GSAG Crystal Research Articles

Efficient continuous-wave and passively Q-switched Nd:GSAG laser operating at 1.3 μm

We report on the laser performance of neodymium-doped gadolinium scandium aluminum garnet (Nd:GSAG) crystals at 1.3 μm for the first time, to the best of our knowledge. An efficient continuous-wave (CW) laser at 1336 nm and on output power of up to 2.01 W was obtained under an absorbed pump power of 4.89 W with slope and optical-to-optical efficiencies of 43.4 % and 41.1 %, respectively. Furthermore, a passively Q-switched (PQS) laser with a Co:MgAl2O4 crystal serving as a saturable absorber in a compact plano-plano resonator cavity was examined. A maximum average output power of 0.2 W was obtained with a pulse width, pulse energy, and peak power of 34.4 ns, 22.2 µJ, and 645 W, respectively. Our results indicated that Nd:GSAG crystals are promising for producing high-efficiency CW lasers and effective PQS lasers at 1336 nm.

Optical temperature sensing of Yb,Er:GSAG single crystal in both upconversion and downconversion dual-mode luminescence

Fluorescence intensity ratio thermometry represents a novel non-contact approach for rapid and precise temperature measurements. In this study, a Yb,Er co-doped Gd3Sc2Al3O12 single crystal (Yb,Er:GSAG) was investigated, exploiting the dual-mode luminescence of upconversion and downconversion for optical temperature sensing applications. The crystal exhibited distinct luminescence behaviors when subjected to 266 nm, 355 nm, and 980 nm laser excitations, manifesting a dark blue appearance under 266 nm ultraviolet (UV) excitation and a green hue under 355 nm and 980 nm excitations. Specifically, under 355 nm excitation, the crystal demonstrated a predominantly pure green upconversion, with a green-to-red ratio of 38. For the first time, we propose an investigation into the temperature sensing behavior under dual-mode luminescence in the same crystal, utilizing the fluorescence intensity ratio of the 2H11/2 and 4S3/2 thermally coupled energy levels of Er3+. The obtained maximum relative sensitivities (SR) for the two fitted luminescence modes were found to be 101.80×10−4 K−1 at 300 K (980 nm excitation) and 126.39×10−4 K−1 at 300 K (355 nm excitation), respectively. The impressive SR values substantiate Yb,Er:GSAG crystal as highly promising candidates for optical temperature sensing applications.

Growth, structure and upconversion properties of Yb3+ and Er3+ co-doped Gd3Sc2Al3O12 crystal

Upconversion luminescent materials exhibit excellent near-infrared to visible conversion properties that make them crucial for optoelectronics, visible display devices, and biological labels. Herein, we report a high-quality Yb3+ and Er3+ co-doped Gd3Sc2Al3O12(GSAG) single crystal which was grown successfully by the traditional Czochralski method with Er3+ and Yb3+ doping concentration of 1 at.% and 10 at.%, respectively. The structure parameters of the crystal were observed by the X-ray Rietveld refinement method. In addition, the transmission and upconversion emission properties of the crystal were analyzed at room temperature. The 940 nm excited upconversion energy transfer mechanism and dependence of the green-to-red upconversion intensity ratio (Ig/r) on pump power were investigated. A dominant two-photon absorption process of the green and red upconversion emission bands were revealed in Yb,Er:GSAG crystal. The results indicate the crystal is a promising upconversion single crystalline material.

Diode end-pumped dual-wavelength Er,Pr:GSAG laser operating at 2696 and 2828 nm

We demonstrated the 962 nm laser diode end-pumped Er3+, Pr3+ co-doped GSAG laser operated in dual-wavelength of 2696 and 2828 nm. The absorption and fluorescence spectra of Er,Pr:GSAG crystal were investigated to determine the potential of laser generation in mid-infrared wavelength regions. The lifetimes of Er3+ in GSAG crystal for the upper laser level 4I11/2 and lower level 4I13/2 are 0.18 and 0.47 ms, respectively, for co-doped Pr3+ ion. The maximum average output power of 344 mW is achieved. In addition, a series of investigations for Er,Pr:GSAG laser performance were launched on the pump pulse width, repetition frequency and resonant cavity length. The results indicate that the small pump pulse width and low repetition frequency are beneficial to decrease the thermal lensing effect and improve the laser efficiency and beam quality.

