Zhitai Jia

Femtosecond solid-state laser based on a few-layered black phosphorus saturable absorber.

In this Letter, a high-quality, few-layered black phosphorus (BP) saturable absorber (SA) was fabricated successfully, and a femtosecond solid-state laser modulated by BP-SA was experimentally demonstrated for the first time, to the best of our knowledge. Pulses as short as 272 fs were achieved with an average output power of 0.82 W, corresponding to the pulse energy of 6.48 nJ and peak power of 23.8 MW. So far, these represent the shortest pulse duration and highest output power ever obtained with a BP-based mode-locked solid-state laser. The results indicate the promising potential of few-layered BP-SA for applications in solid-state femtosecond mode-locked lasers.

Spectroscopy and Laser Properties of Yb-Doped Gd3AlxGa5-xO12 Crystal

We report the room-temperature spectroscopic properties and the continuous-wave and passive Q-switching laser operations of a new disorder crystal, Yb-doped Gd3AlxGa5-xO12 (Yb:GAGG). The peak absorption cross section is 0.56×10-20 cm2 at 942 nm, while the main emission band is centered at 1024 nm with a peak cross section of 1.05×10-20 cm2 and the full width at half maximum (FWHM) of 13.8 nm. The highest continuous-wave output power of 5.33 W is obtained with the optical–optical conversion efficiency of 41.6% and slope efficiency of 53.2%. In the passive Q-switching regime, with a V3+:YAG crystal as the saturable absorber, the highest output power, shortest pulse width, largest pulse energy and highest peak power achieved are 4.68 W, 24.7 ns, 93.8 µJ, and 3.8 kW, respectively. The results indicates that Yb:GAGG could be a potential laser crystal for high-power and ultrashort pulse generation.

Dual-Wavelength Passively Mode-Locked Nd:LGGG Laser With SESAM

A diode-end-pumped Nd:LGGG dual-wavelength synchronously mode-locked laser operation at 1.06 μm was demonstrated. The maximum average output power of 475 mW was obtained. The two wavelengths were simultaneous mode-locked at 1060.9 and 1062.7 nm with the pulse duration of 6.3 ps. A laser frequency beat was observed on top of the autocorrelation trace in the operation, corresponding to the 0.48 THz signal of stationary wave interference pattern.

High-efficiency femtosecond Yb:Gd 3 Al 0.5 Ga 4.5 O 12 mode-locked laser based on reduced graphene oxide

A diode-pumped Yb-doped Gd(3)Al(0.5)Ga(4.5)O(12) mode-locked bulk laser based on chemically reduced graphene oxide (RGO) has been demonstrated for the first time to our best knowledge. Pulses with duration of 643 fs were produced at the central wavelength of 1041.1 nm. A maximum average output power of 0.8 W was obtained from the RGO mode-locked laser, corresponding to a slope efficiency of 20.1% and a peak power of 27.6 kW. The results indicate that RGO is suitable for obtaining high-power and high-efficiency ultrafast lasers.

The origin of coloration of CaGdAlO4 crystals and its effect on their physical properties

CaGdAlO4 (CGA) single crystals have been grown in different oxygen concentration atmospheres by the Czochralski method. Crystals grown under an oxygen-containing atmosphere presented an inconsistent brown coloration. The origin of coloration was studied by density functional theory, and the simulated results show the oxygen defects and the absorption matched well with the experimental results. The brown coloration of CGA is due to the interstitial oxygen atoms. The fundamental properties of CGA crystals with different colors, including the crystal density, hardness, thermal and optical properties, were systematically investigated and compared when taking into account the effect of color center inside. The colorless CGA was grown under an inert gas atmosphere and exhibits a wide transparency range of 227–7140 nm. The maximum phonon energy was determined to be as low as 618 cm−1. The colorless CGA host crystal with a disordered structure, good thermal conductivity, low maximum phonon energy and wide transparency is promising for ultrafast ultraviolet and visible laser applications.

