X. X. Zhang

Laser performance of Cr4+:Y2SiO5

Laser action in Cr4+ doped yttrium‐orthosilicate Cr4+:Y2SiO5 cooled to 77 K was demonstrated for the first time with 1064 and 532 nm pumping from a pulsed Nd:YAG laser and broad band (@ 840 nm) pumping from a Q‐switched Cr:LiSAF laser.

LUMINESCENCE OF CR3+ AND ENERGY TRANSFER BETWEEN CR3+ AND ND3+ IONS IN YTTRIUM ALUMINUM GARNET

The luminescence properties of Cr3+ ions and the energy transfer between Cr3+ and Nd3+ ions have been studied quantitatively in yttrium aluminum garnet (YAG). The energy level diagram and the emission spectrum of 4T2→4A2 transition of Cr3+ ions were calculated in this crystal using the single‐configurational‐coordination model and the absorption data. Our calculated Δ value (the energy difference between the 2E zero‐vibrational level and the crossover point of 2E and 4T2 states), ∼730 cm−1 at room temperature, in contrast to the previously estimated value of ∼1000 cm−1, accounts for a variety of experimental results more satisfactorily. Both the 4T2 and 2E states of Cr3+ ions were found to contribute to the energy transfer to Nd3+ ions. The contribution of the former dominates at high temperatures and the latter at low temperatures. The thermal population distribution between the 4T2 and 2E states of Cr3+ ions was shown to be responsible for the temperature dependences of the Cr3+ luminescence properties ...

Efficient laser performance of Nd3+:Sr5(PO 4)3F at 1.059 and 1.328 μm

High efficiency, low threshold laser performance of Nd3+ doped Sr5(PO4)3F, or S‐FAP, crystals has been demonstrated. Its performance and properties compared with commercially available Nd:YVO4 indicate that Nd:S‐FAP is an outstanding medium for diode pumped laser applications at both 1.059 and 1.328 μm.

Growth of laser‐quality single crystals of Nd3+‐doped calcium fluorapatite and their efficient lasing performance

The Czochralski growth of laser‐quality Nd3+‐doped calcium fluorapatite single crystals and their lasing characterization are reported. Low threshold and high efficiency lasing performances were achieved in both continuous‐wave and long pulse laser‐pump‐laser operation. The effect of concentration quenching on laser performance is discussed.

Ho3+ to Yb3+ back transfer and thermal quenching of upconversion green emission in fluoride crystals

Energy transfer from Ho3+ to Yb3+ has been demonstrated in fluoride crystals such as KYF4, BaY2F8, and LiYF4. This transfer was found to occur above a certain temperature and its efficiency increases with temperature. It accounts for the thermal quenching of green emission from upconverted Ho3+ and partly explains the failure, to date, to obtain room temperature, Yb3+ sensitized Ho3+ upconversion lasers in these three hosts. Low Yb3+ concentration is suggested for future attempts to achieve room temperature Yb3+, Ho3+ upconversion green laser operation of these crystals.

Broadband, intensity dependent absorption in tetravalent chromium‐doped crystals

Cr4+‐doped Y2SiO5 and Ca2Al2SiO7 have been investigated as broadband, solid state saturable absorbers. Saturation properties in the near infrared as well as a demonstration of tunable, passive Q switching of a flash‐lamp pumped Cr:LiSAF laser are discussed.

SPECTROSCOPIC CHARACTERISTICS OF ND3+-DOPED STRONTIUM FLUOROVANADATE AND THEIR RELATIONSHIP TO LASER PERFORMANCE

High slope efficiency and low threshold laser performance have been achieved for both long pulsed and cw operation at 1.065 μm in Nd3+‐doped strontium fluorovanadate crystal, Nd3+:Sr5(VO4)3F, when pumped by narrow band pulsed Cr:LiSAF and cw Ti:sapphire lasers. However, there are inequivalent Nd3+ sites in the crystal. The absorption of Nd3+ ions in secondary sites, sites other than the site which contributes to lasing, may reduce the pumping efficiency and, consequently, the lasing efficiency. Strong concentration quenching of the Nd3+ 4F3/2 state was also observed reducing the quantum efficiency of the laser transition from this state.

Lamp‐pumped laser performance of Nd3+:Sr5(PO4)3F operating both separately and simultaneously at 1.059 and 1.328 μm

Lamp‐pumped laser performance of Nd3+‐doped strontium fluorapatite, Sr5(PO4)3F or S‐FAP, has been characterized and compared with that of Nd3+‐doped yttrium aluminum garnet (YAG) at both 1.06 and 1.3 μm. Nd3+:S‐FAP was found to exhibit lower thresholds and lower slope efficiencies than Nd3+:YAG. The former is attributed to the higher emission cross section, and the latter to lower Nd3+ concentration in S‐FAP. The 1.3 μm lasing of Nd3+:S‐FAP is of particular interest because of its high emission cross section (2.4×10−19 cm2). Q‐switched and dual‐wavelength lasing operation were also demonstrated in Nd3+:S‐FAP.

Efficient laser performance of Nd:GdLiF4 : a new laser crystal

Laser action of Nd3+ doped GdLiF4 (GLF) has been demonstrated for both pulsed and cw laser pumped operation. A slope efficiency of 60% was obtained in either manner of operation. The spectroscopic properties and laser performance of Nd:GLF are very similar to those of Nd:YLF. GLF, on the other hand, can be doped with much higher Nd3+ concentration.

MULTISITE NATURE AND EFFICIENT LASING AT 1041 AND 1302 NM IN ND3+ DOPED POTASSIUM YTTRIUM FLUORIDE

Lasing of Nd3+ ions in different crystallographic sites of KYF4 has been demonstrated to occur at different wavelengths. Low threshold, high efficiency lasing performance at 1041 and 1302 nm were achieved under selective pumping conditions. The stimulated emission cross section at 1041.2 nm was estimated to be 2.6×10−19 cm2 and the radiative lifetime was found to be 600 μs.