Gallium Garnet Crystal Research Articles

Optical rotary power at the resonance of the Terbium 7F 6→ 5D 4 line in Terbium Gallium Garnet

The Tb 3+ absorption line 7F 6→ 5D 4 of the Terbium Gallium Garnet crystal is excited with an Argon ion laser. The Verdet's constant has been determined and reported against 1/ λ 2, showing no significant resonant behaviour at absorption resonance. The utility and the constraints of the crystal at this particular resonant wavelength are pointed out.

磁気冷凍の研究動向

Recent progress in magnetic refrigeration has been reviewed. Adiabatic demagnetization refrigerators (ADR) are under development at NASA for large deployable reflectors and X-ray spectrometers. The refrigerators provide temperatures of 2K at 0.027W for 165s and 0.1K at 0.01W for 13h using gadolinium gallium garnet and paramagnetic salt crystals. The Gas-Gap heat switch is used for the isothermal portion of a Carnot cycle. Active magnetic regenerator (AMR) cycles have the advantage of the Carnot cycle for larger temperature span and refrigeration capacity, in particular, above 20K. A test apparatus of the AMR demonstrated that the refrigeration capacity of 1.5-3.5W was obtainable at the temperature spans of 13-25K with a Carnot efficiency of 42%. Practical applications of magnetic refrigeration are also described.

Continuous lasing at a 2 μm wavelengthin calcium niobium gallium garnet crystals at room temperature

Continuous lasing resulting in the emission of radiation of the 2.02 μm wavelengthwas achieved in Tm3+-activated calcium niobium gallium garnet crystals at room temperature. Lasing was observed when the Tm3+ ions were excited by Nd:YAG laser radiation with λ = 1.06 μm. The output radiation power was 0.02 W. Mechanisms of nonlinear absorption of the pump radiation were investigated.

Proton-induced fluorescence properties of terbium gallium garnet

The authors completed a 3 MeV proton irradiation test on a terbium gallium garnet crystal sample. The main goal was to determine the proton dose required to reduce the fluorescence intensity to half its original value (half-brightness dose) at ambient temperature. The 3 MeV proton half-brightness dose was found to be 1.25 × 1015 p/cm2 using the Birks and Black relation. This decay is comparable to other fluors irradiated by the authors. The sample exhibited a yellow glow when irradiated in a 3 MeV beam. The fluorescence spectrum was composed of four peaks at wavelengths of 487.2 nm, 542.4 nm, 589.92 nm, and 624.1 nm.

Energy transfer in GGG:Yb 3+,Ho 3+ crystals

The energy transfer between Yb 3+ and Ho 3+ ions and the energy migration on Yb 3+ ions as a function of temperature were studied in gadolinium gallium garnet crystals doped with Yb 3+ (5%) and Ho 3+ (3%). It was found that the commonly accepted energy transfer theories do not provide a good description of the system studied. The application of several theories gives contradictory results.

A study of dislocations generated by inclusions in gadolinium gallium garnet crystals by birefringence topography

By means of birefringence topography, the stress fields around and the dislocations generated from iridium inclusions of various shapes in gadolinium gallium garnet (GGG) have been characterized. The Burgers vectors of dislocations have been identified as 1 2 a〈111〉, a〈100〉 and a〈110〉. Some of the dislocations with a〈110〉 Burgers vector are decomposed into two perfect dislocations with 1 2 a〈111〉 Burgers vector. It has been demonstrated that the inclusions acted as effective sources to generate dislocations in GGG crystal during growth and cooling processes.

Energy transfer from tetrahedral Fe3+ sites to Tm3+ in garnets.

A very efficient energy transfer from ${\mathrm{Fe}}^{3+}$ (d tetrahedral sites) to ${\mathrm{Tm}}^{3+}$ (c dodecahedral sites) in yttrium aluminum garnet and gadolinium gallium garnet crystals was observed. The site-selective spectroscopy shows that in case of near-neighbor Fe(d)-Tm pairs the transfer efficiency is 100%. For the other pairs it is less efficient and increases with temperature due to a better superposition of ${\mathrm{Fe}}^{3+}$ emission and $^{3}$${\mathit{H}}_{4}$ ${\mathrm{Tm}}^{3+}$ absorption bands.

