Pulsed-periodic laser on RM helium and strontium transitions

Abstract

621.375.826 Conditions of generation of a running excitation wave in the active medium of gas lasers and efficiency of the running wave application for pumping of the active medium are considered by the example of a strontium vapor laser. It is demonstrated that the running excitation wave is generated directly in the active laser medium and is supported by the energy stored in the capacitive component of the impedance of a gas-discharge tube. Generation on the self-limited (2 1 P 1 -2 1 S 0 ) transition of the helium atom at λ = 2058 nm and simultaneous generation on RM transitions of the strontium ion and strontium and helium atoms and on a number of neon atom transitions is first excited.It is well known that phantom currents are observed in active media of lasers on RM (from resonant to metastable energy levels) transitions of metal atoms [1]. Investigations into the nature of phantom currents have demonstrated that this current is caused by the charge displacement in the active laser medium when the capacitive components of the impedance of the laser discharge circuit and gas-discharge tube (GDT) are charged. In the presence of the phantom current, the active medium is under the same potential, which does not allow pre-pulsed plasma electrons to store energy sufficient for inelastic collisions in the active medium [2,3]. An analysis of the processes occurring in the active medium and discharge laser circuit in the presence of the phantom current has demonstrated that a longitudinal excitation wave, arising in the active laser medium under certain conditions, is supported by the energy stored in the capacitive component of the gasdischarge tube impedance. In the present work, conditions of generation of the longitudinal excitation wave in the active medium and efficiency of its application for pumping of gas lasers are considered on the example of a strontium vapor laser.The typical design of the gas-discharge tube for lasers on RM transitions of metal atoms comprises a vacuum coating in which a thermally insulated gas-discharge channel formed by a ceramic tube is located. Cylindrical electrodes are at the ends of the gas-discharge channel in cold buffer zones [4,5]. Figure 1 shows the pump generator design circuit for a metal vapor laser with the equivalent GDT circuit framed by the dashed curve. If we fill the gas-discharge tube with an inert gas, for example, helium and initiate a pulsed-periodic discharge with high pulse repetition frequency of ~10 kHz, the discharge channel will be heated at the expense of dissipation of energy stored in the discharge, thereby resulting in changes of the helium atom concentration in the discharge channel and cold buffer zones proportional to the temperature difference. In this case, the cylindrical GDT cathode will also be heated because of the presence of the intrinsic capacitive component which determines its thermal emission characteristics. Under such conditions, the discharge of the storage capacitor will be accompanied by simultaneous charge of all capacitive c...

Spatiotemporal spectroscopic diagnostics of a pulse-periodic strontium vapor laser

“…Lasing on three more SrI transitions at ~3 μm with pulse duration of ~50 ns delayed by ~40 ns from the onset of lasing on the above-indicated transitions was also observed during the current pulse; the mechanism of forming the inverse population on these transitions was discussed in [2]. Under conditions of discharge excitation close to those reported in [1], lasing on the r-m transition of the HeI atom at λ = 2.06 μm and on several NeI atomic transitions in the wavelength range 1.08-1.52 μm was excited in [3] in the mixture of neon with helium (at a total pressure of ~200 mm Hg). Lasing on HeI and NeI lines as well as on SrI and SrII lines was observed during the current pulse.…”

“…We note that lasing on lines of the buffer gas at sufficiently high pressure in the He-Ne-Sr laser can be excited only in the presence of the Sr atoms delivered from the hot walls of the gas-discharge tube (GDT). This conclusion was made by Chebotarev et al [4] who demonstrated that under conditions of discharge excitation close to those of [1][2][3], the presence of the Sr atoms with the concentration ~4·10 14 cm -3 prevents contraction of the pulse-periodic discharge inevitable for sufficiently high pressure in the hot GDT.…”

The strontium-vapor laser pumping efficiency under running-wave excitation

“…In the case where the second and the third circuits are eliminated from the pump system of the active laser medium, using, say, the self-capacitance of the gas-discharge tube as a storage capacitor, an RM laser efficiency of ~10% (~6-8% for a strontium-vapor laser) can be obtained. A laser efficiency as high as this suggests that the average lasing power can be increased by an order of magnitude as compared to the currently available power level and multiple-wavelength lasers can be developed [24]. This shows good promise for development of lasers on RM transitions of metal atoms.…”