Search

Electronic structure, optical dispersion and luminescence properties of terbium gallium garnet (Tb3Ga5O12, TGG) were investigated.

We report on a 928 nm laser based on quasi-three-level transition of 4F3/2 → 4I9/2 in a Nd:Gd0.69Y0.3TaO4 mixed single crystal. With LD pumping at 808 nm, an output energy of 29.8 mJ at 928 nm is achieved with an optical-to-optical efficiency of 16.5% and a slope efficiency of 21.2%. In comparison, using 879 nm LD pumping, the maximum output energy at 928 nm reaches 48.5 mJ with an optical-to-optical efficiency of 33.4% and a slope efficiency of 38.0%.

A promising 2.9 µm Ho:GdYTaO4 laser crystal was grown successfully by the Czochralski method for the first time. The crystal belongs to the monoclinic space group of I2/a (No. 15) and high crystalline quality is demonstrated by X-ray rocking curves. The spectral properties of Ho:GdYTaO4 crystal at room temperature are investigated. Based on the Judd–Ofelt theory, the intensity parameters, spontaneous transition probabilities, fluorescence branching ratios, and radiative lifetimes are obtained in detail. The strongest emission peak is located at 2848 nm, and the full width at half maximum is about 15 nm. The experimental lifetimes of 5I6 and 5I7 levels are 0.31 and 8.08 ms, respectively. Moreover, the Stark levels of 5I6, 5I7, and 5I8 are identified and the splitting values are calculated to be 254.1, 226.7, and 370. 4 cm−1, respectively.

A diode-pumped acousto-optically (AO) Q-switched 1066 laser with a novel Nd:Gd0.69Y0.3NbO4 crystal under 879 nm pumping was demonstrated for the first time. In CW operation, the maximum output power of 7.5 W was obtained with a slope efficiency of 37.6%. The different modulation repetition rates from 5 kHz to 30 kHz in the pulsed Nd:GdYNbO4 laser were investigated. At an absorbed pump power of 7.44 W and a repetition rate of 10 kHz, the pulse width and peak power were 17.8 ns and 6.75 kW, respectively. We also got the highest repetition rate 61.214 kHz of this new mixed crystal.

In this paper, we present the acousto-optical (AO) Q-switched performance of a holmium (Ho):gadolinium tantalate (GdTaO4) (Ho:GTO) laser pumped by a thulium (Tm)-fiber laser emitting at 1.94 µm. In the efficient continuous wave (CW) regime, a maximum output power of 30.5 W at 2068.8 nm was achieved, corresponding to a slope efficiency of 74.9% with respect to the absorbed pump power. In the Q-switching regime, pulse energies of 2.4 mJ, 1.2 mJ, and 0.9 mJ were obtained with pulse repetition frequencies of 10 kHz, 20 kHz, and 30 kHz, respectively. The minimum pulse widths were 18 ns, 23 ns, and 26 ns, corresponding to peak powers of approximately 133.3 kW, 52.2 kW, and 34.6 kW, respectively.

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.

We demonstrate for the first time a Cr4+:YAG passively Q-switched 1066 nm pulse-burst laser under 879 nm direct pump with a novel Nd:Gd0.69Y0.3NbO4 crystal. The output laser characteristics with different pump repetition rates and different Cr4+:YAG initial transmission are studied. Without the Cr4+:YAG, we obtain a maximum output energy of 2.55 mJ at an absorbed pump energy of 5.79 mJ with the highest 48% slope efficiency. The pulse-burst laser contains a maximum of 7 pulses for a Cr4+:YAG initial transmission of 55% and a pump repetition rate of 1 kHz. The single-pulse energy and narrowest pulse width reach 160 μJ and 5.5 ns at 38.2 kHz, with a peak power of 32 kW.

