1. Multi-step and Multi-photon Excitation Studies of Group-IIB Elements
ALI NADEEM
Laser Spectroscopy Laboratory
National Institute of Lasers and Optronics (NILOP)
Islamabad, Pakistan

2. Introduction
The bound states of Group II-B (Cd, Zn and Hg) are rarely studied, having similar ns2 configuration as Alkaline earth elements.
The resonance levels 1P1 lies in UV (Zn, Cd) and VUV (Hg), and ionization potentials are also very high ( 8-10 eV )
We have selected the 3P1 inter-combination level to approach the Rydberg states. The 3P1 level lie at lower energy as compare to 1P1
The fine structure energy difference is not very large therefore, the 3P0, 2 and 3D3 metastable state get populated due to collision energy transfer.
Consequently, one can observe the Rydberg states possessing larger J-values.

3. Rydberg States The states of high principal quantum number n.
Rydberg atom = Highly excited atom
Ionization threshold
Energy
Rydberg Formula (in a.u)

4. Multi-step and multi Photon laser excitation
The step-wise excitation is an excellent technique for the investigation of Rydberg States.
Rydberg states can be investigated which can not be probe by one photon transition.
Transitions that lie in the UV and VUV region can be approached using dye laser in visible and near UV region.
The spectral resolution depends on the line-width of the dye laser.
The step-wise excitation provides the maximum probability of exciting the atoms to the high lying states.

5. Schematic Diagram of the Experimental set-up

6. Thermionic Diode Ion Detector
Highly suitable device for measuring the line intensities, line shapes and high lying Rydberg states.
The collisional ionization of high-lying Rydberg levels is utilized in the thermionic diode.
3-5 A
Water cooling jackets
Buffer gas inlet
To vacuum pump
Cathode wire
Sample
Laser passage

7. Laser Spectroscopy laboratory at NILOP

8. Highly Excited States of Zinc

9. Multi-Step Laser Excitation from the 4s5s 3S1 excited state

10. Laser Excitation Spectra of Zinc

11. Excited states of Zinc from the 4s5s 3S1 excited state

12. Highly excited states close to the ionization threshold

14. Two-step excitation scheme for the investigation Rydberg states of Zinc1 S P o 10 20 30 40 50 60 70 80
Energy cm-1
X10 3 D 2 F
0, 1,2
1, 2,3
2, 3,4 l
= nm = nm
3P0,1,2
Selection rules:
4s 1S0

15. Spin-Orbit Interaction
Atomic No. of Zinc Z = 30
Atomic No. of Cadmium Z = 48
Atomic No. of Mercury Z = 80

16. Excitation Spectrum from the 4s4p 3P1,2,3 intermediate states of zinc

17. Excitation spectra of zinc, the series convergence from the 4s4p 3P0,1,2 excited states

18. Highly excited states of Zn close to the ionization limit excited from the 4s4p 3P1 state

19. Three-step laser excitation spectra of zinc from the 4s4d 3D1,2,3 states
cm-1
4s4d 3D1,2, cm-1
cm-1

20. Highly Excited states of zinc at different pressure at 3 and 10 mbar

21. Ionization Potentials of Zinc
4snp 3P2 (12 ≤ n ≤ 60) , ± 0.05 cm-1
4snd 3D2 (14 ≤ n ≤ 55), ± 0.05 cm-1

22. Highly Excited States of Cadmium

23. Two-step excitation spectra of Cadmium
72225
72250
72275
72300
72325
72350
72375
200
300
400
500
600
700
800
900
23d 1 D 2
27d 3
481nm
27s S
Ionization Signal(arb.units)
Term Energy cm -1
23s
480nm
21d

24. Highly Excited States of Cadmium

25. Absorption Spectroscopy
Multi-step laser excitation of the odd-parity 5snℓ (ℓ = 3) states of neutral cadmium
Absorption Spectroscopy
cm-1
5s5d 3D1,2, cm-1
cm-1
cm-1
5s5d 3D1,2, cm-1
cm-1
The spectrum of cadmium showing the 5snf 3F3 (14  n  21), 5snf 3F4 (14  n  21), 5snf 3F2 (14  n  20) and 5snd 3P1 (16  n  27) Rydberg series excited from the 5s5d 3D1,2,3 multiplet.

26. Highly Excited States of Cadmium

28. Ionization Potentials of Cadmium
5snd 3D2 (11 ≤ n ≤ 52) Ionization Energy ± 0.13 cm-1
5sn f 3F3 (12 ≤ n ≤ 52) Ionization Energy ± 0.13 cm-1

29. Two-step laser excitation spectrum of Hg
(5) cm-1 nm
6s6p 3P1
cm-1
λ = nm
6s2 1S0

30. International Publication
Two-step laser spectroscopy of the highly excited states of cadmium
Ali Nadeem, M Nawaz, S A Bhatti and M A Baig
J. Phys. B: At. & Mol. Opt. Phys. 38 (2005)
2. Two-step laser excitation of the 4snd 3D1,2,3 and 4sns 3S1 states from the 4s4p3P1 level in zinc
J. Phys. B: At. & Mol. Opt. Phys. 39 (2006)
3. Multi-step laser excitation of the highly excited states of zinc
Optics Communications 259 (2006)
4. Two-step laser excitation of the highly excited even-parity states of atomic murcury
Ali Nadeem, M Nawaz, S. U. Haq, S. Shahzada, S A Bhatti and M A Baig
Eur. Phys. J. D. (2009) 53,
5. Oscillator strength measurements from the 4s4p 3P1
4snd 3D2 excited state of zinc.
S. U. Haq, Ali Nadeem, M. Nawaz and M.A Baig
J. Opt. Soc. Am. B (2010) 27,
6. Oscillator strength measurements of the 5s5p 3P snd 3D2 Rydberg transitions of cadmium.
Ali Nadeem and S. U. Haq
Spectrochimica Acta Part B 65, (2010)

31. Continu……
7. Three - step laser excitation of the odd-parity 5s5d 3D →5snf 3F states of cadmium
Ali Nadeem, M Shah, S U Haq, S Shahzada, M Mumtaz, A Waheed, M Nawaz,
M Ahmed and M A Baig
Eur. J. Phys. D. 68, (2014) 192
8. Three-step laser excitation of the odd-parity 4s4d 3D →4snf 3F states of zinc
Ali Nadeem, M. Shah, S. U. Haq and M A Baig
Submitted: (Spectrochimica Acta Part B 2016)

33. Thank you
NILOP