Growth, spectroscopic, diode-pumped mid-infrared laser properties of Er:GSAG crystal

A great potential mid-infrared laser crystal of heavily Er3+ doped GSAG crystal with high optical quality is successfully grown by Cz method. The crystal quality of Er:GSAG crystal is determined by XRC. The structure parameters of Er:GSAG crystal are obtained by the X-ray Rietveld refinement method (a = b = c = 12.3196 Å). The absorption cross section at 961 nm and 967 nm are 0.381 × 10−21 cm2 and 0.414 × 10−21 cm2, respectively. The 962 nm laser diode end-pumped Er:GSAG laser operated at 2828 nm is demonstrated for the first time. The performance of Er:GSAG laser is investigated in great detail. A maximum output power of Er:GSAG laser is 410 mW when pumped by 962 nm LD at 300 Hz and 0.5 ms. Simulating results display the highest temperatures of Er:GSAG laser spot is 345.8 K, indicating a small thermal lensing effect of Er:GSAG crystal. Besides, the laser performance of Er:GSAG crystals which irradiate by different doses of gamma-ray are used to investigated its potential for working in the radiation resistance environment. The results show the relatively minor differences on the Er:GSAG lasers performance, indicating a great potential of Er:GSAG crystal in radiant environment application.

A promising high-efficient radiation resistant laser crystal Nd:GSAG

In this study, the effect of gamma-ray irradiation on the spectral and laser properties of Nd:GSAG crystal is investigated. With 20 Mrad gamma-ray irradiation, the crystal’s absorption at around 808 nm and emission at 1060 nm are only affected slightly. In addition, the lifetime of the 4F3/2 → 4I11/2 transition becomes longer when increasing the irradiation doses. All these optical properties changes after the irradiation could be attributed to the formation of F+-centers in the crystal. Using LD pumping, high-efficient 1.06 μm continuous-wave laser operation was realized in the crystal. It is worthy to note that the laser efficiency is influenced slightly by the gamma-ray irradiation, which suggest that Nd:GSAG crystal can be considered as a potential efficient laser gain medium for being used in radiant environment.

Effects of the gamma-ray irradiation on the structure, spectral and laser damage threshold of Nd:GSAG crystal

Nd:GSAG crystal was irradiated by 60Co gamma-ray with the irradiation doses of 0, 2, 10 and 20 Mrad, respectively, to investigate its radiation resistant properties. XRD and Raman spectra characterization results indicate that the crystal structure was unchanged by the irradiation. Therefore, the color change of the crystal caused by irradiation could be attributed to the formation of the color centers inside the crystal. Only slightly decreased of the transmittance and laser damage threshold of the crystal with the irradiation dose of 20 Mrad indicate the crystal is of excellent radiation resistant ability. All the results suggest that Nd:GSAG crystal can be considered as a potential laser gain medium for being used in radiant environment.

Enhanced radiation resistant properties of Nd:GSAG laser crystal by co-doping of Cr3+

With the further exploration of outer space by human beings, the demand for outer space laser is increasing. Therefore, developing laser materials that can resist the space irradiation become increasingly important. In this study, high quality Nd, Cr:GSAG crystal was grown successfully by Czochralski method. The X-ray diffraction results indicate that the crystal structure remains unchanged after the irradiation with 60Co gamma-ray. In addition, Raman, absorption and fluorescence spectra of the as-grown crystal are almost unaffected by the irradiation, suggesting the excellent radiation resistant ability of the crystal. Compared with the Nd:GSAG crystal, the co-doping of Cr3+ can enhance the radiation resistant ability and luminescent efficiency apparently. Importantly, LD pumped 1.06 μm laser results indicate the Nd, Cr:GSAG crystal can be considered as a promising high efficiency laser material for the application in harsh radiation environment, such as in outer space.

Growth, defects, radiation resistant and optical properties of 30 at% Er:GSAG laser crystal

30 at% Er3+:GSAG single crystal was successfully grown by the Czochralski method. The dislocation of (111) face is studied using the chemical etching with the phosphoric acid etchant. The luminescence properties at 2.6–3.0 µm are systematically studied by measuring the fluorescence spectra and lifetimes to the transition of 4I11/2 → 4I13/2. The long fluorescence lifetime, high fluorescence intensity, and large gain σem spectra indicate that the 30 at% Er:GSAG crystal has the great potential for the multi-wavelength laser output at 2.6–3.0 µm. Meanwhile, the absorption and fluorescence properties of 30 at% Er:GSAG crystal under the gamma-ray radiation with three different intensities (35, 70, and 105 Mrad) have been investigated, indicate that this crystal can be considered as a promising MIR laser gain medium for being used under radiant environment. In addition, the luminescence property of 30 at% Er:GSAG crystal in visible and 1.5–1.7 µm was also studied, which shows the possibility to generate the laser around 1.6 µm.

