Takagimi Yanagitani

Neodymium doped yttrium aluminum garnet (Y3Al5O12) nanocrystalline ceramics—a new generation of solid state laser and optical materials

We have developed and adequately characterized a new generation of solid-state laser and optical materials on the basis of highly transparent nanocrystalline yttrium aluminium garnet Y3Al5O12 (YAG) ceramics. We consider this new type of inorganic laser media as an illustration of selected results of the latest investigations of laser and spectroscopic parameters of nanocrystalline Nd3+:YAG ceramics. In particular, absorption, luminescence, stimulated Raman scattering properties, as well as highly efficient CW laser oscillation at wavelength of 1064 nm under laser-diode pumping were investigated. The results show that this new laser material is a very good alternative to Nd3+:YAG single crystals. In particular, in preliminary comparison laser experiments with both Nd3+:YAG ceramic and single-crystal rods, output powers of 88 W and 99 W were obtained corresponding to optical-to-optical efficiencies of 30% and 34% for ceramic and single crystal rods, respectively. A CW 1.46 kW high power Nd:YAG ceramic laser was developed. Quite recently, laser oscillation at ≈1.32 μm was also demonstrated.

Nd3+:Y2O3 Ceramic Laser

We have demonstrated CW one-micron laser oscillation in new ceramic laser material on the base of cubic Nd3+:Y2O3. Slope efficiency of 32% was achieved on an uncoated 1.5 at.% Nd3+:Y2O3 ceramic plate with size of 14 ×2.7 mm under laser diode end-pumping.

Induced emission cross section of Nd:Y3Al5O12 ceramics

Optical absorption and emission spectra have been measured for Nd‐doped Y3Al5O12 ceramics obtained by a urea precipitation method. The optical properties of the ceramics are almost the same as those of single crystals grown by the Czochralski method and floating‐zone method, except for a higher background absorption of 2.5–3 cm−1. The energy‐level structure for Nd3+ in the Y3Al5O12 ceramics is determined for a 1‐at. % Nd concentration. The induced emission cross section for the 1‐at. %‐Nd‐doped ceramic is calculated to be 4.9×10−19 cm2, which falls in the range reported for the Nd:Y3Al5O12 single crystals. The Nd concentration dependence of the emission decay time at the 1064‐nm laser wavelength was also measured, and typical concentration quenching was observed. The decay time of the 1‐at. %‐Nd‐doped ceramic is 219 μs, which is slightly smaller than the reported values for single crystals.

Spectroscopic and stimulated emission Characteristics of Nd/sup 3+/ in transparent YAG ceramics

Nd: YAG ceramic materials have been synthesized using vacuum sintering technique with the raw materials prepared by the nano-crystalline methods. The spectroscopic studies suggest overall improvement in absorption and emission and reduction in scattering loss. Judd-Ofelt analysis has been employed to compute the relevant spectroscopic and radiative parameters of the material. The SEM and TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. Fluorescence and Raman measurements reveal that the Nd/sup 3+/-doped YAG ceramic is almost equivalent to its single-crystal counterpart in its radiative and nonradiative properties. Individual Stark levels for /sup 2s+1/L/sub J/ manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd: YAG ceramic. Laser performance studies favor the use of high-concentration Nd: YAG ceramics in the design of an efficient microchip laser. With 4 at% Nd: YAG ceramic acting as a microchip laser, we obtained a slope efficiency of 40%. High-power laser experiments yield an optical-to-optical conversion efficiency of 30% for Nd (0.6 at%):YAG ceramic as compared to 34% for an Nd (0.6 at%):YAG single crystal. The oscillation experiments at 1.3 mm gives a slope efficiency of 35%. Optical gain measurements conducted in these materials also show values comparable to single crystal, supporting that these materials could be suitable substitutes to single crystals in solid-state laser applications.

Yb3+:Y2O3 Ceramics – a Novel Solid-State Laser Material

A new solid-state laser based on Yb3+-doped highly transparent nanocrystalline yttria (Y2O3) ceramics was developed. At room temperature and under a pump power of 2.63 W from a single InGaAs laser diode at ≈ 0.94 µm, a continuous-wave laser output of 0.47 W at 1.077 µm wavelength was obtained corresponding to a slope efficiency of about 32%. Some main spectroscopic properties of Yb3+:Y2O3 ceramics were also investigated.

