- Email: [email protected]
Collinear laser spectroscopy at ionic beams of argon and chlorine
Volume 31, number 3
OPTICS COMMUNICATIONS
December 1979
COLLINEAR LASER SPECTROSCOPY AT IONIC BEAMS OF ARGON AND CHLORINE A. EICHHORN, M. ELBEL and W. KAMKE Fachbereieh Physik tier UniversitatMarburg, D-3550 Marburg/Lahn, Fed. Rep. Germany and J.C. AMARI~ Departamento de Fi'sica Fundamental, Universidad de Zaragoza, Zaragoza-6, Spain Received 10 September 1979
Metastable ions of argon and chlorine were accelerated to form a beam which was led antiparallel to a dye-laser beam. When the laser beam was tuned to transitions from the metastables to higher states and the accelerating voltage was set to compensate for the remaining shift, fluorescence from the ions could be detected. Scanning the voltage excitation spectra of the ions could be obtained which allowed to determine the isotope shift of the lines the laser excited.
Since its first proposal [1] the dynamic reduction o f the Doppler width in fast beam collinear laser spectroscopy was verified at neutral alkalis [2] metastable ions [ 3 - 6 ] and molecules [7,8]. The choice of suitable ionic metastables is limited. It appears that the low energetic metastables of the earth alkalis and lanthanides are superior to the others concerning yield and narrow line width. This is due to their production in thermionic sources whose ionic temperatures are known to be low ( < 1 eV). Metastable ions of gases, howeverl have to be produced in discharges where the local variation of the potential at which the ions are born, contributes considerably to their velocity distribution and hence to the linewidth which can be obtained. Spectroscopic interest and the prospect to have a strong ionic beam pumped optically in flight for application with heavy ion accelerators led us to try chlorine and argon metastable ions as new examples. The ions were formed in an ionic source of the Penning type. A cylindrical anode was closed at both ends by flat metal sheets on cathode potential. One of the sheets which was made of tantalum was indirectly heated by thermal radiation and electron bombard306
ment so that an electron current of > 100 m A could be drawn from it. Argon or vapour o f carbon tetrachloride was admitted through a needle valve to the interior of the electrodes. An axial magnetic field of 100 Oe was applied. An anode voltage of 90 V and a discharge current of 300 mA yielded the maximum production of metastables ions. An ionic current of up to 10 - 5 A was drawn through an axial bore in the other cathode sheet. As the cathode was on ground potential the ions had to be accelerated into a chamber at high negative potential ( - 1 . . . - 3 keV). Into this chamber a line of post accelerating chambers was inserted. The ionic beam could be viewed by a multiplier through lateral holes in the chambers which were covered by thin wire mesh. Metastable argon ions in the state 3p 4 1D 3d 2G9/2 were excited b y laser light at X = 6117 A to the 3p4 1D 4p 2F7/2 state which by decaying to the 3p4 1D 4s 2D5/2 state yielded fluorescent quanta at X = 4611 )~ detected by the multiplier. Analogously, chlorine ions were excited from the metastable state 3p 3 4S 3d 5D 4 to 3p 3 4S 4p "SP3 at )t = 5423.25 )I, whence they decayed to 3p 3 4S 4s 5S 2 emitting light at X = 4795 )k which served for monitoring the excitation.
Volume 31, number 2
OPTICS COMMUNICATIONS
December 1979
l to v a c u u m pump Pe2nsllrce
i ~eCc~ I,ergJ~°n//
~
cl:cl:cX~SJmVe eI?r° t i°n
\ magneticfield / / <
i~'~O V){//4 k
V
,
~
/
F, ~ K ~ _ J .. ~-]l A~.,oov}J~lll II II II I ~/-,L, ,~
<
gas inlet F K A Z
7o°?iJ°ieam
/
window
• i/
_ _<:1. . . .
la~e~b~om
filter photomultiplier
filament cathode anode extractionelectrode Fig. 1. Experimental disposition.
The laser beam was sent antiparallel to the ionic beam. Its wave length was locked to a suitable iodine line whose wave lengths are known to great accuracy [9]. The absorption spectrum of the ions was scanned by sweeping the accelerating voltage. An example of the spectra obtained is given in fig. 2. The sensitivity was good enough to obtain clear spectra from 36Ar whose abundance in the used natural argon is only 0.3 percent. As a result, isotope shifts AVIS of argon and chlorine were obtained. We found
35C1
I
APIs(Ar ) = u(40Ar) - p(36Ar) = - 4 . 2 4 -+ 0.06 GHz APls(C1) = v(37C1) - u(35C1) = - 2 . 1 0 -+ 0.06 GHz. Both values are large and negative. They agree when reduced to equal difference of the atomic mass. They are apparently due to a strong specific mass effect to which the 3d electron gives rise by its momentum correlation with the inner p-shells [10]. No hyperfine splitting of the lines was observed the half width of the lines being 400 MHz. Apparently the hypeffine coupling of the 3p 3 shell which is coupled to a 4S state yields hyperfine splittings smaller than this figure. Thanks are due to Dr. D. Fick, Marburg, for his continuous interest. We acknowledge valuable help by Dr. He. Wagner, Marburg, in the construction and maintenance of the ionic source. Material support by the Deutsche Forschungsgemeinschaft is also acknowledged.