A diode-pumped 1347 nm laser with a novel Nd:GdNbO4 crystal is demonstrated for the first time to our best knowledge. Laser performance around 1.3 μm under 879 nm laser diode pumping is investigated with different output mirrors, pump radii and repetition rates. A maximum average power of ∼ 373 mW at 1347 nm is achieved at 50 Hz, corresponding to an optical-to-optical efficiency of 5.5% and a slope efficiency of 6.8%.

In this work, LaNbO4 polycrystalline with monoclinic structure was prepared by traditional high-temperature solid-state reaction method. Its structure was determined by X-ray diffraction and its unit cell parameters were obtained with Rietveld refinement method. Its luminescence properties including excitation, emission spectrum as well luminescence lifetime were characterized in experiment. Besides, a systematic theoretical calculation based on the density function theory methods was performed on LaNbO4. The calculated band gap is in good agreement with that obtained in experiment. A comparison of the calculated and experimental refractive index and reflectivity between LaNbO4, YNbO4 and GdNbO4 was made. All the obtained results provide an essential understanding of LaNbO4.

Saturable absorber (SA) based on antimony telluride (Sb2Te3)-graphene oxide (GO) had been fabricated. We demonstrated a compact passively Q-switched Nd:GGG laser with the mixed Sb2Te3-GO SA. Stable Q-switching operation at a central wavelength of 1066 nm was performed. The shortest single pulse width of 237 ns with repetition rate of 72 kHz and the maximum output power for Q-switched operation of 408 mW was achieved under the pump power of 4.5 W, corresponding to the optical-to-optical conversion of 9.1%.

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.

In this work, GdNbO4 polycrystalline with monoclinic phase was prepared by traditional high-temperature solid-state reaction. Its structure was determined by X-ray diffraction and its unit cell parameters were obtained with Rietveld refinement method. Its luminescence properties (including absorbance, emission and luminescence lifetime) were investigated with experiment method and the CIE chromaticity coordinate was presented. Furthermore, a systematic theoretical calculation (including band gap, density of states and optical properties) based on the density function theory methods was performed on GdNbO4. Lastly, a comparison between experiment and calculated results was conducted. The calculated and experiment results obtained in this work can provide an essential understanding of GdNbO4 material.

1 at% Er 3+ doped Er: GdTaO 4 laser crystal with high optical quality was successfully grown by the Czochralski method. The structural parameters were obtained by the X-ray Rietveld refinement. A high crystalline quality of Er: GdTaO 4 was determined by the X-ray rocking curve. The transition intensity parameters of Er 3+ ions were fitted according to the absorption spectra along three principal polarization directions. The relatively larger emission cross section (1.022×10 −20 cm 2 ), long fluorescence lifetime ( 5.66 ms) and relatively weaker reabsorption phenomenon around 1.6 µm indicate that 1 at% Er: GdTaO 4 crystal can be used as a promising NIR laser material. Meanwhile, the stimulated emission cross-section spectra along three principal polarization directions were investigated for 4 I 13/2 → 4 I 15/2 transitions at 1.5–1.6 µm which indicates a great potential of Er: GdTaO 4 for multi-wavelength emission at 1.5–1.6 µm. In addition, the possibility of generating green and red lasers in Er: GdTaO 4 was also analyzed and evaluated.

A new mixed laser crystal Nd:Gd 0.69 Y 0.3 NbO 4 (Nd:GYNO) with high quality was grown successfully by Czochralski method. Its structure parameters are obtained by the X-ray Rietveld refinement method. The effective segregation coefficient of Nd 3+ ions is 0.61 in GYNO host. The maximum absorption cross section at 809 nm and peak emission cross section at 1065.6 nm of Nd:GYNO crystal are 11.6 × 10 −20 and 20.5 × 10 −20 cm 2 , respectively. The fluorescence lifetime of 4 F 3/2 manifold for Nd 3+ in Nd:GYNO crystal is fitted to be 156 μs. Diode-pumped continuous-wave laser operations at 1.06 μm with Nd:GYNO crystals cut perpendicular to crystallographic a , b , and c axes (denoted as a -, b - c -cut, respectively) were demonstrated. A maximum output power of 0.98 W was obtained with c -cut crystal, corresponding to an optical-to-optical conversion efficiency of 31.3% and a slope efficiency of 30.4%. All these results imply that the Nd:GYNO crystal has great potential application in low and even moderate lasers.

