One- and two-photon laser optogalvanic spectroscopy of neon in the 570–626 nm region R. Omidyan a , F. Fathi a , H. Farrokhpour a,b, * , M. Tabrizchi a a Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran b Department of Chemistry, Faculty of Science, Yazd University, Safaieh, Pajoohesh Street, Yazd 89195-741, Iran article info Article history: Received 2 March 2008 Received in revised form 26 June 2008 Accepted 28 July 2008 abstract Eleven two-photon transitions originating from the 2p 5 3s[3/2] 2 , 2p 5 3s 0 [1/2] o , 2p 5 3s[3/2] 1 , and 2p 5 3s 0 [1/ 2] 1 states to the 2p 5 4d configuration states have been investigated in the optogalvanic spectrum of neon in the visible region (570–626 nm) for the first time. The two-photon assignments are confirmed by eval- uating the temporal evolution, power dependency, and line widths of the optogalvanic signals. The time evolution of the optogalvanic signals for the two-photon transition originating from the metastable 2p 5 3s[3/2] 2 state to the 2p 5 4d 0 [3/2] 2 state has also been studied at different discharge currents. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Laser optogalvanic spectroscopy is widely used in a variety of spectroscopic investigations and techniques including plasma diagnostics [1], atomic and molecular spectroscopy [2,3], Penning ionization spectroscopy [4], Doppler-free spectroscopy [5], popula- tion inversion [6], and Rydberg-states spectroscopy [7]. Optogalvanic (OG) spectra for the calibration of laser wave- length can provide very accurate wavelength markers, good to at least six significant digits. The OG effect relies on standard electri- cal measurement techniques avoiding optical problems such as la- ser elastic background and collection efficiency. Consequently, it can detect weak transitions with high signal to noise ratio. Briefly, the OG effect is the change in the voltage applied on a gas filled electrical discharge and in the impedance through it, due to changes in the effective ionization rates induced by laser light tuned resonantly to specific atomic or molecular transition of the discharge medium. Such a laser illumination usually causes an increase in the population of the highly excited levels which en- hances the ionization and causes a voltage drop. The direction of voltage change is primarily determined by the lifetime of the lower of the two states involved in the optical transition [8,9]. Over the years, many investigations have been carried out to observe the OG lines of noble gases such as neon and argon extend- ing from the ultra-violet to the red spectral region [11,12]. The OG spectroscopy of neon in the 337–598 nm region has been reported by Zhu et al. using a commercial Fe–Ne hallow cathode lamp [13]. Recently, Alnama et al. observed new OG Rydberg–Rydberg transi- tions of neon in the near-infrared region (830–870 nm) using a commercial Fe–Ne hollow cathode lamp [14]. They observed tran- sitions from the 2p 5 3d[3/2] 1 and 2p 5 3d[7/2] 3,4 states (according to the JK coupling scheme described later) to high-lying nf states. They also observed other OG transitions in the blue range between 380 and 420 nm. These OG transitions have been completely as- signed to ns, nd, ns 0 , and nd 0 Rydberg series excited from the 2p 5 3p[1/2] 1 and 2p 5 3p[5/2] 2,3 levels of neon. Two-photon OG spectroscopy of neon has also been studied by several researchers [10,15–18]. In this case, the OG signal is iden- tified via a two-step excitation involving a virtual intermediate state. Narayanan et al. have studied the two- and one-photon OG spectra of neon in the 610–730 nm region using an Nd–YAG- pumped dye laser and a commercial Fe–Ne hallow cathode lamp [15]. The two- and one-photon OG spectroscopy of neon in the 410–545 nm region has also been recorded by Kumar et al. using Fe–Ne hallow cathode lamp and an excimer laser-pumped dye la- ser [10]. A systematical investigation of one- and two-photon neon and argon OG spectra in the 735–781 nm spectral region has been reported by Tang and Miles [16]. They observed two-photon tran- sitions from 2p 5 3s[3/2] 1 , 2p 5 3s 0 [1/2] 0 and 2p 5 3s 0 [1/2] 1 states to Rydberg states of the 2p 5 3d configuration. Thukur and Narayanan also observed the two-photon transitions from the metastable 2p 5 3s[3/2] 2 state to higher Rydberg states (2p 5 ns[3/2] 2 with n P 7 and 2p 5 nd[3/2] 2 with n P 6) of neon in the OG spectrum be- tween the 500 and 548 nm region [17]. Piracha et al. reported extensive new data on the two-photon OG spectrum of neon in the 479–553 nm in the visible region [18]. They observed four Ryd- berg series originating from the metastable 2p 5 3s[3/2] 2 state to 2p 5 ns[3/2] 2 , 2p 5 nd[7/2] 3,4 , 2p 5 nd[5/2] 2,3 and 2p 5 nd 0 [3/2] 2 states with n P 6 as well as two more Rydberg series originating from the non-metastable 2p 5 3s[3/2] 1 state to 2p 5 ns 0 [1/2] 1 and 2p 5 nd 0 [5/2] 2,3 states with n P 6. Transitions from the metastable 0030-4018/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2008.07.072 * Corresponding author. Address: Department of Chemistry, Faculty of Science, Yazd University, Safaieh, Pajoohesh Street, Yazd 89195-741, Iran. Tel.: +98 351 8211670 2641; fax: +98 3518210644. E-mail address: farrokhphossein@gmail.com (H. Farrokhpour). Optics Communications 281 (2008) 5555–5560 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom