Zhongxing Jiao

High average power 2 μm generation using an intracavity PPMgLN optical parametric oscillator

An intracavity quasi-phase-matched optical parametric oscillator (OPO) has been developed for the purpose of generating radiation with high average power and high repetition rate in the 2 μm regime. The device is a degenerate OPO based on a 3 mm thick MgO-doped periodically poled LiNbO(3) (PPMgLN) crystal, which is pumped in turn within the cavity by a diode side-pumped, Q-switched 1 μm Nd:YAG laser operating at 10 kHz. Up to 20 W broadband 2 μm radiation can be generated with a compact configuration under the crystal temperature of 115 °C. The beam profile is close to circularly symmetric with M(2) ~ 10.

Evolution of spin coherence dynamics and g factor with electron excess energy in bulk intrinsic GaAs

Circularly polarized absorption quantum-beat spectroscopy is used to study excess-energy dependence of electron-spin coherence dynamics in intrinsic GaAs. Absorption quantum beats are observed. The quantum-beat oscillatory frequency is used as a high precision measure of electron g factor. Double linear energy dependence of g factor is obtained and disagrees with the prediction of k∙p theory. A theoretical calculation reveals the double linear energy dependence reflects the energy dependence of g factor of electrons measured through light-hole- and heavy-hole-electron transitions, respectively. The phase of the quantum beats provides the key information to distinguish the two transitions experimentally.

Temperature dependence of electron-spin coherence in intrinsic bulk GaAs

Temperature dependence of electron-spin coherence dynamics is investigated for an intrinsic bulk GaAs in the Voigt geometry using the elliptically polarized absorption quantum-beat spectroscopy. Temperature dependences of spin coherence and recombination lifetimes as well as g factor of electrons are reported over a temperature range from 8.1to260K. The temperature dependence of spin coherence lifetime (T2*) agrees well with a reported theoretical calculation and can be fitted well by a relationship T2*∼T−1∕2, which provides an evidence to support electron-spin decoherence dominated by the Bir-Aronov-Pikus mechanism. The temperature dependence of g factor also agrees well with reported results.

Generation of radially polarized beams based on thermal analysis of a working cavity

The laser oscillation and polarization behavior of a side-pumped Nd:YAG laser are studied theoretically and experimentally by a thermal model for a working cavity. We use this model along with the Magni method, which gives a new stability diagram, to show important characteristics of the resonator. High-power radially and azimuthally polarized laser beams are obtained with a Nd:YAG module in a plano-plano cavity. Special regions and thermal hysteresis loops are observed in the experiments, which are concordant with the theoretical predictions.

Elliptically polarized absorption spectroscopy and observation of spin coherence in intrinsic GaAs

The elliptically polarized absorption spectroscopy is further developed to observe electron spin coherence dynamics in an intrinsic bulk GaAs in Voigt geometry. Absorption saturation quantum beats are observed and explained as spin-precession-dependent state filling. An analytical model is developed quantitatively to describe the quantum beats and used to fit experimental data to retrieve spin coherence lifetime. Comparing to the reported data reveals that the spin coherence dynamics of the real and imaginary of a complex refractive index is much different.

High-efficiency near-degenerate PPMgLN optical parametric oscillator with a volume Bragg grating

We demonstrate a high-efficiency near-degenerate periodically poled MgO:LiNbO(3) (PPMgLN) optical parametric oscillator (OPO) using a volume Bragg grating (VBG) output coupler (OC) pumped by a multilongitudinal Q-switched Nd:YVO(4) laser at 20 kHz repetition rate. A total parametric power of 4.3 W with a conversion efficiency of 60% is achieved in a double-pass pump configuration. The output power improvement over the case of a single-pass pump is nearly 60%. Both the signal and the idler bandwidths are less than 40 GHz and are confined within 170 GHz bandwidth at 2128.8 nm. Such efficiency is, to our knowledge, the highest ever achieved from a degenerate OPO using a VBG OC.

Compact Efficient 2.1-

We present a compact efficient intracavity MgO:PPLN optical parametric oscillator (OPO) with a volume Bragg grating output coupler pumped by a Q-switched Nd:YVO4 laser operating in 2.1-μm region. Narrowband 2.1-μm output power of 3.7 W is achieved with a pulse duration <;2 ns at 15-kHz repetition rate. A maximum conversion efficiency of 19.5% from laser diode (LD) to 2.1 μm is obtained at 17.5-W LD pump power. The 2.1-μm beam quality factors M2 of 1.85 and 2.37 in horizontal and vertical directions are obtained. To the best of our knowledge, the efficiency is the highest ever achieved from an intracavity OPO in 2-μm region.

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The cavity dispersion noncoaxiality (CDN) effects on broadband few-cycle pulse generation of a Kerr-lens mode-locked Ti:sapphire laser is investigated theoretically and experimentally. It is found that the influence of CDN is comparable with that of self-focusing and self-phase-modulation in the frequency-dependent mode size (FDMS) effects. Spectra extending from 680 nm to 1020 nm with pulse duration shorter than three optical cycles are favorably generated under the minimum CDN in the vicinity of the coaxial point of the sub-cavity.

m Intracavity MgO:PPLN OPO With a VBG Output Coupler

A high average-power 2 μm laser with good beam quality based on an intracavity potassium titanium oxide phosphate (KTP) optical parametric oscillator (OPO) is demonstrated. A concave lens is used in the 1064 nm Nd:YAG pumped laser cavity to compensate for the thermal lensing of the laser rod. The cavity length of the KTP OPO is enlarged to improve the 2 μm beam quality. The maximum average output of the 2 μm laser is up to 18 W at 7 kHz with M 2 less than 6 and pulse width of 70 ns. The FWHM of the signal and idle lights are both less than 3 nm.

The cavity dispersion noncoaxiality effects on broadband few-cycle pulse generation in Ti:sapphire laser

A continuous-wave singly resonant optical parametric oscillator employing a volume Bragg grating as one of the end mirrors is demonstrated. Due to the high intracavity power, the minute absorption of the grating leads to the thermal induced surface deformation and reflection peak shift. In this letter, the former effect is confirmed to be a cause of beam quality degradation of the resonant signal, while the latter, together with the thermal effects of the nonlinear crystal, leads to unconventional behaviors of power and stability. To the best of our knowledge, the joint effects of the grating and the nonlinear crystal are studied for the first time in details by changing the thermal effects of grating in varied strengths.