Milton Birnbaum

Highly efficient Nd:YVO4 diode‐laser end‐pumped laser

We report on the first diode‐laser (nominal 200‐mW 10‐stripe laser diode) end‐pump lasing of Nd:YVO4. The lowest threshold (30 mW) and highest output power (120 mW) were observed from the Nd:YVO4 laser as compared to a similar Nd:YAG laser. Over 50% optical slope efficiency was obtained, the highest yet reported for diode pumping. This device performed at a 10% overall efficiency. Measurements over a 21‐nm range show the advantages of the Nd:YVO4 pump absorption band.

Stimulated‐emission cross section at 1064 and 1342 nm in Nd : YVO4

The stimulated‐emission cross sections at 1064 (4F3/2→4I11/2) and 1342 nm (4F3/2→4I13/2) in Nb : YVO4 were determined by measurement of laser thresholds as a function of output mirror reflectivity. Small samples of Nd : YVO4 and Nd : YAG were end pumped at room temperature with a cw 514.5‐nm argon ion laser in an almost identical geometrical arrangement which permitted comparative values to be obtained. Assuming that the pumping quantum efficiency of Nd : YVO is similar to that of Nd : YAG, the stimulated‐emission cross sections obtained for the 1064‐ and 1342‐nm transitions were respectively 12×10−19 and 6.0×10−19 cm2.

Fluorescence of Atmospheric Aerosols and Lidar Implications

The fluorescence of aerosols in the ambient atmosphere has been monitored in situ using cw argon ion laser excitation in bands of 50 nm and 100 nm over the spectral region of 560-810 nm. The observed broadband aerosol fluorescence may limit lidar (laser radar) determinations of pollutants. The limitation can be overcome by a method in which the aerosol fluorescence excited at two wavelengths is constant while the molecular signals differ. The effectiveness of the technique has been demonstrated by in situ measurements of atmospheric nitrogen dioxide (NO(2)) in the presence of aerosols.

Continuous‐wave operation of Nd : YVO4 at 1.06 and 1.34 μ

Continuous‐wave plane‐polarized outputs of 1 W at 1.06 μ and 0.35 W at 1.34 μ were obtained by end pumping small samples of Nd : YVO4 with an argon‐ion laser. Slope efficiencies and material losses were determined. At 1.06 and 1.34 μ, Nd : YVO4 lasers can substantially outperform Nd : YAG lasers. Self‐Q‐switched operation of Nd : YVO4 at both wavelengths was obtained by resonator misalignment.

Laser emission cross section of Nd:YAG at 1064 nm

The stimulated emission cross section of Nd:YAG (yttrium aluminum garnet) (4F3/2→4I11/2) was compared to the known cross section of Nd:ED‐2 glass at 1060 nm. Small samples of Nd:YAG and ED‐2 glass were end pumped with a chopped cw 514.5‐nm argon‐ion laser in an identical geometrical arrangement. The stimulated emission cross section obtained for Nd:YAG at 1064 nm was found to be 7.6 ×10−19 cm.

Fluorescence determination of atmospheric NO2

The concentrations of nitrogen dioxide (NO2) in the atmosphere have been determined in real time and with a sensitivity of one part per billion. Laser excitation of NO2 was at 4416 and 4880 Å and fluorescence was monitored at 0.7 to 0.8 μm. Results obtained on typical smoggy days in Los Angeles are presented.

Stimulated‐Emission Cross Section of Nd3+ at 1.06 μ in POCl3, YAG, CaWO4, ED‐2 Glass and LG55 Glass

Stimulated‐emission cross sections of Nd3+ at 1.06 μ in POCl3, yttrium aluminum garnet (YAG), calcium tungstate (CaWO4), and two laser glasses (ED‐2 and LG55) were measured by studying the laser threshold gain and inverted population. The technique of end pumping with pulsed xenon ion lasers was used with an identical laser cavity for all the Nd‐doped samples. A direct comparison of the cross sections in the different hosts was obtained.

Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues

The cw and Q-switched performance of Er:YAG lasers operating at 1645 nm were measured. Guided by previous work in the literature, we sought to improve efficiency at low pulse repetition frequencies by decreasing the doping level from 0.5 to 0.25 at.% to reduce upconversion losses. Only a small improvement was obtained with this first-time-tested lower-doped material. Measurements of the fluorescence due to upconversion directly indicated that loss due to this process could not account for the observed power loss at low pulse repetition frequencies. Enhanced green emission during Q-switched operation, resulting from two-photon absorption of 1645 nm intracavity laser light, is reported for what we believe to be the first time. Measurements indicated that the output loss from this process is negligible.

Lifetimes of the 4F3/2 state in Nd : YVO4

The fluorescence lifetime of the 4F3/2 state of Nd3+ in YVO4 crystals has been determined as a function of temperature and concentration. Over the temperature range 90–300 °K the lifetime is approximately 100 μsec and decreases to 87 μsec at 453 °K. The lifetime at 300 °K is found to depend on the Nd3+ concentration decreasing from 100 μsec at 0.4 at.% to 60 μsec at 1.6 at.%.

Atmospheric NO 2 determination by 442-nm laser induced fluorescence

An atmospheric monitor with a detectability of 0.6 ppbv, utilizing a compact He-Cd laser at 442 nm for excitation of the NO(2) molecules is described. Photon-counting techniques were employed to detect the NO(2) fluorescence transmitted through a bandpass liquid solution filter that did not fluoresce upon absorption of scattered laser light. Operational characteristics of the instrument are described. Results obtained in ambient air monitoring are presented.