Huadong Lu

Physical conditions of single-longitudinal-mode operation for high-power all-solid-state lasers

The optimal physical conditions of single-longitudinal-mode (SLM) operation for continuous-wave all-solid-state lasers with high output powers are investigated theoretically and experimentally. The dependence of the operation conditions on the linear and nonlinear intracavity losses of the laser is numerically calculated. The theoretical analysis is demonstrated by the experimental measurements on a home-made Nd:YVO4 laser. The stable SLM output up to 33.7 W with optical-optical conversion efficiency of 44.9% at 1064 nm wavelength is recorded for over 7 h. The experimental results are in good agreement with the theoretical expectation.

Single frequency Ti:sapphire laser with continuous frequency-tuning and low intensity noise by means of the additional intracavity nonlinear loss

A single frequency Ti:sapphire (Ti:S) laser with continuous frequency-tuning and low intensity noise is presented, in which an extra nonlinear (NL) loss crystal is placed inside the resonator instead of the traditional etalon locking system. When a NL crystal is inserted into a home-made Ti:S laser resonator, the single frequency laser of 1.27 W at 795 nm with a continuous frequency-tuning range of 48 GHz is realized under the pump level of 11.27 W and the intensity noise at the lower frequencies is successfully suppressed.

Comparative study of the frequency-doubling performance on ring and linear cavity at short wavelength region.

We theoretically and experimentally perform a comparative study on performance of the linear standing-wave cavity and ring cavity for external cavity frequency doubling at the wavelength from 795 nm to 397.5 nm. The two cavities show obvious differences of the thermal effect of nonlinear crystal, cavity sensitivity, and maximum output power. The results show that ring cavity as the external enhancement cavity is a better choice than standing-wave cavity at short wavelength region. At last, a 397.5 nm violet laser with 408 mW corresponding to an input power of 992 mW is obtained by using the ring cavity, considering the original mode-matching efficiency of 98% between the 795 nm laser and frequency doubling cavity, the conversion efficiency is 41.9%.

Investigation of the thermal lens effect of the TGG crystal in high-power frequency-doubled laser with single frequency operation

The thermal lens effect of the TGG crystal is investigated theoretically and experimentally. The theoretical analysis is demonstrated by the experimental measurements on a home-made frequency-doubled Nd:YVO(4) laser with single-frequency operation. In the presence of the thermal lens effect of the TGG crystal, the output power can be optimized by shortening the distance between the cavity mirrors of M(3) and M(4) (two plane-concave mirrors placed at two sides of the second-harmonic generator). Consequently, a single-frequency laser with output power of 18.7 W at 532 nm is obtained. The power stability and the beam quality M(2) are better than ±0.4% for 5 hours and 1.08, respectively. Meanwhile, we observe and discuss a bistability-like phenomenon of the laser in the cases of increasing and decreasing the incident pump power.

Broadband tunable single-frequency Nd:YVO4/LBO green laser with high output power

We present a diode-pumped broadband tunable single-frequency and frequency-doubling Nd:YVO4/LBO laser with high output power of 10.5 W in all tuning ranges around 532 nm. An etalon placed inside the resonator and the laser gain medium in a wedge shape are used for the coarse- and fine-tuning elements, respectively. By independently scanning the temperatures of the two tuning elements, broadband tunable ranges of 12 and 24 GHz have been achieved, respectively, for the fundamental and the second-harmonic waves.

Four watt long-term stable intracavity frequency-doubling Nd:YVO(4) laser of single-frequency operation pumped by a fiber-coupled laser diode.

The longitudinal-mode stability of a single-frequency intracavity frequency-doubling laser can be enhanced by increasing the ratio between the nonlinear spectral bandwidth and the gain bandwidth of the laser. A 4 W long-term stable cw single-frequency green laser is obtained using an etalon inside the laser cavity as a spectral filter. No mode hopping is observed when the laser operates for 6 h and the power fluctuation is less than +/-1.2%. In contrast, in the situation of no etalon inside the laser cavity, mode hopping can be observed at irregular intervals and the power fluctuation is +/-3.8% when the laser operates for 4 h.

Continuous-wave single-frequency laser with dual wavelength at 1064 and 532 nm

A continuous-wave high-power single-frequency laser with dual-wavelength output at 1064 and 532 nm is presented. The dependencies of the output power on the transmission of the output coupler and the phase-matching temperature of the LiB(3)O(5) (LBO) crystal are studied. An output coupler with transmission of 19% is used, and the temperature of LBO is controlled to the optimal phase-matching temperature of 422 K; measured maximal output powers of 33.7 W at 1064 nm and of 1.13 W at 532 nm are obtained with optical-optical conversion efficiency of 45.6%. The laser can be single-frequency operated stably and mode-hop-free, and the measured frequency drift is less than 15 MHz in 1 min. The measured Mx2 and My2 for the 1064 nm laser are 1.06 and 1.09, respectively. The measured Mx2 and My2 for the 532 nm laser are 1.12 and 1.11, respectively.

High power single-frequency and frequency-doubled laser with active compensation for the thermal lens effect of terbium gallium garnet crystal.

The thermal lens effect of terbium gallium garnet (TGG) crystal in a high power single-frequency laser severely limits the output power and the beam quality of the laser. By inserting a potassium dideuterium phosphate (DKDP) slice with negative thermo-optical coefficient into the laser resonator, the harmful influence of the thermal lens effect of the TGG crystal can be effectively mitigated. Using this method, the stable range of the laser is broadened, the bistability phenomenon of the laser during the process of changing the pump power is completely eliminated, the highest output power of an all-solid-state continuous-wave intracavity-frequency-doubling single-frequency laser at 532 nm is enhanced to 30.2 W, and the beam quality of the laser is significantly improved.

Generation of high-power single-frequency 397.5 nm laser with long lifetime and perfect beam quality in an external enhancement-cavity with MgO-doped PPSLT.

Continuous-wave single-frequency high power 397.5 nm laser with long lifetime and perfect beam quality is one of the essential resource to generate the squeezed and entanglement states of optical beams resonant with D1 line of Rubidium atoms at 795 nm. In this paper, We present the experimental generation of single-frequency high power 397.5 nm ultra-violet (UV) laser with long lifetime and perfect beam quality by using periodically poled MgO-doped stoichiometric lithium tantalate (MgO:PPSLT) crystal as the frequency doubler in an external enhancement ring cavity. When the transmission of the input coupler is 5.5%, the maximal output power of single-frequency 397.5 nm UV laser of 407 mW is obtained under the incident pump power of 1.9 W with the corresponding conversion efficiency of 22.8%. When the output power is 290 mW, the measured power stability and the beam quality are lower than 0.28% and 1.02, respectively. Moreover, any damage is not observed in our experiment which lasts about 1 year.

Intensity noise manipulation of a single-frequency laser with high output power by intracavity nonlinear loss.

The influences of intracavity nonlinear losses on the intensity noise of output lasers are theoretically and experimentally investigated with an all-solid-state single-frequency laser with high gain. By means of tuning the temperature of a nonlinear crystal deliberately placed inside the laser resonator, the intracavity nonlinear loss of the laser is controlled. The dependence of the frequency and amplitude of the resonant relaxation oscillation peak on the nonlinear loss is studied in detail for both fundamental-wave (FW) and second-harmonic-wave (SHW). We find that, by controlling the temperature of the nonlinear crystal, the intensity noises of the laser can be transferred between FW and SHW. The theoretical predictions are in good agreement with the experimental measurements. The obtained results can be applied to manipulate and suppress the laser noises.