-2000V
I
-1900V
I
-1800V
I
-1700V
I
-1600V References
Fig. 2. Fluorescent intensity ! of the ionic beam versus the accelerating voltage. The measuring time was 400 s.
[1] S.L. Kaufman, Optics Comm. 17 (1976) 309.
307
Volume 31, number 3
OPTICS COMMUNICATIONS
[2] K.R. Anton, S.L. Kaufman, W. Klempt, G. Moruzzi, R. Neugart, E.W. Otten and B. Schinzler, Phys. Rev. Letters 40 (197q) 642. [3] Th. Meier, H. H6hnermann and H. Wagner, Optics Comm. 20 (1977) 397. [4] R.A. Holt, S.D. Rosner and T.D. Gailey, Phys. Rev. A 15 (1977) 2293; S.D. Rosner, T.D. Gailey and R.A. Holt, Phys. Rev. Letters 40 (1978) 851. [5] H. Winter and M. Gaillard, J. Phys. B: Atom. Molec. Phys. 10 (1977) 2739. [6] C. H~Jhle, H. Hiihnermann, Th. Meier and H. Wagner, Z. Physik A284 (1978) 261.
308
December 1979
[7] W.H. Wing, G.A. Ruff, W.E. Lamb and J.J. Spezeski, Phys. Rev. Lett. 36 (1976) 1488. [8] A. Carrington, P. Roberts and P. Sarre, Mol. Physics 34 (1977) 291. [9] S. Gerstenkorn and P. Luc, Atlas du spectre d'absorption de la molecule de l'iode (14800-20000 cm-1), editions du C.N.R.S., Paris (1978). [10] J. Bauche, C.R. Acad. Sc. Paris 263B (1966) 685..
OPTICS COMMUNICATIONS
December 1979
COLLINEAR LASER SPECTROSCOPY AT IONIC BEAMS OF ARGON AND CHLORINE A. EICHHORN, M. ELBEL and W. KAMKE Fachbereieh Physik tier UniversitatMarburg, D-3550 Marburg/Lahn, Fed. Rep. Germany and J.C. AMARI~ Departamento de Fi'sica Fundamental, Universidad de Zaragoza, Zaragoza-6, Spain Received 10 September 1979
Metastable ions of argon and chlorine were accelerated to form a beam which was led antiparallel to a dye-laser beam. When the laser beam was tuned to transitions from the metastables to higher states and the accelerating voltage was set to compensate for the remaining shift, fluorescence from the ions could be detected. Scanning the voltage excitation spectra of the ions could be obtained which allowed to determine the isotope shift of the lines the laser excited.
Since its first proposal [1] the dynamic reduction o f the Doppler width in fast beam collinear laser spectroscopy was verified at neutral alkalis [2] metastable ions [ 3 - 6 ] and molecules [7,8]. The choice of suitable ionic metastables is limited. It appears that the low energetic metastables of the earth alkalis and lanthanides are superior to the others concerning yield and narrow line width. This is due to their production in thermionic sources whose ionic temperatures are known to be low ( < 1 eV). Metastable ions of gases, howeverl have to be produced in discharges where the local variation of the potential at which the ions are born, contributes considerably to their velocity distribution and hence to the linewidth which can be obtained. Spectroscopic interest and the prospect to have a strong ionic beam pumped optically in flight for application with heavy ion accelerators led us to try chlorine and argon metastable ions as new examples. The ions were formed in an ionic source of the Penning type. A cylindrical anode was closed at both ends by flat metal sheets on cathode potential. One of the sheets which was made of tantalum was indirectly heated by thermal radiation and electron bombard306
ment so that an electron current of > 100 m A could be drawn from it. Argon or vapour o f carbon tetrachloride was admitted through a needle valve to the interior of the electrodes. An axial magnetic field of 100 Oe was applied. An anode voltage of 90 V and a discharge current of 300 mA yielded the maximum production of metastables ions. An ionic current of up to 10 - 5 A was drawn through an axial bore in the other cathode sheet. As the cathode was on ground potential the ions had to be accelerated into a chamber at high negative potential ( - 1 . . . - 3 keV). Into this chamber a line of post accelerating chambers was inserted. The ionic beam could be viewed by a multiplier through lateral holes in the chambers which were covered by thin wire mesh. Metastable argon ions in the state 3p 4 1D 3d 2G9/2 were excited b y laser light at X = 6117 A to the 3p4 1D 4p 2F7/2 state which by decaying to the 3p4 1D 4s 2D5/2 state yielded fluorescent quanta at X = 4611 )~ detected by the multiplier. Analogously, chlorine ions were excited from the metastable state 3p 3 4S 3d 5D 4 to 3p 3 4S 4p "SP3 at )t = 5423.25 )I, whence they decayed to 3p 3 4S 4s 5S 2 emitting light at X = 4795 )k which served for monitoring the excitation.
