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MULTIPHOTON ABSORPTION SPECTROSCOPY OF Li AND $Li_{2}$ USING A HEAT PIPE DIODE
M. H. Koch, C. B. Collins
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Abstract
A spectroscopic investigation of atomic and molecular lithium has been carried out in the region from 7150 {\\AA} to 2400 {\\AA} utilising a new detector device. This device, the heat pipe diode, employs the method of space charge ion detection in the heat pipe oven. CW and pulsed tunable dye lasers as well as classical light sources were used. One through four photon events were observed. Multiphoton absorption was observed in both the atom and molecule and a hybrid resonance involving both the atom and the molecule was observed. All the known molecular transitions were observed except the A-X transition (red bands). The weakness of the signal due to this band system made possible the observation of a new multiphoton molecular band system from 6000 {\\AA} to 5875 {\\AA} excited by a CW dye laser; with pulsed laser irradiation, this system expanded from 6210 {\\AA} to 5675 {\\AA}. The position of these bands agrees with a classical calculation of the overlap of the $^{3} \\Sigma^{+}_{u}$ and $^{3} \\Pi_{g}$ molecular states. The band structure might thus be attributed to a two photon molecular transition from the lowest $^{3} \\Sigma^{+}_{u}$ state to an unknown upper ungerade state with the $^{3} \\Pi_{g}$ state as a nearly resonate intermediate level.