Xiaobo Qian

Spectroscopic properties and CW laser operation of Nd, Y-codoped CaF2 single crystals

Spectroscopic properties of Nd:CaF2 crystals with different doping concentrations of Nd3+ and codoping concentrations of Y3+ were investigated. The effect of codoping with Y3+ ions on the absorption and emission spectra, emission lifetimes, quantum efficiency, and emission cross sections of Nd3+ were studied. In particular, codoping with Y3+ ions increases the width of the emission lines over that found with Nd-doped glasses, and allows true CW laser operation around 1.06 μm.

Nd,Y:CaF2 laser crystals: novel spectral properties and laser performance from a controlled local structure

A series of Nd,Y:CaF2 single crystals grown using the TGT method were studied systematically by absorption, excitation and luminescence spectroscopy, and the extended X-ray absorption fine structure (EXAFS) technique. The incorporation of Y3+ substantially manipulated the local structure of Nd ions in the CaF2 crystal lattice. Subsequently, the changes in the local structure of the Nd3+ ions induced substantial variations of the photoluminescence parameters, including FWHM, cross sections, lifetimes and quantum efficiency. Preliminary laser experiments were carried out with 0.5% Nd,10% Y:CaF2, 0.8% Nd,5% Y:CaF2 and 0.8% Nd,10% Y:CaF2 crystals under LD pumping; true CW laser operation was achieved with slope efficiencies of 30.1%, 19.3% and 24.9%, respectively.

Characteristics of a diode-pumped Yb:CaF2-SrF2 mode-locked laser using a carbon nanotube absorber

Yb:CaF2–SrF2 disordered crystals are successfully grown by the TGT method. By using a double-walled carbon nanotube saturable absorber (DWCNT-SA), the continuous-wave mode-locked (CWML) laser properties of Yb:CaF2–SrF2 crystals are demonstrated under diode pumping for the first time. The mode-locked laser delivers pulses as short as 5 ps at a center wavelength of 1045.5 nm without any dispersion compensation. The oscillator operating at a repetition rate of ~87 MHz delivers 292 mW average output power.

Spectroscopic properties of Yb-doped CaF2–YF3 solid-solution laser crystal

The spectroscopic properties of Yb:CaF2–YF3 disordered crystals obtained by the vertical Bridgman method were studied. The 3 at.% Yb, 3 at.% Y:CaF2 crystal absorption cross section σabs centered at 974 nm reached 7.2 × 10−21 cm2 and the fluorescence lifetime was 3.54 ms at room temperature. Experimental results show that co-doping Y3+ ions at different Y:Yb ratios can modulate the spectroscopy and lengthen the luminescence lifetime of Yb3+ ions in the CaF2 lattice. There are three main kinds of lattice in the 3 at.% Yb, 3 at.% Y:CaF2 crystal, as concluded from the low-temperature spectra.

Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF2 single crystals.

The spectral properties and laser performance of Er:SrF2 single crystals were investigated and compared with Er:CaF2. Er:SrF2 crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er3+:4I11/2 level) than those of Er:CaF2 crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF2 single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF2 with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.

Influence of thermal treatment on the near-infrared broadband luminescence of Bi:CsI crystals

Near-infrared (NIR) emitting active centers can exist abundant in Bi:CsI crystal. In addition, Bi:CsI have the simplest crystal structure, body-centered cubic (BCC). In this paper, annealing and quenching treatments were carried out in detail to identify the nature of NIR emitting active centers in Bi:CsI crystals. The changes of absorption and emission spectra with increasing the thermal treatment temperature indicated that the two NIR emission bands at 1210 nm and 1580 nm were related to Bi+ and Bi2+, respectively. Besides, the assignments of absorption bands and the thermal behaviors of Bi3+, Bi2+, Bi+ and Bi2+ were discussed as well.

Dual-wavelength continuous-wave and passively Q-switched Nd,Y:SrF2 ceramic laser

Abstract. A polycrystalline ceramic based on an Nd,Y:SrF2 single crystal was successfully fabricated and its laser performance was experimentally investigated. We obtained dual-wavelength continuous-wave operation at the wavelengths of 1050.5 and 1058.0 nm. The maximum output power and slope efficiency were 750 mW and 31.5%, respectively. In the passively Q-switched operation, the shortest pulse with a 169-ns duration was also obtained, and the corresponding maximum repetition rate and single pulse energy were 7.3 kHz and 19.2  μJ, respectively.

Picosecond pulse generation from a Yb:CaF2–YF3 mode-locked laser

We experimentally investigated a picosecond (ps) diode-pumped passively mode-locked (ML) laser operation of a 5 at.% Yb, 5 at.% Y:CaF2 crystal obtained by the vertical Bridgman method. Without extra negative dispersion elements, the ML laser emitted stable 1.3 ps pulses at a repetition rate of 60 MHz with 514 mW average output power under the absorbed pump power of 6.43 W. The continuous wave (CW) operation was also reported with the average output power of 1.48 W, corresponding to the optical slope efficiency of 31.3%.

Diode-pumped tri-wavelength synchronously mode-locked Yb,Y:CaF_2 laser

A tri-wavelength synchronous mode-locking operation of a diode-pumped Yb,Y:CaF2 laser has been investigated by using a semiconductor saturable absorber mirror at 1 μm. The tri-wavelength synchronous mode-locking pulses were centered at 1045.7, 1047.6, and 1049.5 nm. An interference pattern was obtained in the autocorrelation trace, where the beat pulse width was 3.2 ps and the repetition rate was 0.52 THz. The maximum average output power was 196 mW with pulse width 120 ps and repetition rate of 89 MHz.

Femtosecond diode-pumped mode-locked neodymium lasers

Fluoride-type crystals (CaF2, SrF2) doped with neodymium Nd3+ and codoped with buffer ions for breaking clusters of active ions and increasing fluorescence efficiency, present interesting alternative as laser active media for the diode-pumped mode-locked lasers. In comparison with widely used materials as Nd:YAG or Nd:YVO4, they have broad emission spectra as well as longer fluorescence lifetime, in comparison with Nd:glass, SrF2 and CaF2 have better thermal conductivity. In spite of the fact, that this thermal conductivity decreases with Nd3+ doping concentration, these crystals are alternative for the Nd:glass in subpicosecond mode-locked laser systems. In this paper we review the basic results reported recently on these active materials and in the second part we present our results achieved in low power diode pumped passively mode locked lasers with Nd,La:CaF2 and Nd,Y:SrF2 crystals. The pulses as short as 258 fs at wavelength of 1057 nm were obtained in the first case, while 5 ps long pulses at 1065 nm were generated from the second laser system.