Volume 31, number 2
OPTICS COMMUNICATIONS
December 1979
l to v a c u u m pump Pe2nsllrce
i ~eCc~ I,ergJ~°n//
~
cl:cl:cX~SJmVe eI?r° t i°n
\ magneticfield / / <
i~'~O V){//4 k
V
,
~
/
F, ~ K ~ _ J .. ~-]l A~.,oov}J~lll II II II I ~/-,L, ,~
<
gas inlet F K A Z
7o°?iJ°ieam
/
window
• i/
_ _<:1. . . .
la~e~b~om
filter photomultiplier
filament cathode anode extractionelectrode Fig. 1. Experimental disposition.
The laser beam was sent antiparallel to the ionic beam. Its wave length was locked to a suitable iodine line whose wave lengths are known to great accuracy [9]. The absorption spectrum of the ions was scanned by sweeping the accelerating voltage. An example of the spectra obtained is given in fig. 2. The sensitivity was good enough to obtain clear spectra from 36Ar whose abundance in the used natural argon is only 0.3 percent. As a result, isotope shifts AVIS of argon and chlorine were obtained. We found
35C1
I
APIs(Ar ) = u(40Ar) - p(36Ar) = - 4 . 2 4 -+ 0.06 GHz APls(C1) = v(37C1) - u(35C1) = - 2 . 1 0 -+ 0.06 GHz. Both values are large and negative. They agree when reduced to equal difference of the atomic mass. They are apparently due to a strong specific mass effect to which the 3d electron gives rise by its momentum correlation with the inner p-shells [10]. No hyperfine splitting of the lines was observed the half width of the lines being 400 MHz. Apparently the hypeffine coupling of the 3p 3 shell which is coupled to a 4S state yields hyperfine splittings smaller than this figure. Thanks are due to Dr. D. Fick, Marburg, for his continuous interest. We acknowledge valuable help by Dr. He. Wagner, Marburg, in the construction and maintenance of the ionic source. Material support by the Deutsche Forschungsgemeinschaft is also acknowledged.
-2000V
I
-1900V
I
-1800V
I
-1700V
I
-1600V References
Fig. 2. Fluorescent intensity ! of the ionic beam versus the accelerating voltage. The measuring time was 400 s.
[1] S.L. Kaufman, Optics Comm. 17 (1976) 309.
307
Volume 31, number 3
OPTICS COMMUNICATIONS
[2] K.R. Anton, S.L. Kaufman, W. Klempt, G. Moruzzi, R. Neugart, E.W. Otten and B. Schinzler, Phys. Rev. Letters 40 (197q) 642. [3] Th. Meier, H. H6hnermann and H. Wagner, Optics Comm. 20 (1977) 397. [4] R.A. Holt, S.D. Rosner and T.D. Gailey, Phys. Rev. A 15 (1977) 2293; S.D. Rosner, T.D. Gailey and R.A. Holt, Phys. Rev. Letters 40 (1978) 851. [5] H. Winter and M. Gaillard, J. Phys. B: Atom. Molec. Phys. 10 (1977) 2739. [6] C. H~Jhle, H. Hiihnermann, Th. Meier and H. Wagner, Z. Physik A284 (1978) 261.
308
December 1979
[7] W.H. Wing, G.A. Ruff, W.E. Lamb and J.J. Spezeski, Phys. Rev. Lett. 36 (1976) 1488. [8] A. Carrington, P. Roberts and P. Sarre, Mol. Physics 34 (1977) 291. [9] S. Gerstenkorn and P. Luc, Atlas du spectre d'absorption de la molecule de l'iode (14800-20000 cm-1), editions du C.N.R.S., Paris (1978). [10] J. Bauche, C.R. Acad. Sc. Paris 263B (1966) 685..