Anisotropic effects in the third-harmonic-generation process in cubic crystals

The third-harmonic-generation process is governed by the fourth-rank tensor χ(3), which reflects the crystal symmetry. We use the fundamental output of a Nd:YAG laser as excitation energy to show the anisotropic character of the nonlinear response of a cubic crystal for different samples. A clear dependence of the third-harmonic-generation efficiency on the crystal orientation has been observed in NaF, LiF, Ge, Si, and gadolinium gallium garnet crystals, the last of which has the lowest value of anisotropy among the crystals considered here. The strengths of the anisotropic nonlinear response in Si and Ge are of the same order of magnitude.

Influence of Ce3+ions on the spectroscopic and lasing properties of Y3Al5O12:Ce3+:Er3+and Gd3Ga5O12:Ce3+:Er3+crystals

An investigation was made of the feasibility of sensitizing the luminescence of Er3+ ions by Ce3+ ions in YAG and gadolinium gallium garnet (GGG) crystals. Efficient nonradiative transfer of energy from Ce to Er was observed in the YAG matrix. No sensitization was observed in a GGG:Er:Ce crystal. Flashlamp pumping of a YAG:Er:Ce crystal (λ = 2.94 μm) yielded a free-running threshold of 52 J and a differential efficiency of 2.1%. Coactivation of GGG:Er crystals with Ce3+ ions can extend the pump spectrum into the ultraviolet and enhance the lasing efficiency.

PassiveQswitching of pulsed Nd3+lasers using YSGG:Cr4+crystal switches exhibiting phototropic properties

An experimental investigation was made of multispike lasing regimes in various pulsed Nd3+ lasers Q-switched using a movable passive switch based on an yttrium scandium gallium garnet crystal containing Cr4+ ions. The results indicate that these passive switches should make it possible to develop Nd3+ lasers with high average and peak powers.

Spectroscopic and lasing properties of calcium niobium gallium garnet activated with Tm3+and Cr3+ions

An investigation was made of spectroscopic and lasing properties of a calcium niobium gallium garnet crystal (CNGG) activated with Tm and Cr. A study was made of the kinetics of decay of the luminescence emitted by the Cr3+ ions. Efficient nonradiative transfer of energy from the Cr3+ to the Tm3+ ions was observed at room temperature. Stimulated radiation was generated in CNGG:Tm:Cr crystals (due to the 3F4→3H6 transition) under conditions of free running: the wavelength of this radiation was 2.02 μm at room temperature.

Efficient laser with a rectangular active element

A solid-state laser with a rectangular active element was constructed. When this element was a neodymium-activated gadolinium gallium garnet crystal and the laser was operated under conditions ensuring a high average power, the output power was 180 W at a pulse repetition frequency of 25 Hz and the absolute efficiency was ~ 3%. The divergence of the output radiation did not exceed 10 mrad and the specific output power was 7.5 W/cm3.

Thermal effects on cavity stability of chromium- and neodymium-doped gadolinium scandium gallium garnet laser under solar-simulator pumping

A chromium- and neodymium-codoped gadolinium scandium gallium garnet (Cr:Nd:GSGG) crystal was tested for pulsed- and continuous-wave (cw) laser operations with a flashlamp and solar simulator as pumping sources. The crystal has been considered as a good candidate for a solar-pumped laser because of its broad absorption bands over the solar spectrum. However, it was observed experimentally and theoretically that its cw laser operation is difficult at high pump powers because too many thermal lensing effects are induced. Only at low solar-simulator beam intensities of up to 1500 solar constants (203 W/cm2 ) was cw laser operation lasting longer than 10 min achieved. For higher pump beam intensities of up to 2500 solar constants (338 W/cm2 ), a quasi-cw-laser operation was obtained with continuously chopped pumping with a duty cycle of 0.5 and a repetition rate of 13 Hz. The experimental result was compared with the calculated stability condition of the laser resonator for various pump powers and showed that the thermal focusing of the Cr:Nd:GSGG is 15–8 times greater than that of the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for the pump beam intensities from 1000 to 3000 solar constants.

Optical properties of color centers in calcium-stabilized gadolinium gallium garnets.

