Degao Zhong

Spectroscopic properties and continuous-wave laser operation of Yb:LuPO 4 crystal

For the first time, and to the best of our knowledge, we report a continuous-wave (cw) laser operation of Yb:LuPO₄ crystal, demonstrated at room temperature in a compact plano-concave resonator end pumped by a diode laser. 1.61 W of cw output power around 1039 nm were generated with 2.40 W of pump power at 976 nm absorbed in a 0.3 mm thick crystal, leading to an optical-to-optical efficiency of 67%, whereas the slope efficiency was 75%. Polarized absorption and emission cross-section spectra are also presented and discussed in detail.

Columnar crystal of Yb:LuPO 4 for high-power miniature rod lasers

We report, for the first time to our knowledge, on the laser performance of a sort of miniature columnar Yb:LuPO4 crystal grown from spontaneous nucleation in high-temperature solution. With a very compact resonator longitudinally pumped by a 976-nm diode laser, continuous-wave laser operation is demonstrated with a 2-mm long tiny crystal rod, with output coupling changed over a wide range from 0.5% to 62%, generating a maximum output power of 5.3 W with an optical-to-optical efficiency of 40%, while the slope efficiency being 50%.

Repetitively Q-switched laser operation of a miniature Yb:LuPO 4 crystal rod

We report on efficient repetitively Q-switched laser operation of a miniature Yb:LuPO4 crystal rod with emission wavelengths ranging from 1000 to 1010 nm, at different repetition rates over a range of 1−50 kHz. An average output power of 6.55 W was produced at 50 kHz of repetition rate, with a slope efficiency of 40%; in a low-repetition-rate operation at 2 kHz, the maximum pulsed output power generated was 1.43 W, with pulse energy, duration, and peak power being, respectively, 0.715 mJ, 12.5 ns, and 57.2 kW.

Synthesis, growth, defects and laser action of Yb:Y0.71Lu0.29VO4 crystals

Polycrystalline materials of REVO4 (RE = Y, Lu, Yb) were synthesized by liquid-phase reaction. An Yb-doped Yb:Y0.71Lu0.29VO4 crystal was grown by the Czochralski method. Dislocations and low-angle boundaries were revealed by chemical etching and transmission electron microscopy (TEM). Continuous-wave (cw) laser action was achieved in the range of 1020.7–1029.0 nm by using a high-power diode laser as the pump source. A cw laser output power of 1.09 W with a slope efficiency of 21.6% was demonstrated for this 0.5 at.% Yb-doped Yb:Y0.79Lu0.21VO4 mixed crystal.

Room temperature noncritical phase matching fourth harmonic generation properties of ADP, DADP, and DKDP crystals

Noncritical phase-matching (NCPM) fourth harmonic generation (FHG) of a 1053 nm laser was realized at room temperature on an ammonium dihydrogen phosphate (ADP), 35% deuterated DADP and 62% deuterated potassium dihydrogen phosphate (DKDP) crystals grown by point-seed rapid growth method. The NCPM temperature is 33.7°C for ADP, 32.1°C for DADP, and 31°C for DKDP crystal. The temperature, angle tuning properties, and performance in NCPM FHG of ADP DADP and DKDP crystals are calculated and compared in detail. The 2ω-to-4ω conversion efficiency has been demonstrated up to 67% with ADP crystal, 63.45% with DADP crystal, and 63.78% with DKDP crystal. Large-aperture high-efficiency fourth harmonic generation would be realized by improving the temperature control and crystal quality with all these crystals and all these results could be a good reference in crystal chosen of NCPM FHG.

Growth, spectroscopic properties, and laser action of Yb:YPO 4 crystal

Good-quality single crystals of Yb:YPO4 were grown in a high-temperature solution. Polarized absorption and emission cross-section spectra were determined by use of a plate-shaped crystal of 1.8 mm in thickness. Efficient continuous-wave laser action was achieved under diode end-pumping conditions, with output coupling changed in a wide range of 0.5%−40%. A maximum output power of 3.62 W was produced with a 1.0 mm thick crystal, with an optical-to-optical efficiency of 36%.