Nd:GdNbO4 crystal was grown successfully by the Czochralski (CZ) method. The continuous wave (CW) laser operation of Nd:GdNbO4 crystal at 1066 nm was reported for the first time. A maximum output power of 1.076 W with the incident power of 3.28 W was successfully obtained, corresponding to an optical-to-optical conversion efficiency of 32.8% and a slope efficiency of 35.3%. The absorption and fluorescence spectra of the crystal were measured at room temperature. By using the Judd-Ofelt approach, the intensity parameters were calculated to be 6.13 × 10−20, 1.56 × 10−20, and 2.81 × 10−20 cm2, respectively. The large absorption cross section (9.5 × 10−20 cm2) and broad absorption band (5 nm) at around 808 nm indicates that Nd:GdNbO4 crystal can be pumped efficiently by laser diodes (LD). The small emission cross section (9.3 × 10−20 cm2) and relatively long fluorescence lifetime (178 μs) of Nd3+ demonstrate good energy capacity of Nd:GdNbO4. All the results show that Nd:GdNbO4 crystal is a promising novel laser crystal suitable for LD pumping.

Based on Faraday effect we demonstrate a thulium fiber pumped continuous-wave single-longitudinal-mode laser with a new Ho:GdTaO

An erratum is presented to correct the wrong picture in our paper.

In this paper we report on the structure of Na 3 VO 2 B 6 O 11 (NVBO) single crystals which were investigated by XRD, polarized Raman spectra in the range from 10 to 1600 cm −1 and infrared spectrum (IR) in the range from 100 to 1600 cm −1 . Factor group analysis has been used to study the full vibrational representation of the crystal. More than 120 phonon modes have been obtained, which are related to B O and V O vibration in the trigonal planar BO 3 triangle groups and tetrahedral BO 4 /VO 4 groups. The high frequency bands located at 1300–1415 cm −1 are assigned to stretching modes of the trigonal planar BO 3 groups. Moreover, intense Raman modes located at 631 cm −1 is related to BO 3 bending vibration as well. The weak band at 1158 cm −1 (A 1 mode) and strong band at 431 cm −1 (A 1 mode) are attributed to asymmetric stretching and bending vibration mode of tetrahedral BO 4 groups respectively. The vibrational band at 765–738 cm −1 in the Raman spectra of NVBO crystal maybe related to the breathing vibration of the boroxol ring consisting of two BO 4 tetrahedra. In addition, we assigned the intense band 900 (A 1 mode) and 831 cm −1 (B 2 mode) are relative to the v 1 symmetric stretching vibration of VO 4 tetrahedra. And the middle intense band at 382 (A 1 mode) and 385 (A 2 mode) are due to O V O vibration in VO 4 tetrahedra.

In this work, harmonic mode locking in a laser diode pumped passively Q-switched mode-locked Nd:GdTaO4 1066 nm laser is presented by using Cr4+:YAG as saturable absorber. The average output power of the passively Q-switched mode-locked 1066 nm laser reaches 4.7 W with a repetition rate of 200.0 MHz and a pulse width of ~1.3 ns within a Q-switched envelope of 150.0 ns. By changing the Z-type cavity length, high-order harmonic mode locking operation of the passively Q-switched 1066 nm laser is conducted. The 3rd-order harmonically mode-locked 1066 nm laser yields a maximum average output power of 3.2 W and a pulse width of ~570 ps at 164.5 MHz repetition rate inside a Q-switched envelope of 419.7 ns long. The pulse repetition rate reaches 655.3 MHz in the 9th-order harmonically mode-locked 1066 nm laser.