The addition of small amounts of calcium during the crystal growth of large-diameter, gadolinium gallium garnet (GGG) crystals creates color centers that absorb in the near-uv region of the spectrum. Ultraviolet and \ensuremath{\gamma}-ray irradiation of the crystals produced changes in the intensities of the uv color-center bands along with a broad absorption throughout the visible spectrum. The color center that gives rise to an absorption band at 350 nm serves as a photoionizable donor center so that uv excitation results in a visible coloration of the crystals. The effects of oxidation and reduction treatments on the strength of the color-center bands and on the radiation response of the material were examined. Photoluminescence bands were observed in both reduced GGG crystals as well as crystals that were irradiated with neutrons. Visible coloration is likely to occur during flashlamp pumping of laser rods that utilize large-diameter GGG crystals as the laser host. The changes in the optical properties of the material under uv excitation indicate that the addition of small amounts of calcium to assist in the growth of large-diameter crystals is likely to result in the degradation of laser performance.

Calcium lithium niobium gallium garnet crystals activated with Cr3+, Tm3+, and Ho3+ions as a new active medium for λ ≈ 2 μm lasers

An investigation was made of the luminescence and lasing spectra of a calcium lithium niobium gallium garnet crystal activated with chromium, thulium, and holmium ions. Kinetics of decay of the Cr3+ luminescence was investigated and it was concluded that energy transfer from the Cr3+ to the Tm3+ ions was efficient. An investigation was made of the lasing characteristics of this crystal (λl = 2.09 μm) under free-running conditions at room temperature.

Lasing of a calcium niobium gallium garnet crystal activated with chromium and erbium (λ = 2.71 μm)

An investigation was made of the luminescence spectra and lasing parameters of a calcium niobium gallium garnet crystal activated with chromium and erbium. The lifetimes of the upper 4I11/2 and lower 4I13/2 active levels of the Er3+ ions were determined. The lasing parameters of the crystal (λlas = 2.71 μm) were determined under free-running conditions at room temperature.

Calcium lithium niobium gallium garnet crystals activated with Er3and Cr3+as a new active medium for 3-μ lasers

An investigation was made of the luminescence spectra and lasing properties of a calcium lithium niobium gallium garnet crystal activated with chromium and erbium. The lifetimes of the upper (4I11/2) and lower (4I13/2) active levels of the Er3+ ion were determined. A study was made of the kinetics of decay of the Cr3+ luminescence and it was concluded that energy was transferred from the Cr3+ to the Er3+ ions. Lasing properties of the crystal (λl = 2.707 μm) were studied under free-running conditions at room temperature.

Generation of a giant pulse in the TEM00mode (λ = 2.088 μm) in a flashlamp-pumped YSGG:Cr:Tm:Ho crystal

Q-switching in a flashlamp-pumped yttrium scandium gallium garnet crystal, activated with chromium, thulium, and holmium ions (YSGG:Cr:Tm:Ho), resulted in emission of the TEM00 mode because of the 5I7→5I8 transition in Ho ions (λ = 2.088 μm) at room temperature. When the pump energy was 80 J and the repetition frequency was 1 Hz, a giant TEM00 pulse with an energy of 50 mJ was generated.

Yttrium scandium gallium garnet laser with a waveguide element activated with Cr3+and Nd3+

A description is given of a waveguide active element made from an optically dense medium in the form of an yttrium scandium gallium garnet crystal activated with chromium and neodymium. A solid-state laser utilizing this active element emitted an average power of approximately 70 W with a divergence of 8' at a pump pulse repetition frequency of up to 35 Hz and an absolute lasing efficiency of 1.7%. An absolute lasing efficiency of 2.5% was obtained in the single-pulse regime using an illumination enclosure specially designed for a plate made of an optically dense active medium.

Laser utilizing gadolinium scandium aluminum garnet activated with chromium and neodymium

A pulse-periodic laser has been developed utilizing a new active medium, a gadolinium scandium aluminum garnet crystal activated with chromium and neodymium. An absolute free-running efficiency of 3.4% with a differential efficiency of 4.4% was obtained in the single-pulse regime. Thermooptic effects in the new active medium were approximately 1.5 times weaker than those in scandium gallium garnet crystals. The damage threshold for cylindrical active elements with a mat surface was approximately 500 W per centimeter of the active element.