Garnet Laser Crystals Research Articles

Diode End-Pumped 1.37 W Er:YSGG Continuous-Wave Laser Around 2.8-μm

We demonstrate the laser performance of a LD end-pumped Er:YSGG crystals with different doping concentrations comparatively. The experimental results show that 30 at. % Er:YSGG crystal with dimensions of 2 mm ×2 mm ×8 mm has the best laser output. In continuous-wave (CW) mode and pulse mode, the maximum output powers of 1.37 and 1.20 W are achieved, corresponding to slope efficiencies of 23.62% and 22.91%, respectively. To the best of our knowledge, compared with other Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped garnet laser crystals, we obtained a larger power and higher efficiency CW laser simultaneously for LD end-pumped Er:YSGG crystal. The beam quality factor M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in x and y directions are determined to be 1.64/1.65, suggesting the Er:YSGG laser possesses a higher beam quality. All these results indicate that Er:YSGG is a promising mid-infrared gain medium for high efficiency and high power laser operation.

Thermal conductivity of synthetic garnet laser crystals

The thermal conductivities of nine different synthetic garnet laser crystals at various temperatures, range from 273 to 393 K have been investigated by instantaneous measurement method. The results show that the thermal conductivity of each crystal decreases exponentially with the temperature increasing. It is notable that, different host crystals, such as YAG, GGG, and GSGG have different thermal conductivity, which is attributed to the crucial influence of crystal structure and composition on the absolute value of their thermal conductivity. Moreover, with respect to the same host crystals, the impurity scattering also results in the change of their thermal conductivities. This is because that a higher concentration of doped ions leads to a more phonon scattering modes, which results in a shorter mean free path of the phonons and a lower thermal conductivity. In addition, different host crystals have various dependences of thermal conductivity on dopant concentration. This works provides reliable and useful information for designing high power, high quality, and high stability laser devices.

Influence of probe beam multi-reflection on thermal lens measurements: Application to Nd:YAG rods

In this work time resolved thermal lens measurements were carried out in Nd-doped yttrium aluminum garnet laser crystal. We observed that due to the probe beam multi-reflection the thermal lens signal was influenced by the moving fringes that occurred in front of the detector. By using a heat sink device, this effect was minimized permitting the determination of the temperature coefficient of optical path length, the thermal diffusivity and the thermal conductivity of the sample. As a complementary technique, the thermal relaxation method was used to measure the sample specific heat.

Time-resolved thermal lens determination of the thermo-optical coefficients in Nd-doped yttrium aluminum garnet as a function of temperature

In this work, time-resolved thermal lens measurements are carried out in Nd-doped yttrium aluminum garnet laser crystal as a function of temperature. The temperature coefficient of the optical path length, the thermal diffusivity, and the thermal conductivity were determined in the temperature range between 22°C and 180°C. In addition, the specific heat was measured by the thermal relaxation method in the same temperature range. The results showed that the thermal conductivity and the temperature coefficient of the optical path length are responsible for the strong increase of the thermal lens amplitude when the sample temperature was increased. These results suggest that the time resolved procedure is useful in the study of laser materials and may be an important tool for laser designers.

Site-selective study of Nd3+ optical centers in Ca3Sc2Ge3O12 laser garnet crystals

The Nd3+ multicenter distribution in a Ca3Sc2Ge3O12 garnet laser crystal has been analyzed by low temperature site-selective laser spectroscopy. Two nonequivalent Nd3+ centers have been identified and characterized in this host lattice. The effect of codoping the crystal with MgO on the Nd3+ center distribution has also been investigated, since this codoping enables considerable enhancement of the doping levels of these crystals. Three different centers were observed in the codoped crystals, together with a reduction of inhomogeneous emission broadening. The nature of the optical centers present in both cases is discussed by considering the charge compensation mechanisms involved in accommodation of Nd3+ ions.

Radiative and non-radiative energy transfers in Yb3+-doped sesquioxide and garnet laser crystals from a combinatorial approach based on gradient concentration fibers

The laser heated pedestal growth (LHPG) method allows us to grow Yb3+-doped oxide single crystal fiber with no Yb segregation. We have choosen Y3Al5O12 (YAG) Yttrium aluminum garnet and Y2O3 yttria sesquioxide as Yb3+-doped host crystals, which are considered to be among the best laser crystals due to unusual combination of favorable properties. A combinatorial chemistry approach has been applied by growing concentration gradient crystal fibers allowing the study of the excited state dynamics by the measurement of two important features in laser crystals: the intrinsic radiative lifetime and the analysis of radiative and non-radiative energy transfers which occur in the Yb3+ concentration quenching processes.

