Zhenyu You

Spectroscopic investigations of highly doped Er3+ : GGG and Er3+/Pr3+ : GGG crystals

Heavily Er3+-doped and Er3+/Pr3+ co-doped Gd3Ga5O12 (abbreviated as Er : GGG and Er,Pr : GGG, respectively) laser crystals were synthesized by the Czochralski method. The synthesized laser crystals were characterized by absorption, up-conversion fluorescence, near-infrared (NIR) and mid-infrared (Mid-IR) fluorescence, and luminescence decay measurements. The optical parameters related to absorption and emission cross-sections and fluorescence lifetimes were evaluated and compared. It was found that the up-conversion and NIR fluorescence weaken, at the same time Mid-IR fluorescence intensity strengthens with the increment of Er dopant concentration or co-doping with Pr3+ in Er : GGG crystals. Furthermore, the self-termination bottleneck was broken successfully in the Er,Pr : GGG crystal, and the energy transfer efficiencies of Er3+ : 4I11/2 → Pr3+ : 1G4 and Er3+ : 4I13/2 → Pr3+ : 3F4 were determined.

Self-frequency tripling from two cascaded second-order nonlinearities in GdAl3(BO3)4:Nd3+

We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the 4F3/2→4I11/2 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm.

Spectroscopic properties of Er3+ transitions in SrWO4 crystal

Er3+:SrWO4 crystal of good optical quality was grown by Czochralski technique method. Polarized absorption and emission spectra of Er3+ ions in SrWO4 crystal have been investigated. The Judd-Ofelt (JO) theory was applied to the polarized absorption spectra of Er3+:SrWO4 to obtain the three JO parameters: Ω2=7.41×10−20cm2, Ω4=0.25×10−20cm2, and Ω6=1.71×10−20cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Er3+:SrWO4 were calculated. The stimulated emission cross sections of the potential laser transitions at 1535nm were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula, and the potential laser gain versus wavelength for the I13∕24→I15∕24 transition has been estimated and discussed.

Optical properties of Dy3+ ion in GGG laser crystal

High optical quality Dy3+-doped Gd3Ga5O12 (abbreviated as Dy : GGG below) crystal was grown by the Czochralski technique along the (1 1 1) orientation. The absorption spectrum, fluorescence spectrum and fluorescence decay curve of Dy : GGG have been recorded at room temperature. Based on the Judd–Ofelt (J–O) theory, the intensity parameters from the measured line strengths were determined. The J–O parameters were used to predict radiative transition probabilities, radiative lifetime and branching ratios for various excited levels of the Dy : GGG crystal. In the visible region, one intense fluorescence band was observed at 581 nm, corresponding to the 4F9/2 → 6H13/2 transition. The room-temperature fluorescence lifetime of this transition of Dy3+ ion in the GGG crystal was measured to be 0.79 ms, and the luminescent quantum efficiency of the 4F9/2 level was evaluated to be 71.4 %. The emission cross-sections of the 4F9/2 → 6H13/2 transition were estimated by the use of the Fuchtbauer–Ladengurg method. The research on the emission at 581 nm indicates the possibility of using a commercially available laser diode of 353 nm as a pumping source for a solid-state yellow laser.

Benefit of Pr 3+ ions to the spectral properties of Pr 3+ /Er 3+ :CaGdAlO 4 crystal for a 2.7 μm laser

The spectra of Er3+:CaGdAlO4 and Pr3+/Er3+:CaGdAlO4 crystals were measured under the same conditions. With the presence of Pr3+ ions, the intensities of the green, red upconversion and near-infrared emissions are dramatically reduced to 1/20, 1/150, and 1/8.5 of those for Er3+:CaGdAlO4. Furthermore, the lifetimes of 4I11/2 upper and 4I13/2 lower laser levels fall from 450 and 982 μs to 84.8 and 74.3 μs. It is obvious that the self-saturation for Er3+ 2.7 μm laser is effectively suppressed. The energy transfer efficiencies and coefficients of Er3+→Pr3+ are also calculated. These results indicate that Pr3+ codoping is beneficial in achieving 2.7 μm laser in Pr3+/Er3+:CaGdAlO4 crystal.