Efficient High-Peak-Power Wavelength-Switchable Femtosecond Yb:LGGG Laser

A systematic study of the spectral properties and ultrafast lasing characteristics of Yb:(LuxGd1-x)3Ga5O12(x = 0.062) (Yb:LGGG) disordered crystal was reported for the first time. The broad fluorescence spectral lines indicate a great potential of Yb:LGGG for tunable and ultrafast laser application. In the lasing experiment, a passively mode-locked Yb:LGGG laser was realized, which generated a maximum average power of 1.3 W with pulse duration of 324 fs at the central wavelength of 1029.6 nm, corresponding to a slope efficiency as high as 41.6%. The pulse energy and peak power were calculated to be 22.4 nJ and 69.2 kW. By optimizing the cavity design, the shortest pulse duration of 188 fs was achieved at the central wavelength of 1026.8 nm. In this case, the maximum average output power of 0.77 W was generated with a slope efficiency of 27.1%. The experimental results show the excellent potential of Yb:LGGG crystal for high-efficiency and high-peak-power femtosecond laser.

Linear and nonlinear optical properties of terbium calcium oxyborate single crystals

The linear and nonlinear optical properties of TbCa4O(BO3)3 (abbreviated as TbCOB) single crystals were investigated for the first time. The refractive indices of TbCOB at several wavelengths were measured by using the minimum deviation method and the parameters of Sellmeiers dispersion equation were determined from the experimental data. The complete set of six second-order nonlinear optical (NLO) coefficients of TbCOB single crystals were obtained using the Maker fringe (FM) technique, with the largest d32 being on the order of 1.65 pm/V. Moreover, the phase-matching (PM) configurations of second-order harmonic generation (SHG) in the principal planes were calculated, and the largest effective NLO coefficient is deff = 0.86 pm/V along (22.56°, 180°) PM direction. The SHG conversion efficiency from 1064 nm to 532 nm of 8 mm long crystal samples without AR coating along this direction was achieved 57.1% at 28.2 mW input power, and it has a small walk-off angle of 13.8 mrad. In addition, the comparison and discussion with GdCOB and YCOB were carried out.

Crystal growth and characterization of Nd 3+ :(La x Gd 1-x ) 3 Ga 5 O 12 laser crystal

A bulk mixed Nd3+:(LaxGd1-x)3Ga5O12 (Nd:LaGGG) laser crystal with dimensions of Ф 26 × 30 mm3 was successfully grown by the Czochralski (Cz) method. The structure and the effective segregation coefficients of Nd3+ and La3+ ions in the as-grown Nd:LaGGG crystal were measured. The thermal properties were also investigated as a function of temperature. In addition, the spectral properties were measured and the Judd-Ofelt (J-O) theory was applied to calculate the spectral parameters. In the 1062 nm CW laser operation, the maximum output power of 8.75 W was achieved. All the properties show that the Nd:LaGGG crystal is a promising laser materials.

High-power passively mode-locked laser at 1062.4 nm based on Nd:LaGGG disordered crystal

A diode-pumped passively continuous-wave mode-locked Nd:(La(x)Gd(1-x))3Ga5O12 (Nd:LaGGG) laser at 1062.4 nm with a semiconductor saturable absorber mirror was demonstrated for the first time, to the best of our knowledge. Pulses with duration of 12.78 ps were produced at a repetition rate of 59.8 MHz. A maximum average mode-locked output power of 3.18 W was obtained at the absorbed pumped power of 10.12 W, corresponding to a slope efficiency of 35.7% and a peak power of 4.2 kW. As far as we know, this is the highest power obtained in the passively mode-locking operation with Nd3+-doped disordered garnet crystals.

Crystal growth and optimization of Pr:CaGdAlO4 by the flux-Czochralski method

Pr:CaGdAlO4 (Pr:CGA) crystals have been grown and investigated for the first time. A Na+ flux was designed to improve the crystal quality in the Czochralski growth process. The effect of the addition of the Na+ flux on crystal quality has been investigated, and its beneficial impact on the crystallinity, optical homogeneity and thermal properties of the grown crystals has been demonstrated. The optical spectra of Pr:CGA have been measured in order to assess its potential for photonics applications. The intensities of the absorption transitions have been analyzed by means of the Judd–Ofelt approach and the intensity parameters, the branching ratios and the radiative lifetimes of the emitting states have been evaluated. These have been compared with the experimental values obtained from pulsed light measurements. All the properties indicate that the Pr:CGA crystal has great prospects in the applications of visible lasers.