Q-switching in a Cr3+:Yb3+:Ho3+:YSGG crystal laser based on the 5I6 — 5I7 (λ=2.92μm) transition

An investigation was made of the generation of giant pulses in a new yttrium scandium gallium garnet laser crystal doped with holmium (Cr3+:Yb3+:Ho3+:YSGG) operating on the basis of the self-terminating 5I6 — 5I7 transition. Q-switching was performed by an electro-optical lithium niobate switch, a passive switch based on an epitaxial film of indium arsenide on a gallium arsenide substrate, or a passive switch consisting of water. The 2.92 μm wavelength dominated giant pulse generation, whereas under free-running conditions the radiation was discretely tunable in the range 2.84 —3.05 μm. Depending on the Q-switching method, pulses of 60 — 160 ns duration were generated and the pulse energy was ∼20 mJ. The second and fourth harmonics of the holmium laser radiation were generated and the efficiency of each frequency-multiplication stage was ∼20%.

Characterization of garnet laser crystals by cathodoluminescence emission in a scanning electron microscope

Samples of varying optical quality cut from Czochralski-grown Nd 3+:YAG and Cr 3+:Tm 3+:YAG single crystals have been investigated using standard cathodoluminescence accessories in a scanning electron microscope. The cathodoluminescence emission reveals, with good resolution, a large variety of defects and non-uniformities such as growth striations, facets, inclusions. The formation of facets shows very clearly many details about the coring of the crystal. Core formation and growth striations are discussed in connection with the crystal growth technology.

Growth and investigation of substituted gadolinium gallium garnet laser crystals

Gadolinium gallium garnets substituted with (Ca,Zr), (Mg,Zr) and (Ca,Mg,Zr) are considered to be potential new laser materials. Such substituted GGG boules double-doped with (Nd,Cr) and single-doped with Cr have been grown by the Czochralski method. Color center investigation and lattice constant determination have been carried out. Laser output slope efficiency for a GGG(Ca,Mg,Zr) : (Nd,Cr) rod of dimensions 5 mm diameter by 40 mm long is greater than 0.7%.

The effect of the crystal field strength on the optical spectra of Cr3+ in gallium garnet laser crystals

We have investigated the basic spectroscopic properties of Cr3+-doped gallium garnets. Weak crystal fields (Dq/B=2.39–2.55) lead to broad4 T 2→4 A 2 fluorescence in the 700–950 nm range depending on the chemical composition of the crystals. At room temperature the4 T 2→4 A 2 transition is homogeneously broadened, whereas the 4 K spectra of the2 E→4 A 2 transition show inequivalent Cr3+ sites and inhomogeneous linewidths of 8 cm−1 in these laser crystals. From 300 to 4 K, the oscillator strength of the4 T 2→4 A 2 transition is reduced by a factor of about 0.6 due to the temperature dependent electron phonon coupling. The transition probability of the2 E→4 A 2 transition correlates with the energetic position of the4 T 2 level, which is admixed into the2 E level via spin-orbit coupling. The comparison of the2 E→4 A 2 phonon sideband structure in garnets of different chemical compositions allows the assignment of some peaks to GaO4-tetrahedron modes of the garnet structure.

A possible contribution to light loss in calcium tungstate and yttrium aluminium garnet laser crystals by scattering

Laser measurements have shown that calcium tungstate CaWO4 and yttrium aluminium garnet Y3Al5O12 (YAG) crystals have optical loss coefficients in the region of 1·0 and 0·3% cm−1 respectively. One of the possible mechanisms to explain at least part of this loss would be scattering from centres within the material. Centres which might act in this way have been observed by electron microscopy, and have diameters ranging from 500-5000 Å. In this note we calculate the ratio m of the refractive index of the bulk lattice to that of the particles, such that the experimentally observed loss would be produced. It is found that the deviation of m from unity need be only very small. The possible composition of the particles is discussed in the light of this result.