This study investigated the laser performance of a Nd:GdYTaO4 crystal in continuous-wave and acousto-optically Q-switched operation. Laser performance comparison was conducted under 808 nm and 879 nm laser diode (LD) pumping. In continuous-wave operation, the maximum power at 1066 nm reached 4.4 W with an optical-to-optical efficiency of ~33.6% and the slope efficiency was ~35.9% under 808 nm laser diode pumping. In comparison, an output power of 7.7 W with an optical-to-optical efficiency of ~47.8% and a slope efficiency of ~48.3% were achieved in 879 nm LD pumped 1066 nm laser. Under 808 nm LD pumping, the Nd:GdYTaO4 crystal yielded an average output power of 1.1 W and a pulse width of 59.5 ns at the repetition rate of 30 kHz. By using direct pumping directly into the 4F3/2 emitting level, the average power was increased to 1.9 W and the pulse width was shortened to 33.0 ns at the repetition rate of 30 kHz.

This study investigated the laser performance of a Nd:GdTaO4 crystal for the 4F3/2→4I9/2 and 4F3/2→4I13/2 transitions at 928 nm and 1328 nm, respectively. A 5-mm-thick, 1.4 at.% Nd:GdTaO4 crystal was used in the experiments, under a pump at 879 nm, directly into the 4F3/2 emitting level. At a 10 Hz pump repetition rate, the maximum pulse energy at 928 nm reached 35.7 mJ, with an optical-to-optical efficiency of ~19.3%. When the pump repetition rate increased to 100 Hz, the laser pulse energy decreased to 13.5 mJ; the laser beam was characterised by M2 factors of Mx2 = 1.4 and My2 = 1.8 for the Ox and Oy axis, respectively. The Nd:GdTaO4 crystal yielded laser pulses at 1328 nm with a maximum energy of 9.7 mJ for operation at 10 Hz repetition rate; the overall optical-to-optical efficiency amounted to ~5.2%. Increasing the pump repetition rate to 100 Hz reduced the laser pulse energy to 5.8 mJ; the laser beam M2 factors were Mx2 = 1.2 and My2 = 1.4.

927.8nm laser operating on the 4F3/2 to 4I9/2 transition is investigated with a Nd:Gd0.3Ta0.69O4 crystal. The average power reaches 1.35 W under 879 nm pumping with beam quality factors of M x2 = 1.4 and My2=1.8.

In this paper, self-Q-switched (SQS) and passively Q-switched mode-locked (QML) dual-wavelength Nd:YSAG lasers are reported, that works at 1058.97 and 1061.49 nm, simultaneously. Till now, the performance on SQS, and passively QML operation by using black phosphorus (BP) in Nd:YSAG crystal lasers have not been reported as per the author’s knowledge. The Nd:YSAG laser SQS operation was realized by designing a simple plano-plano resonator cavity. The maximum output power of 0.471 W at absorbed pump power 2.64 W and the pulse duration was 885 ns. The Nd:YSAG laser QML operation was realized by designing a Z-type resonator cavity. The duration of mode-locked pulse inside the Q-switched envelop was estimated to be 235 ps with 96.5 MHz repetition rate at the absorbed pump power of 4.08 W in QML with black phosphorus saturable absorber (BP-SA).

Laser performances around 1.3 μm are investigated in 879 nm laser diode (LD) end pumped Nd

We demonstrated an 879-nm-diode-pumped Nd:Gd

A new promising 2.9 μm Tm,Ho:GdYTaO4 (Tm,Ho:GYTO) laser crystal was grown by the Czochralski method. The full width at half maximum (FWHM) of X-ray rocking curve on the (0 1 0) face is only 0.05°, which indicates that the crystal has high crystalline quality. The structure parameters of Tm,Ho:GYTO crystal were determined by Rietveld refinement method. Chemical etching is employed to investigate the defect structure of Tm,Ho:GYTO crystal with KOH etchant. The absorption, emission spectra, and level lifetimes were measured, and the corresponding absorption transitions were assigned. The absorption cross-section at 790 nm was calculated to be 2.04 × 10−20 cm2 and maximum emission-cross section at 2932 nm was 2.05 × 10−20 cm2. The level lifetimes of 5I6 and 5I7 are 131 μs and 4.09 ms, respectively. Compared with other hosts, such as Ho:YAG, the shorter lifetime of 5I7 and long lifetime of 5I6 in the Tm,Ho:GYTO crystal are easier to realize population inversion. The Tm–Ho energy transfer mechanism in GYTO is also demonstrated.

