3 48404.8 48882.0 49176.0 49404.9 49582.9 49717.7 49835.3
4.36 4.44 4.53 4.66 4.61 4.69 4.71 4.69 4.68 4.54
3pO, 1
49921.2 49967.4 50021.1 50061.4 50101.8 50137.2 50166.5 50193.2 50217.0 50236.5 50253.5 50267.8 50281.6 50292.6 50303.3 50313.3 50320.7 50328.1 50336.2 50342.4
3.47 3.78 3.83 4.00 4.01 3.99 4.01 3.96 3.97 3.84 3.81 3.83 3.76 3.81 3.77 3.69 3.80 3.82 3.64 3.64
the first laser photon is absorbed by a Yb 2 molecule in its ground (6s 2 1 SO + 6s 2 1 SO) state causing it to make a transition to dissociative molecular states associated with the (6s 2 1 SO + 6s6p 1P~I) or (6s 2 1S0 + 5s6d 3D2) atomic states. These states dissociate to yield Yb atoms in either the 6s6p 1P~I or 5s6d 3D 2 states. The second laser photon is then absorbed by these excited atoms yielding transitions to 1D2 ' 1 SO and 3P~2,1 states. At 0 K hybrid resonances leading to the excitation of 1D2 and 1 SO states would be seen only for laser wavelengths, X < 3989.1 A, the wavelength of the 6s 2 1 SO ~ 6s6p 1P~I transition. At higher temperatures, however, thermal population of dissociative levels of the ground state of Yb 2 permits transitions to be excited for a range of wavelengths that slightly exceeds 3989.1 A, Fig. 1 shows that hy181
Volume 28, number 2
OPTICS COMMUNICATIONS
February 1979
/ SO - L e v e l s o
This work
*
Others
0 0 0 0 •
•
3P•/-
Levels
0
This work
•
Others
0 0 0
0
0
0
000~00
O~
0 0
3 5
I
I
I0
1.5
20
Fig. 4. Quantum defect plot for n 1So levels. The data of Nir [5] is shown in this and fig. 3 for comparison.
brid resonances can be seen at wavelengths of up to 4340 A under the conditions of our experiments. These transitions occur from excited levels of the Yb 2 ground state that are populated thermally at 900 K. The transition probability for direct two-photon transitions is enhanced by the existence of intermediate states of the appropriate parity [12]. Fig. 2 shows that the one photon 4f 14 6s 2 1S 0 ~ 4f 14 6s6p 1P~I transition at 3989.1 A occurs in the range of the 6s 2 1S0 ~ 6sns 1S 0 and 6snd 1D 2 direct two photon transitions. Thus enhancement of these two photon transitions is expected and can be seen particularly for the 1D2 series when n ~< 18. This resonant enhancement compensates in part for the decrease in transition probability that normally attends transitions to high lying Rydberg states. This research was supported by a grant from the National Research Council of Canada.
182
31
I 20
I 25
I 30
O0
I 35
Fig. 5. Quantum defect plot for n 3P°,l levels. The data of Camus and Tomkins [4] is reproduced for comparison.
References [1 ] W.F. Meggers and B.F. Scribner, J. Res. Nat. Bur. Std. 19 (1937) 651. [2] W.F. Meggers and C.H. Corliss, J. Res. Nat. Bur. Std. 70A (1966) 63. [3] A.C. Parr and F.A. Eider, J. Chem. Phys. 49 (1968) 2665. [4] P.O. Camus and F.S. Tomkins, J. de Physique 30 (1969) 545. [5] S. Nir, J. Opt. Soc. Am. 60 (1970) 354. [6] E.F. Worden, R.W. Solarz, J.A. Paisner, K. Rajnok, B.W. Shore and J.G. Conway, Colloques Internationausedu Centre National de la Recherche Scientifique No. 273 (June 1977). [7] P. Camus, A. Debarre and C. Morillon, J. Phys. Bll (1978) L395. [8] M.Y. Mirza and W.W. Duley, Proc. Roy. Soc. (in press). [9] M.Y. Mirza and W.W. Duley, (unpublished). [10] M.Y. Mirza and W.W. Duley, J. Phys. Bll (1978) 1917 and reference cited therein. [11] C.B. Collins, S.M. I~urrey, B.W. Johnson, M.Y. Mirza, M. Chellehmalzadeh, J.A. Anderson, D. Popescu and I. Popescu, Phys. Rev. A14 (1976) 1662. [ 12] P. Lambropoulos, Topics on multiphoton processes in atoms, Advances in Atomic and Molecular Physics, Vol. 12 (Academic Press, N.Y.) p. 87-164.