Zhongben Pan

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.

Passively Q-switched ytterbium-doped ScBO3 laser with black phosphorus saturable absorber

Abstract. We demonstrate a passively Q-switched Yb3+-doped ScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4  μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics.

Thermo-optic dispersion formulas for YCOB and GdCOB laser host crystals

We report on a comparative study of anisotropy and dispersion of thermo-optic coefficients, dn/dT, and thermal coefficients of the optical path for monoclinic oxoborate YCOB and GdCOB laser host crystals. Near 1 μm, all dn/dT coefficients are found to be negative: dnX/dT = –1.2, dnY/dT = –3.7 and dnZ/dT = –2.5 × 10−6 K−1 for YCOB, dnX/dT = –3.8, dnY/dT = –4.8 and dnZ/dT = –3.7 × 10−6 K−1 for GdCOB. Thermo-optic dispersion formulas are derived for these crystals in the spectral range of 0.4–2 μm. The existence of athermal directions is predicted for both YCOB and GdCOB.

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.

Exploration of Yb 3+ :ScBO 3 - a novel laser crystal in the rare-earth ion doped orthoborate system

Growth of optical-quality crystals with a borate anionic group and small-diameter cations is challenging. By compensating for the volatilization of boracic acid, an optical-quality Yb3+:ScBO3 laser crystal suitable for laser applications has been grown by the Czochralski method. The thermal and spectral properties of Yb3+:ScBO3 were experimentally and theoretically studied, including the thermal expansion, thermal diffusivity, specific heat, thermal conductivity, and the absorption and low-temperature emission spectra. The results indicate that this crystal exhibits a thermal conductivity that increases with temperature, and large energy storage properties that indicate promise for utilization in moderate power lasers. A continuous-wave Yb3+:ScBO3 crystal laser has, to the best of our knowledge, been demonstrated for the first time, with a maximum output power of 106 mW. All the results are indicative of a novel promising laser medium for applications in low and even moderate power lasers.

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.

High-energy passively Q-switched laser operation of Yb:Ca 3 La 2 (BO 3 ) 4 disordered crystal

Efficient high-energy passively Q-switched laser operation was demonstrated with Yb:Ca₃La₂(BO₃)₄ disordered crystal, producing an average output power of 3.0 W at 1018.7 nm, at a pulse repetition frequency of 5.0 kHz; the resulting pulse energy, duration, and peak power were 600 μJ, 5.3 ns, and 113.2 kW, respectively.

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.