A new crystal of Yb-doped gadolinium niobate, 5 at.% Yb:GdNbO 4 , is grown by Czochralski method for the first time. The structure of Yb:GdNbO 4 is determined by Rietveld refinement to the X-ray powder diffraction data and it belongs to the monoclinic space group of I 2/a . With the center of 955 nm, the FWHM of absorption spectra is 57 nm and the absorption cross section is calculated to be 0.97 × 10 −20 cm 2 . Spectral parameters are calculated with absorption spectrum. In emission spectra, the strongest peak is at 1001 nm and the FWHM is 49 nm. In comparison with corresponding emission cross section of Yb:YSO and Yb:GSO, Yb:GdNbO 4 exhibits a relatively larger emission cross section. In addition, a maximal output power of 270 mW is obtained and the slope efficiency is 7.5%.

Recently, we proposed GdTaO4 as a promising high-density scintillator but the scintillation mechanism was still unknown. In this paper, we investigated the temperature-dependent luminescent properties of GdTaO4 crystal. The emission spectra are characterized by a broad band composed of two Gaussian components located at ~2.2 eV and ~2.7 eV of 8–300 K, which are both thermally quenched with the activation energy of 156 meV and 175 meV, respectively. These two bands are believed to be from different luminescent centers, judging from the excitation spectra, thermal activation energy and decay curves. Additionally, it was also found that the annealing atmosphere exerts little influence on the luminescence intensity. Based on the results, we tentatively assigned the high-energy band to self-trapped excitons (STE) localized in TaO 4 3 − groups and the low-energy band to relaxed excitons related to lattice imperfections.

A new laser medium Nd3+:GdTaO4 single crystal with high optical quality was grown successfully by the Czochralski method, and its high-efficiency laser operation at 1,066 nm was demonstrated for the first time. The absorption cross section of the crystal at 808 nm is 5.098 × 10−20 cm2, and the full width at half maximum of this absorption band is about 6 nm. Spectral properties are investigated by Judd–Ofelt theory. The stimulated emission cross section at 1,066 nm is 3.9 × 10−19 cm2, and the fluorescence lifetime of 4F3/2 level is 178.4 μs. A diode end-pumped Nd:GdTaO4 laser at 1,066 nm with the maximum output power of 2.5 W is achieved in the continuous-wave mode. The optical-to-optical conversion efficiency and slope efficiency are 34.6 and 36 %, respectively. In addition, the fluorescence branching ratio of 4F3/2 → 4I9/2 transition reaches 44.4 %, indicating that Nd:GdTaO4 may be an efficient laser medium at 920 nm. All the results demonstrate that Nd:GdTaO4 crystal is a good candidate for laser diode-pumped laser material.

Rare-earth tantalates, with high density and monoclinic structure, and niobates with monoclinic structure have been paid great attention as potential optical materials. In the last decade, we focused on the crystal growth technology of rare-earth tantalates and niobates and studied their luminescence and physical properties. A series of rare-earth tantalates and niobates crystals have been grown by the Czochralski method successfully. In this work, we summarize the research results on the crystal growth, scintillation, and laser properties of them, including the absorption and emission spectra, spectral parameters, energy levels structure, and so on. Most of the tantalates and niobates exhibit excellent luminescent properties, rich physical properties, and good chemical stability, indicating that they are potential outstanding scintillators and laser materials.

