Volume 57, number 6 OPTICS COMMUNICATIONS 15 April 1986 THE ABSORPTION AND EMISSION OBSERVATIONS OF THE SODIUM NEAR-INFRARED SPECTRUM Marija PALLE ‘, Slobodan MILOSEVIC, Damir VEiA and Goran PICHLER Insiitute of Physics of the University, Unioersity of Zagreb, Bijenitkka 46, POB 304, Zugreh, Yupduoru Received 10 December 1985 The absorption and emission spectra of dense sodium vapour have been measured between 790 nm and 1000 nm. In the emission spectrum from the high-pressure sodium lamp we observed the characteristic continuum structure at X82 nm which we interpreted as a satellite band originating from the 1 ‘El -1 3x: transition. The complementary absorption measurements in very dense sodium vapour revealed only certain structures near the head of heads of the A-X molecular band, but not a continuous band at 882 nm. 1. Introduction Reliable spectroscopic data for lighter alkali dimers zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF (Li, , Na, and K2) are available mainly for singlet states. There is an impressive number of papers devot- ed to different experimental and theoretical aspects of these singlet states [l]. On the other hand, there is relatively small number of measurements and experi- mental data which involve the lowest triplet potential curves for lithium [2,3], sodium [4-81 and potas- sium [9-l l] dimers. However, the satellite bands originating from the 1 311g-1 3Xi transitions have been observed and interpreted in lithium [2], sodium [5,6] and potassium [lo] dimers. High quality cal- culations of the lithium and sodium dimer potential curves [ 121 greatly facilitated the interpretation of the observed triplet transitions. Unfortunately, the identification of the 1 3 Xi-1 3 Ci transition caused much more difficulties. Several years ago Bhaskar et al. [9] reported the observations of the 1 3Xi-1 3Zi bands in potassium in the region beyond 1 pm. Very recently, Huennekens et al. [ 1 l] performed absorp- tion, thermal emission and laser induced fluorescence measurements in sodium and potassium vapours using specially designed alkali jet apparatus. Their measure- ments and interpretation ruled out Vasilakis et al. ’ Present address: Faculty of Technology, Pierottijeva bb. 41000 Zagreb, Yugoslavia. [4] and Bhaskar et al. [9] identification of these con- tinuous bands in sodium and potassium cases. In order to further contribute to the identification of this band from the lowest triplet transition exci- mer, we performed complementary absorption and emission measurements of sodium near-infra red spec- trum using the heat-pipe oven for absorption, and high-pressure discharges for emission measurements. Our results confirmed measurements and conclusions of Huennekens et al. [l l] and identified the observed band at 882 nm as the satellite band from the 1 ‘Xi- 1 3 ZZA transition. The increasing interest in triplet al- kali spectra and potential curves is connected with possibility to use alkali dimers as the laser medium in the near infra-red spectral region, where continuous. ly tunable lasers are not currently available [ 14- 161. The lowest allowed triplet transition has been theo- retically investigated by Konowalow and Julienne [14] as possible candidate for the laser action in near ir. Shahdin et al. [15] observed laser induced fluores- cence emission at 855.5 nm, by using excimer laser at 35 1 nm for excitation. They interpreted the band as coming from the 1 3 Xi-1 3X’, transition. Quite recently, Dinev et al. [ 161 observed superradiant uni- directional emission within a broad band at 830 nm, attributing it to the same lowest transition triplet. They have excited sodium vapour by means of the pulsed dye laser with rhodamine 6G dye. In both ex- periments the population mechanism of the upper 394 0 030-4018/86/$03.50 OElsevier Science Publishers B.V. (North-Holland Physics Publishing Division)