Huaqiang Cai

Growth, thermal properties and laser operation of Nd:Ca3La2(BO3)(4): A new disordered laser crystal

A novel disordered laser crystal Nd:Ca(3)La(2)(BO(3))(4) is characterized including its crystal growth, structure, thermal properties, inhomogeneously broadened spectra, and laser performance, which result that this crystal should be a promising gain material for the high-power ultrashort pulsed neodymium laser. The complete set of anisotropic thermal properties were systematically studied for the first time. It has been found that thermal contraction happens in the c direction and all the thermal conductivities increase with temperature, indicating a glass-like behavior. Polarized absorption and fluorescence spectra of Nd:Ca(3)La(2)(BO(3))(4) crystal were measured at 298.15 K and 77.3 K, respectively. The results show that both the absorption and the emission spectra of Nd(3+) have been inhomogeneously broadened, and thus it is very promising to be used in laser systems to produce femtosecond pulses. CW laser operations at 1.06 μm along the three crystallographic directions has been demonstrated for the first time. A maximum power of 1.08 W with an optical conversion efficiency of 10.6% and slope efficiency of 12.4% was achieved in the a-cut sample.

Sub-80 femtosecond pulses generation from a diode-pumped mode-locked Nd:Ca 3 La 2 (BO 3 ) 4 disordered crystal laser

We experimentally demonstrated a diode-pumped sub-80 fs Nd:Ca3La2(BO3)4 disordered crystal laser. Pumping by an 808 nm fiber coupled laser diode, stable continuous-wave mode-locked pulses as short as 79 fs were achieved with a semiconductor saturable absorber mirror (SESAM). The ultrashort pulses had a repetition rate of ∼98.9  MHz at the central wavelength of about 1068 nm. To the best of our knowledge, this is the first demonstration of sub-100 fs pulses and the shortest mode-locked pulses generated from the Nd3+-doped crystal lasers.

251 fs pulse generation with a Nd3+-doped Ca3Gd2(BO3)4 disordered crystal

A diode-pumped passively mode-locked femtosecond Nd:Ca3Gd2(BO3)4 disordered crystal laser has been investigated for the first time, to our knowledge. The passive mode locking of the laser is initiated with a semiconductor saturable absorption mirror (SESAM). Stable mode-locked pulses with 251 fs pulse width, 87 MHz repetition rate, and 37 mW average output power have been demonstrated.

Low threshold photonic crystal lasing from a dye with high emission quantum yield and weak self-quenching

We demonstrate photonic crystal lasing with a low threshold power of ∼10 μJ per pulse from a dye with a high luminescence quantum yield and weak self-quenching effect. The effects of the stop bands of photonic crystals and concentration of doped dye on the threshold of lasing were systematically investigated.

Generation of sub-50fs soliton pulses from a mode-locked Yb,Na:CNGG disordered crystal laser

We experimentally demonstrated a diode-pumped sub-50 fs Yb,Na:CNGG disordered crystal laser. Pumped by a 980 nm distributed Bragg-reflector tapered diode laser and passively mode-locked with a semiconductor saturable absorber mirror (SESAM), soliton pulses as short as 62 fs and 45 fs were obtained without and with external compression, respectively. The ultrashort pulses had a repetition rate of ~104 MHz at the central wavelength of 1061 nm. To the best of our knowledge, this is the first demonstration of sub-50 fs pulses from the Yb3+-doped CNGG type disordered crystal lasers.