OPTICAL SPECTRA OF UNDOPED AND RARE-EARTH-( = PR, ND, EU, AND ER) DOPED TRANSPARENT CERAMIC Y3AL5O12

Undoped and rare‐earth‐ (Pr, Nd, Eu, and Er) doped transparent Y3Al5O12ceramics have been prepared, and their optical spectra have been measured. It is found that absorption coefficient of the undoped ceramic Y3Al5O12 is almost independent of wavelength with 0.258 cm−1, which gives transmittance of the undoped ceramic Y3Al5O12 to be, for example, 95% for a 2‐mm height. Peaks in the absorption and emission spectra of Pr:Y3Al5O12 are assigned to the transitions in 4f 2 configuration. The transitions from the multiplets with total angular momentumJ=0 to multiplets with even J momentum are strong as predicted by Judd–Ofelt theory. The overall and detail structure of the absorption and emission spectra of Nd:Y3Al5O12 is the same as those in a previous publication. However, the absorption coefficient at nonabsorbing wavelengths by Nd3+ is reduced from more than 1.7 to 0.25 cm−1. A simple estimation of the population inversion threshold of the Nd:Y3Al5O12ceramic reveals that the threshold is still about 25 times larger than that of single‐crystal Nd:Y3Al5O12. Peaks in the absorption and emission spectra of Er:Y3Al5O12ceramic are assigned to the transitions in 4f 11 configuration. The transition energies agree well with those reported for single‐crystal Er:Y3Al5O12 and the other hosts within 30 cm−1. A Stark splitting scheme for some multiplets has been constructed. Peaks in the emission, absorption, and excitation spectra of Eu:Y3Al5O12ceramic are assigned to the transitions in 4f 6 configuration. The transition energies are in very good agreement with those of single‐crystal Eu:Y3Al5O12 within 8 cm−1 for the emission peaks and 3 cm−1 for the absorption and excitation peaks. Spectralcharacteristics and derivation of a broad peak in the absorptionspectrum at around 280 nm are discussed in some detail.

Cryogenic temperature characteristics of Verdet constant on terbium gallium garnet ceramics

As the first demonstration of Faraday effect in a TGG ceramics, its Verdet constant at 1053 nm is evaluated to be 36.4 rad/Tm at room temperature which is same as that of the single crystal. In addition, the temperature dependence of Verdet constant is obtained experimentally. At liquid helium temperature, it is 87 times greater than that at room temperature.

Highly efficient continuous-wave operation at 1030 and 1075 nm wavelengths of LD-pumped Yb3+:Y2O3 ceramic lasers

Room-temperature cw laser oscillations at 1030 and 1075 nm wavelengths were demonstrated for the TEM00 mode with Yb3+:Y2O3 ceramics by LD-pumping. A maximum extraction efficiency of 72% at 1075 nm lasing wavelengths and of 45% at 1030 nm lasing wavelengths were observed.

Laser-diode pumped heavy-doped Yb : YAG ceramic lasers

Laser performance of heavy-doped Yb:YAG ceramics was investigated using a two-pass pumping miniature laser configuration. Slope efficiency of 52% and optical-to-optical efficiency of 48% have been achieved for 1-mm-thick YAG ceramic doped with 20 at.% ytterbium ions. Laser spectra of Yb:YAG ceramic and single-crystal lasers were addressed under different intracavity laser intensities. Heavy-doped Yb:YAG ceramic is more suitable for a thin disk laser than a single-crystal with the same Yb(3+)-ion lasants.

Composite Yb:YAG/Cr(4+):YAG ceramics picosecond microchip lasers.

Efficient laser-diode pumped picosecond self-Q-switched all-ceramic composite Yb:YAG/Cr(4+):YAG microchip lasers with 0.72 MW peak power has been developed. Lasers with nearly diffraction-limited beam quality (M(2) < 1.09), oscillate at stable single- and multi- longitudinal-modes due to the combined etalon effects in the Yb:YAG and Cr(4+):YAG parts of its binary structure.