Low-threshold wide-band lasing was achieved for a YAG crystal with optically and thermally stable color centers. The absorption and luminescence spectra were determined, and the gain was measured in the range of wavelengths corresponding to the color-center luminescence. The cross section of the lasing transition was estimated (8 × 10−19 cm2) and the efficiency of conversion of the pump radiation from a neodymium laser into the output radiation was determined (10%).

Lasing due to impurity color centers in yttrium aluminum garnet crystals at wavelengths in the range 1.35-1.45 μm

A diode-pumped highly efficient Cr4+:YAG passively Q-switched Nd:GdVO4 laser formed by a plano–concave resonator has been demonstrated. At the highest attainable absorbed pump power of 11.4 W, 4.05 W of average output power, which was two thirds of the maximum corresponding cw output, was achieved with an optical conversion efficiency of 35.5%, and the slope efficiency was determined to be 46.8%, reaching 85% of the magnitude of its cw counterpart. The resulting shortest pulse duration, single-pulse energy, and peak power were found to be 13 ns, 90 μJ, and 7 kW, respectively, with a pulse repetition frequency (PRF) of 45 kHz. Two particularly modified resonator configurations were employed; the largest pulse energy and the highest peak power reached were, respectively, 154 μJ and 11.2 kW at 8.5 W of absorbed pump power. An analytical relation between the PRF and the absorbed pump power is given for a passively Q-switched laser, showing good consistency with experiment with a Nd:GdVO4 laser. The dependence of the operational parameters on the pump power and on the output coupling was also investigated experimentally. Issues involving the criterion for passive Q switching are discussed in some detail for Cr4+:YAG passively Q-switched neodymium-doped vanadate lasers.

Efficient passive Q-switching operation of a diode-pumped Nd:GdVO 4 laser with a Cr 4+ :YAG saturable absorber

Lasers and Coherent Light Sources

A compact pulsed Nd:LuAG laser at 1064 nm based on the self-Q-switching technique is reported, having the output power as high as 6.61 W at the incident pump power of 21.32 W, corresponding to the optical conversion efficiency of ∼31%. The temporal width of the pulse was in the range from 532.2 to 652.6 ns, and the repetition rate varied between 488.6 and 551.9 kHz. To the best of our knowledge, this is the first report on the self-Q-switching Nd:LuAG laser. With the nonlinear refractive index calculated to be 1.8 × 10–19 m2/W, and the numerical simulation made with the modified rate equations, the Kerr lens effect was believed to be the reason for the self-Q-switching of Nd:LuAG. The compact cavity generating pulses with high output power and high repetition rate not only reveal that the self-Q-switching technique could be an efficient method for the generation of pulses with high output power and high repetition rate, but enrich the characteristics of Nd:LuAG crystal.

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High Power Self-Q-Switching in Nd:LuAG Laser

Refractive-index changes accompanying changes in population of electronic levels of Yb3+ ions in a Yb:YAG laser disk under intense diode and laser pumping have been studied by use of both a highly sensitive polarization interferometer and transient grating testing at 633 nm. The electronic change of the index that is due to excitation of the Yb3+ ions (which have different polarizability of ground state 2F7/2 and excited level 2F5/2) is strongly predominant over the thermal component. The polarizability differences are deltap (1.9 +/- 0.8) x 10(-26) and (1.95 +/- 0.25) x 10(-26) cm3 as measured at 633 nm in interferometric and transient grating experiments, respectively.

Electronic mechanism for refractive-index changes in intensively pumped Yb:YAG laser crystals.

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr4+:YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 µm with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr4+:YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers.

Passively Q-switched Yb:YAG laser with Cr 4+ :YAG as the saturable absorber

By use of a laser diode as a pump source, a self-Q-switched laser from a Cr,Nd:YAG crystal is demonstrated. The output Q–switched traces are very stable, the threshold pump power is 3.5 W, the pulse duration is 50 ns, and the slope efficiency is as high as 20%. In addition, the pulse width remains constant while the pulse repetition rate varies with pump power.

Laser-diode-pumped Cr 4+ ,Nd 3+ :YAG with self-Q-switched laser output of 1.4 W

Spectral properties of Nd:Sr(1-x)Y(x)F(2+x) crystals were investigated. Compared with Nd:SrF2, the spectral parameters of Nd:Sr(1-x)Y(x)F(2+x) (x=0.05,0.1) were altered in a large scale. LD-pumped true CW laser has been demonstrated in the crystals. The slope efficiency up to 43.5% in 0.43% Nd:Sr0.95Y0.05F2.05 was achieved. The system is a promising candidate for highly efficient lasers.

Spectral properties and highly efficient continuous-wave laser operation in Nd-doped Sr(1-x)Y(x)F(2+x) crystals.

High-quality neodymium doped GGG laser crystals have been grown by Czochralski (Cz) method. Results of Nd:GGG thin chip laser operating at 1.064 μm pumped by Ti:sapphire laser operating at 808 nm were reported. The slop efficiency was as high as 20%.

Ti:sapphire laser pumped high average power laser crystal Nd:GGG with high efficiency output

signal incident onto the antenna as for the receiver. Figure 3 shows the measurement setup with the two standard horns 3.0 m away from the antenna. The incident RF signal swept from 5.0 to 6.0 GHz with an output power of 8 dBm. Figure 4 shows the spectrum of the radiating signal from the transmitter. The measured central frequency is 6.002 GHz, only 0.03% deviation from the designed transmitting frequency of 6.0 GHz. Figure 5 gives the IF output of the mixer, recorded by a Tek spectrum analyzer. The IF signal ranges from 250 to 750 MHz, and has a bandwidth of 500 MHz. It corresponds to the RF incident signal sweeping from 5.25 to 5.75 GHz. The IF signal has a maximum response around 500 MHz that corresponds to a receiving resonant frequency of 5.0 GHz, the same as the designed value. IV. CONCLUSIONS A design using one single local oscillator for transmitting and receiving duplex circuitry was presented. A ‘‘proof-of-concept’’ prototype was successfully developed and tested. Although the prototype using a rectangular patch antenna to achieve the LO coupling is shown, other application-specific designs with other types of antennas can be carried out with a similar principle. Such a design is compact, and has potential applications both in short-range communication and millimeter-wave systems.

Yupu Liu

Papers

Passively Q-switched Yb:YAG laser with Cr 4+ :YAG as the saturable absorber

Laser-diode-pumped Cr 4+ ,Nd 3+ :YAG with self-Q-switched laser output of 1.4 W

Spectral properties and highly efficient continuous-wave laser operation in Nd-doped Sr(1-x)Y(x)F(2+x) crystals.

Ti:sapphire laser pumped high average power laser crystal Nd:GGG with high efficiency output

Ti:sapphire laser-pumped self-Q-switched Cr, Nd:YAG laser with single-longitudinal-mode output