Growth, structural, thermal, dielectric and optical studies on HBST crystal: A potential THz emitter

The efficient organic nonlinear optical material 4-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (HBST) was grown from methanol by slope nucleation method combined with slow cooling (SNM-SC) for the first time. The optimum growth conditions based on the cooling rate was further investigated. The single crystal X-ray diffraction (XRD) revealed that the chromophores of HBST crystal make an angle of about 33° with respect to the a-axis, which is close to the optimum of Terahertz (THz)-wave generation and electro-optics applications. NMR and FT-IR spectral studies have been performed to ascertain various functional groups present in the sample. Futhermore, the thermal stability and decomposition stages were analyzed through TG-DTA and DSC techniques. The dielectric constant and dielectric loss of HBST crystal have been studied. Critical optical properties like the absorption coefficient, refractive index, cut-off wavelength and band gap energy were calculated. Photoluminescence (PL) exication studies indicated green emission occured at 507nm. All the results of HBST crystal make it a promising candidate in the fields of optoelectronic and the generation of THz.

Li2Gd4(MoO4)7 crystal preparation and spectral properties applied to 2.0 μm lasers

A Tm3+/Ho3+ co-doped Li2Gd4(MoO4)7 (Tm/Ho:LGMO) crystal was grown using the Czochralski method. A systematic investigation of the structure characteristics, polarized absorption spectra, fluorescence spectra and lifetimes, and emission and gain cross-sections of this crystal was reported for the first time. The main spectroscopic parameters of Ho3+ ions in the grown crystal, such as J–O intensity parameters, line and oscillator strengths, spontaneous transition rates, fluorescence branching ratios and radiative lifetimes, were calculated using the Judd–Ofelt theory. Due to the statistical distributions of Li+, Gd3+ and vacancies, the absorption and emission spectra are strongly inhomogeneously broadened. The wide absorption bands at around 795 nm are quite desirable for the efficient pumping of AlGaAs laser diodes whose emission wavelengths usually change with the operating temperature. The broad emission bands from 1600 to 2200 nm allow wide tunability of laser oscillation. All the results reveal that the Tm/Ho:LGMO crystal is a promising gain medium for tunable and ultrafast pulse lasers at 2.0 μm.

Growth, structural, spectral and high-power continuous-wave laser operation of Yb 0.11 Gd 0.89 COB crystal

Abstract A Yb 0.11 Gd 0.89 Ca 4 O(BO 3 ) 3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb 0.11 Gd 0.89 COB were calculated to be a =0.8089(7) nm, b =1.5987(6) nm, c =0.3545(8) nm, β =101.22°. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb 0.11 Gd 0.89 COB crystal was 0.79×10 −20 cm 2 , which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10 −20 cm 2 . The radiative lifetime τ rad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb 3+ in the Yb 0.11 Gd 0.89 COB crystal field at room temperature was determined. The ground-state energy level 2 F 7/2 splitting was calculated to be as large as 1004 cm −1 and the zero-line energy was 10246 cm −1 . A maximum output power of 9.35 W was achieved in continuous-wave (CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb 0.11 Gd 0.89 COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.

SEM, Chemical Etching and THz Wave Generation of 4-Dimethylamino-N-methyl-4-stilbazolium Tosylate (DAST) Single Crystals

The 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal which was candidate for generating and detecting terahertz (THz) wave was grown by slope nucleation method (SNM). The functional groups of DAST were identified by Fourier Transform Infrared (FTIR) studies. Macroscopic steps and streaks on the (001) face were found by scanning electron microscope (SEM). Different patterns of etch pits under different chemical etchants were studied by optical microscope. Widely tunable THz waves ranging from 0.38 to 18.10 THz were generated from 0.5 mm-thick DAST crystal. The maximum output energy was 345.4 nJ/pulse at 3.39 THz and the conversion efficiency was 8.44 × 10–5.