Growth, structure and radiation resistant properties of Er,Pr:GSAG laser crystals

Er, Pr co-doped GSAG laser crystal with high optical quality was successfully grown by the Czochralski method for the first time. X-ray rocking curve exhibit the high crystalline quality of this crystal. The intensities of optical transmission and luminescence of Er,Pr:GSAG crystal were not deteriorate after the gamma-ray irradiation even with a dose of 1.16 × 106 Gy, confirming the excellence radiation resistant property of Er, Pr:GSAG crystals. The efficiencies of energy transfer from 4I11/2 to 1G4 and 4I13/2 to 3F4 between Er3+ and Pr3+ ions in GSAG crystal are determined as 16.7% and 94.9%, which indicate that the Pr3+ can act as an deactivator ions for Er3+ ions in Er,Pr:GSAG crystal. Additionally, the luminescence spectra of Er,Pr:GSAG crystal are compared with that of Er:GSAG crystal in the visible and near-IR regions, which provided that Pr3+ ions can efficiently depopulate the 4I13/2 level and reduce the fluorescence lifetime. All the results demonstrate that Er,Pr:GSAG crystal can realize multi-wavelength laser output at 2.6–2.9 μm under harsh radiation environment.

Czochralski growth and spectral investigations of Er:GSAG laser crystal

Er3+ doped GSAG laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. The structural parameters and the high crystalline quality of this crystal were determined. Judd-ofelt (J-O) parameterization scheme was applied to analyze the absorption spectra at room temperature. Accordingly, the lines strengths, oscillator strengths, transition probabilities, fluorescence branching ratios, and radiative lifetimes were calculated to characterize the laser properties of Er:GSAG crystal. Additionally, the fluorescence spectra and lifetimes of Er:GSAG crystal were measured and studied. The stimulated emission cross-section spectra and gain cross-section spectra were evaluated for 4I13/2 →4I15/2 (1.5–1.6 µm) transitions which indicate high potential of 1 at% Er:GSAG for laser emissions at 1567 and 1605 nm. Furthermore, the possibility of Er:GSAG crystal to realize the visible laser output pumped by the GaN LDs were initially studied and analyzed.

Effective segregation during Czochralski growth and spectral properties of Nd3+ in GSAG crystal

GSAG and Nd:GSAG crystals were grown by standard Czochralski technique. The refractive index of GSAG in the wavelength range 500–3000nm, effective segregation coefficient and absorption cross sections of Nd3+ in GSAG were determined by optical absorption method. The effective segregation coefficient was calculated to be 0.525. The spectroscopic and laser properties of Nd:GSAG crystal were studied by Judd–Ofelt analysis. The Judd–Ofelt parameters were calculated to be Ω2=1.32×10−21cm2, Ω4=2.93×10−20cm2 and Ω6=3.91×10−20cm2. With these intensity parameters, the values of absorption and emission oscillator strengths, transition probabilities, fluorescence ratios and radiative lifetimes were obtained. The large fluorescence ratio of |[4F]3/2〉 is very favorable for laser operation at 942nm. These results confirm that Nd:GSAG is a suitable laser material for water vapor detection by DIAL.

Electronic structure and bonding in garnet crystalsGd3Sc2Ga3O12,Gd3Sc2Al3O12,andGd3Ga3O12compared toY3Al3O12

The electronic structure and bonding of ${\mathrm{Gd}}_{3}{\mathrm{Sc}}_{2}{\mathrm{Ga}}_{3}{\mathrm{O}}_{12}$ (GSGG), ${\mathrm{Gd}}_{3}{\mathrm{Sc}}_{2}{\mathrm{Al}}_{3}{\mathrm{O}}_{12}$ (GSAG), and ${\mathrm{Gd}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$ (GGG) crystals with a garnet structure are studied by means of first-principles local-density calculations. The results are compared with a similar calculation on yttrium aluminum garnet [${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ (YAG)]. The calculated equilibrium volumes of the three crystals are close to the measured volumes with a slight overestimation for GGG. GGG also has a smaller bulk modulus than the other three crystals. The calculated density of states and their atomic and orbital decompositions are presented and contrasted. All four crystals show very similar band structures and interatomic bonding. However, it is found that in GSGG and GSAG crystals, the Sc atom at the octahedral site shows a higher covalent character and an increased bond order in comparison to Ga or Al at the same site. This result may provide some insight into the significant difference in the radiation hardness of ${\mathrm{Cr}}^{3+}{:\mathrm{N}\mathrm{d}}^{3+}:\mathrm{G}\mathrm{S}\mathrm{G}\mathrm{G}$ as compared to ${\mathrm{Nd}}^{3+}:\mathrm{Y}\mathrm{A}\mathrm{G}.$

Cr-Tm and Cr-Er energy transfer in GSAG and YSGG crystals

Cr-Tm and Cr-Er energy transfer in GSAG and YSGG crystals