Degang Xu

104 W high stability green laser generation by using diode laser pumped intracavity frequency-doubling Q-switched composite ceramic Nd:YAG laser

By use of CW diode laser stacked arrays, side-pumping Q-switched composite ceramic Nd:YAG rod laser based on a type II KTP crystal intracavity frequency-doubled, a high power high stability green laser has been demonstrated. Average output power of 104 W is obtained at a repetition rate of 10.6 kHz with a diode-to-green optical conversion efficiency of 10.9%. For the average output power of about 100 W, the measured pulse width is 132 ns with power fluctuation of less than 0.2%. The experimental results show that the green laser system using this novel ceramic Nd:YAG offers better laser performance and output stability than the traditional single Nd:YAG crystal green laser system with the same operating conditions and experimental configuration.

Efficient diode-end-pumped dual-wavelength Nd, Gd:YSGG laser

We demonstrate a dual-wavelength laser based on a new laser material-Nd, Gd:YSGG, or Nd:GYSGG for short-for the first time to our knowledge. Besides its attractive properties such as antiradiation, high segregation coefficient, etc., this kind of laser crystal also shows excellent laser performance. For continuous-wave operation, the maximum output power is 10.1 W with the absorbed power of 18.45 W at 808 nm, corresponding to the slope efficiency of nearly 60%. The maximum single pulse energy and peak power reach 277 μJ and 4.6 kW (60 ns) when the absorbed pump power is 11.4 W for acousto-optic Q-switched operation.

Experimental study on a high conversion efficiency, low threshold, high-repetition-rate periodically poled lithium niobate optical parametric generator

A high-conversion-efficiency, low-threshold, quasi-continuous-wave optical parametric generator (OPG) based on a periodically poled lithium niobate (PPLN) crystal is presented. Pumped by an acousto-optically Q-switched 1064 nm Nd:YAG laser with a power output of 848 mW, the OPG generated an output power of 452 mW for the signal and the idle waves, achieving an internal conversion efficiency of 62.7% and a slope efficiency of 75.6%. To the best of our knowledge, this is the highest efficiency ever reported for single-pass, quasi-continuous-wave OPGs by using periodically poled crystals.

A Reflective Photonic Crystal Fiber Temperature Sensor Probe Based on Infiltration with Liquid Mixtures

In this paper, a reflective photonic crystal fiber (PCF) sensor probe for temperature measurement has been demonstrated both theoretically and experimentally. The performance of the device depends on the intensity modulation of the optical signal by liquid mixtures infiltrated into the air holes of commercial LMA-8 PCFs. The effective mode field area and the confinement loss of the probe are both proved highly temperature-dependent based on the finite element method (FEM). The experimental results show that the reflected power exhibits a linear response with a temperature sensitivity of about 1 dB/°C. The sensor probe presents a tunable temperature sensitive range due to the concentration of the mixture components. Further research illustrates that with appropriate mixtures of liquids, the probe could be developed as a cryogenic temperature sensor. The temperature sensitivity is about 0.75 dB/°C. Such a configuration is promising for a portable, low-power and all-in-fiber device for temperature or refractive index monitoring in chemical or biosensing applications.

Widely tunable and monochromatic terahertz difference frequency generation with organic crystal DSTMS

Widely tunable and monochromatic terahertz (THz) difference frequency generation with organic crystal DSTMS was investigated experimentally. A double-pass KTiOPO4 optical parametric oscillator, pumped by a frequency-doubled Nd:YAG laser, was employed as the source of dual wavelength. The THz tuning spectrum covered a range of 0.88?19.27 THz. The dependence of the THz output on the crystal thickness and pump wavelength was studied. The results were well explained based on theoretical calculations. With a pump energy of 2.47 mJ, the output energy reached 85.3 nJ/pulse at 3.80 THz, which corresponded to a peak power of 17.9 W and photon conversion efficiency of .

Efficient Continuous-Wave 1053-nm Nd:GYSGG Laser With Passively Q-Switched Dual-Wavelength Operation for Terahertz Generation

Research on an efficient continuous-wave Nd:GYSGG laser at 1053 nm with excellent stability is demonstrated. The maximum output power is 4.17 W, corresponding to the conversion efficiency of 33.9% and the slope efficiency of 42.92%. Using a Cr:YAG absorber, pulsed dual-wavelength operation at 1053 and 1058.4 nm is obtained, of which the maximum single pulse energy and peak power are 172.1 μJ and 26.1 kW, respectively, when the pulse width is 6.6 ns and the repetition rate is 4.3 kHz. A polarization property is observed, owing to the anisotropy of Cr:YAG. This stably Q-switched dual-wavelength laser is a good pump source for the generation of a terahertz wave at 1.53 THz.

Remote Magnetic Field Sensor Based on Intracavity Absorption of Evanescent Field

In this paper, a remote magnetic field sensor based on intracavity absorption of evanescent field is experimentally demonstrated. A single-mode-no-core-single-mode (SNCS) fiber coated with magnetic fluid (MF) is inserted into a fiber ring laser through a circulator and a 3-dB coupler, and it works as the filter and sensing head simultaneously. As the light oscillates in the cavity of the fiber ring laser, intracavity absorption of the evanescent field will be induced in the interface of the no-core fiber and MF. We obtain a magnetic field sensor with a narrow 3-dB bandwidth that is less than 0.05 nm, a high signal-to-noise ratio ~40 dB, and magnetic sensitivity of 52.1 pm/mT and -0.3679 dBm/mT. Moreover, experiments show that it is convenient to achieve remote sensing by selecting different lengths of the transmission optical fiber connecting the circulator and 3-dB coupler, which has a slight impact on the sensitivity.

Coupled-Mode Theory for Cherenkov-Type Guided-Wave Terahertz Generation Via Cascaded Difference Frequency Generation

A scheme for monochromatic terahertz (THz) generation via cascading enhanced Cherenkov-type difference frequency generation (DFG) in a sandwich-like waveguide is proposed. The novel scheme has the potential to overcome the quantum-defect limit and to provide an efficient output coupling. This process is elucidated by developing a coupled-mode theory and taking into account the pump depletion, waveguide mode properties, and THz output coupling. The effect of cascading enhancement is analyzed by comparing with non-cascaded DFG situation. It is predicted that THz power can be boosted by nearly 8-fold with a 400 MW/cm2 pump in a 40-mm-long Si-LiNbO3-Si waveguide.

Propagation Characteristics of Two-Dimensional Photonic Crystals in the Terahertz Range

Based on plane wave expansion method, the band gaps of a two-dimensional terahertz photonic crystal with a square lattice are optimized through varying structural parameters. The electromagnetic field distribution is accurately described for a terahertz photonic crystal splitter by finite difference time domain method.

Widely tunable and monochromatic terahertz difference frequency generation with organic crystal 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile

We report an experimental study on widely tunable terahertz (THz) wave difference frequency generation (DFG) with hydrogen-bonded crystals 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1). The organic crystals were pumped by a ∼1.3 μm double-pass KTiOPO4 optical parametric oscillator. A tuning range of 0.02–20 THz was achieved. OH1 crystals offer a long effective interaction length (also high output) for the generation below 3 THz, owing to the low absorption and favorable phase-matching. The highest energy of 507 nJ/pulse was generated at 1.92 THz with a 1.89-mm-thick crystal. Comprehensive explanations were provided, on the basis of theoretical calculations. Cascading phenomenon during the DFG process was demonstrated. The photon conversion efficiency could reach 2.9%.