Based on Faraday effect we demonstrate a thulium fiber pumped continuous-wave single-longitudinal-mode laser with a new Ho:GdTaO4 crystal. By inserting a faraday rotator and a half-wave plate into the laser cavity, the single-longitudinal-mode output power of 392 mW at wavelength of 2068.33 nm was obtained in unidirectional Ho:GdTaO4 ring laser, corresponding to a slope efficiency of 60.2% respect to the absorbed pump power. Furthermore, utilizing the Ho:GdTaO4 power amplifier, the maximum single-longitudinal- mode output power of 1.02 W was achieved.

We report an 879 nm laser diode directly pumped passively Q-switched Nd:GdTaO4 laser at 1066 nm. The continuous-wave output power at 1066 nm reaches 5.6 W under an incident pump power of 12.8 W, corresponding to an optical-to-optical efficiency of 43.8% and a slope efficiency of 48.0%. By using Cr4+:YAG as the saturable absorber, passively Q-switched laser operation is conducted, yielding a highest pulse repetition frequency of 185 kHz and a maximum average power of 3.6 W. The shortest pulse width of 15.2 ns is achieved with a peak power of 2.34 kW at 33.7 kHz. The beam quality factors at the maximum average output power is measured to be Mx2 = 2.2, My2 = 1.5 by using knife-edge method. The thermal focal length and internal loss for Nd:GdTaO4 crystal is also investigated.

Large size high transparent TSAG and TSLAG single crystals of O 65 mm × 70 mm have been grown successfully by the Cz method. The refractive indices at 473, 532, 632.8 and 1064 nm are 1.9214 - 1.8817 for TSAG and 1.9242 - 1.8841 for TSLAG. Their Sellmeier equations are fitted. The average thermal expansion coefficients of TSAG and TSLAG at 300 – 373 K, 300 – 473 K, 300 – 573 K, 300 – 673 K, and 300 – 773 K are measured. The values of thermal expansion coefficients of TSAG and TLSAG crystals coincide within the measurement error (differ by 0.3–0.4%). The thermal diffusivity values of TSAG and TSLAG are 1.454 and 1.418 mm2 s−1 at 300 K, respectively. Calculated with the specific heat results, the values of thermal conductivity of TSAG and TSLAG are 4.45 and 4.20 W (m K)−1 at 300 K. Moreover, the Verdet constants of TSAG are 218, 152, and 65 rad/m/T at 532, 633, and 1064 nm, while those of TSLAG are 246, 146, and 56 rad/m/T, respectively. In further, the relationships between Verdet constant and wavelength of TSAG and TSLAG are obtained.

We demonstrate a continuous-wave 2.1-µm laser with a new Ho:GdTaO4 crystal pumped by a 1940.3-nm Tm fiber laser at room temperature. The maximum output power of 11.2 W at 2068.39 nm was achieved, corresponding to a slope efficiency of 72.9%. Moreover, the beam quality factor was measured to be about 1.4 at the maximum output level.

A promising 2.911 μm Yb,Ho:GdYTaO4 laser crystal was grown successfully by the Czochralski method for the first time. The crystal belongs to the monoclinic space group of I2/a (no. 15) and high crystalline quality is demonstrated by X-ray rocking curves. The effective segregation coefficient keff of Yb, Ho, and Y are 1.08, 0.96, and 0.9, respectively, all close to 1. Crystal density is measured to be 8.59 g cm−3 by the buoyancy method. Thermal property indicates that the Yb,Ho,Y:GdTaO4 crystal should be pumped along the c-axis in order to reduce the thermal lensing effect. Strong absorption in the range of 900–1000 nm and emission at 2911 nm are obtained in the as-grown crystal. In comparison with corresponding level lifetimes of Yb,Ho:YSGG, Tm,Ho:LuAG, Tm,Ho:YAG, and Ho:YAG, the Yb,Ho,Y:GdTaO4 crystal exhibits a relatively shorter lifetime of 7.298 ms for lower laser level 5I7 and longer lifetime of 419 μs for upper laser level 5I6, which are beneficial to realize population inversion and laser output.