Evaluation of growth, thermal and spectroscopic properties of Yb 3+ -doped GSGG crystals for use in ultrashort pulsed and tunable lasers

A series of high quality Yb3+-doped gadolinium scandium gallium garnet (Yb:GSGG) single crystals with different Yb3+ ion concentration (7.5, 10, 15 and 30 at.%) has been grown by means of optical floating zone (OFZ). Crystal structure was analyzed with X-ray powder diffraction (XRPD), showing that the Yb:GSGG crystal possesses a cubic structure with space group Ia3d, and the lattice constants decrease linearly as the Yb3+ concentration increases. Effective elemental segregation coefficients and chemical composition were investigated by X-ray fluorescence (XRF), suggesting that some Yb3+ ions occupy the octahedral site when the Yb3+ ion concentration is higher than 10 at.%. The thermal properties of Yb:GSGG crystals were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficients. Thermal conductivity was then calculated, and it exhibits a tendency to decrease with increasing Yb3+ ion concentration. Spectroscopic characterization of Yb:GSGG crystals was performed at room temperature (RT), and the stimulated emission cross section was calculated using the reciprocity method (RM) and the Fuchtbauer−Ladenburg (F−L) formula, respectively. In comparison with the radiative lifetime of the 2F5/2→2F7/2 transition, the effect of radiation trapping on the fluorescence lifetime is discussed. These research results indicate that Yb:GSGG can be regarded as a promising candidate for use in an ultrashort pulsed and tunable laser.

Comparative study of the spectroscopic and laser properties of Tm 3+ , Na + (Li + )-codoped Ca 3 Nb 1.5 Ga 3.5 O 12 -type disordered garnet crystals for mode-locked lasers

Tm3+,X+-codoped disordered calcium niobium garnet crystals, Ca3Nb2-xGa3+xO12 (CNGG), where X+ is an alkali cation, Na+ or Li+ (shortly Tm:CNNGG and Tm:CLNGG, respectively), are grown by the Czochralski method. A comparative study of their spectroscopic and laser properties is performed. Raman spectra are also studied. For Tm:CNNGG, the Judd-Ofelt parameters for the Tm3+ dopant ion are Ω2 = 1.847, Ω4 = 1.558 and Ω6 = 0.862 [10−20 cm2] and the radiative lifetime of the 3F4 state is 4.11 ms. The absorption, stimulated-emission (σSE) and gain cross-sections are determined for the 3H6 ↔ 3F4 Tm3+-ion transition. For Tm:CNNGG, the maximum σSE is 0.49 × 10−20 cm2 at 1867 nm. Both crystals exhibit flat and broad gain spectra extending beyond 2 µm. A compact diode-pumped Tm:CNNGG laser has generated 1.05 W at 2007.7 nm with a slope efficiency of 35%. Broadband tuning of Tm:CNNGG and Tm:CLNGG lasers (tuning ranges of 168 nm and 224 nm, respectively), was demonstrated. The Tm3+,X+-codoped CNGG crystals are the promising for sub-100 fs pulse generation at ~2 μm.

Crystal growth and properties of the disordered crystal Yb:SrLaAlO4: a promising candidate for high-power ultrashort pulse lasers

A high quality Yb3+-doped strontium lanthanum aluminate crystal, Yb:SrLaAlO4 (Yb:SLA) is grown by the Czochralski method. It is tetragonal (sp. gr. I4/mmm, a = b = 3.7536 A, c = 12.6253 A). Room- and low-temperature spectroscopy of Yb3+ ions in this crystal are studied. The Stark splitting is resolved. Absorption, stimulated-emission (SE) and gain cross-sections are determined with polarized light. In the spectral range of laser emission, the maximum σSE is 0.57 × 10−20 cm2 at 1047 nm for σ polarization. The polarized Raman spectra of Yb:SLA are presented. Thermal properties of Yb:SLA are characterized in terms of the linear thermal expansion, specific heat and thermal conductivity. The latter is as high as 6.06 and 4.30 W m−1 K−1 along the a- and c-axes, respectively (at room temperature). Broadband tuning of a continuous-wave (CW) Yb:SLA laser, from 1011 to 1082 nm has been achieved. Due to its good thermal properties, broad and smooth gain spectra, Yb:LSA is a promising material for power-scalable, broadly tunable CW and sub-100 fs mode-locked lasers at ∼1 μm.