Diode-pumped laser operation of Yb3+-doped Y2Ca3B4O12 crystal

We report in the present paper the Yb3+-doped Y2Ca3B4O12 diode-pumped laser operation in both continuous-wave (cw) and passively Q-switched modes. The differential slopes of the cw output power are in the 22%–40% range under different experimental conditions. Continuous tuning of the laser wavelength is obtained in the 1020–1057 nm range, in agreement with the broad emission spectra. In pulsed regime the repetition rate occurs up to 1.6 kHz and pulse energies of 30–75 μJ with about 40 ns duration are obtained.

Activation effect of Ho 3+ at 2.84 μm MIR luminescence by Yb 3+ ions in GGG crystal

The use of Yb(3+) co-doping for the enhancement of Ho(3+):(5)I(6)→(5)I(7) mid-IR (MIR) emissions was investigated in GGG crystal for the first time. It is established that Yb(3+) highly increases Ho(3+) 2.84 μm emissions by transforming pump energy from the Yb(3+):(2)F(5/2) level to the laser upper level (5)I(6) of Ho(3+). The energy-transfer efficiency from Yb(3+):(2)F(5/2) to Ho(3+):(5)I(6) is calculated to be 96.2%. The absorption cross section, emission cross section, and fluorescence quantum efficiency are estimated and discussed. It is concluded that the Yb, Ho:GGG crystal is promising material for an LD-pumped 2.84 μm laser application.

Dual function of Nd 3+ in Nd,Er:LuYSGG crystal for LD pumped ~3.0 μm mid-infrared laser

Enhanced ~3.0 μm emission corresponding to Er3+:4I11/2→4I13/2 was achieved in Nd3+/Er3+ co-doped Lu0.15Y2.85Sc2Ga3O12 (abbr. as Nd,Er:LuYSGG) crystal under 808 nm pumping. As compared with Er:YSGG crystal, the absorption pump efficiency of Nd,Er:LuYSGG crystal is greatly improved and thus ~3.0 μm emission is enhanced by 2.2 times owing to the sensitization of Nd3+, at the same time, Nd3+ as deactivator quenches ~1.5 μm emission from Er3+:4I13/2 level and thus inhibit the self-termination effect successfully. The energy transfer efficiencies of Nd: 4F3/2→Er: 4I11/2 and Er: 4I13/2→Nd:4I15/2 are estimated to be 91.6% and nearly 100%, respectively. These results indicate that the introduction of Nd3+ is very helpful for achieving ~3.0 μm laser in Nd,Er:LuYSGG crystal.

Ultrasensitive nonlinear absorption response of large-size topological insulator and application in low-threshold bulk pulsed lasers

Dirac-like topological insulators have attracted strong interest in optoelectronic application because of their unusual and startling properties. Here we report for the first time that the pure topological insulator Bi2Te3 exhibited a naturally ultrasensitive nonlinear absorption response to photoexcitation. The Bi2Te3 sheets with lateral size up to a few micrometers showed extremely low saturation absorption intensities of only 1.1 W/cm2 at 1.0 and 1.3 μm, respectively. Benefiting from this sensitive response, a Q-switching pulsed laser was achieved in a 1.0 μm Nd:YVO4 laser where the threshold absorbed pump power was only 31 mW. This is the lowest threshold in Q-switched solid-state bulk lasers to the best of our knowledge. A pulse duration of 97 ns was observed with an average power of 26.1 mW. A Q-switched laser at 1.3 μm was also realized with a pulse duration as short as 93 ns. Moreover, the mode locking operation was demonstrated. These results strongly exhibit that Bi2Te3 is a promising optical device for constructing broadband, miniature and integrated high-energy pulsed laser systems with low power consumption. Our work clearly points out a significantly potential avenue for the development of two-dimensional-material-based broadband ultrasensitive photodetector and other optoelectronic devices.

Mid-infrared emission in Dy:YAlO 3 crystal

In this work, we report on the spectroscopic properties of Dy3+ doped YAlO3 crystal grown by Czochralski technique. The Judd-Ofelt theory was performed based on the measured polarized absorption spectra. Under optical pumping at 1300 nm, Dy:YAP crystal exhibited a broad MIR emission centered at 3020 nm, with a bandwidth of 520 nm at full width half maximum. The decay lifetime of the 6H13/2 level was measured to be 8.88 ms, and the corresponding quantum efficiency evaluated was 57.9%. The studied optical gain properties indicate that Dy:YAlO3 crystal could be a potential candidate for solid-state mid-infrared laser applications.