Bruce H. T. Chai

1.047-/spl mu/m Yb:Sr/sub 5/(PO/sub 4/)/sub 3/F energy storage optical amplifier

The pumping and gain properties of Yb/sup 3+/-doped Sr/sub 5/(PO/sub 4/)/sub 3/F (Yb:S-FAP) are reported. Using a tunable, free running 900-nm Cr:LiSAF oscillator as a pump source for a Yb:S-FAP rod, the saturation fluence for pumping was measured to be 2.2 J/cm/sup 2/ based on either the spatial, temporal, or energy transmission properties of the Yb:S-FAP rod. The emission peak of Yb:S-FAP (1047.5 nm in air) is shown to overlap with that of Nd:YLiF/sub 4/ (Nd:YLF) to within 0.1 nm, rendering Yb:S-FAP suitable as an effective power amplifier for Nd:YLF oscillators. The small signal gain, under varying pumping conditions, was measured with a cw Nd:YLF probe laser. These measurements implied emission cross sections of 6.0/spl times/10/sup -20/ and 1.5/spl times/10/sup -20/ cm/sup 2/ for /spl pi/ and /spl sigma/ polarized light. Respectively, which fall within the error limits of the previously reported values of 7.3/spl times/10/sup -20/ and 1.4/spl times/10/sup -20/ cm/sup 2/ for /spl pi/ and /spl sigma/ polarized light, obtained from purely spectroscopic techniques. The effects of radiation trapping on the emission lifetime have been quantified and have been shown to lead to emission lifetimes as long as 1.7 ms, for large optically dense crystals. This is substantially larger than the measured intrinsic lifetime of 1.10 ms. Yb:S-FAP crystal boules up to 25/spl times/25/spl times/175 mm in size, which were grown for the above experiments and were found to have acceptable loss characteristics ( >

Flashlamp-pumped laser performance of LiCaAIF6:Cr3+

The results of flashlamp pumping of the LiCaAIF6:Cr3+ (Cr:LiCAF) laser crystal are reported. We have so far obtained slope efficiencies as high as 1.55% in a close-coupled, diffusely reflecting cavity. Based on the measured insertion loss of the presently available material, we predict that an efficiency of about 4% will be obtained when low-loss material becomes available. This extrapolated efficiency is comparable with the performance of a high-quality alexandrite laser rod in the same apparatus.

New ytterbium-doped apatite crystals for flexible laser design

A new class of Yb-lasers is summarized in this article. The apatite family of crystals has been found to impose favorable spectroscopic and laser properties on the Yb{sup 3+} activator ion. Crystals of Yb-doped Ca{sub 5}(PO{sub 4}){sub 3}F, Sr{sub 5}(PO{sub 4}){sub 3}F, Ca{sub x}Sr{sub 5{minus}x}(PO{sub 4}){sub 3}F, and Sr{sub 5}(VO{sub 4}){sub 3}F have been grown and investigated. Several useful laser crystals have been identified which offer a variety of fundamental laser parameters for designing diode-pumped systems. In general, this class of materials is characterized by high emission cross sections (3.6--13.1 {times} 10{sup {minus}20} cm{sup 2}), useful emission lifetimes (0.59--1.26 msec), a strong pump band ({sigma}{sub abs} = 2.0--10.0 {times} 10{sup {minus}20} cm{sup 2}) and pump and extraction wavelengths near 900 and 1,045 nm, respectively. Efficient lasing has been demonstrated for several of the members of this class of materials, and high optical quality crystals have been grown by the Czochralski method.

Laser Performance and Optical Properties of LiSrGaF6:Cr3+

The laser-pumped laser performance of the new material LiSrGaF6:Cr3+ has been characterized. The laser results indicate that the material operates with a high slope efficiency of 50% due to the low passive, and pump-induced, loss levels. The optical and laser properties of Cr3+-doped LiSrGaF6 are similar to those of the LiSrAlF6 host previously investigated, although the magnitude of the expansion coefficients of the gallium analog are more favorable.

Laser Performance and Spectroscopy of Cr3+ in LiCaAlF6 and LiSrAlF6

We comprehensively report on the laser measurements and relevant spectroscopic properties of the materials LiCaAlF6:Cr3+ (Cr:L1CAF) and L1SrAlF6:Cr3+ (Cr:LiSAF). Laser-pumped laser measurements show that slope efficiencies of >50% are attainable with currently available Cr:LiCAF material, and that efficiencies of 67% should ultimately be achievable. Efficiencies of 36% have been measured for Cr:LiSAF. The absorption and emission properties, and the direct measurements of the excited state absorption loss, support the data concerning the lasing efficiencies and tuning ranges. Flashlamp-pumped operation of Cr:LiCAF has provided electrical efficiencies of 1.55% thus far, and we expect to obtain performance comparable to that of alexandrite in the future (which is 4% efficiency 1n the present apparatus).