Kuanshou Zhang

Generation of a squeezing vacuum at a telecommunication wavelength with periodically poled LiNbO3

A continuous-wave squeezed vacuum at a telecommunication wavelength was reported. Using an Er-doped fiber amplifier seeded by a single-frequency laser diode as the pump laser source, via a frequency doubler and an optical parametric oscillator based on periodically poled LiNbO3, the squeezed vacuum of 2.4±0.1dB below the shot noise limit at 1560nm was observed (the inferred initial squeezing is about 6.4±0.5dB). This system is compatible with standard telecommunication optical fiber, and will be useful for long-distance quantum communication and distributed quantum computing.

Stable continuous-wave single-frequency Nd:YAG blue laser at 473 nm considering the influence of the energy-transfer upconversion

We report a continuous-wave (cw) single frequency Nd:YAG blue laser at 473 nm end-pumped by a laser diode. A ring laser resonator was designed, the frequency doubling efficiency and the length of nonlinear crystal were optimized based on the investigation of the influence of the frequency doubling efficiency on the thermal lensing effect induced by energy-transfer upconversion. By intracavity frequency doubling with PPKTP crystal, an output power of 1 W all-solid-state cw blue laser of single-frequency operation was achieved. The stability of the blue output power was better than +/- 1.8% in the given four hours.

Diode-end-pumped continuous-wave Nd:YAG laser at 946 nm of single-frequency operation

We report a diode-end-pumped continuous-wave (CW) Nd:YAG laser at 946 nm of single frequency operation. A ring laser resonator was designed and the output coupler transmission was optimized based on the investigation of the influence of the output coupler transmission on the thermal lens effect induced by energy-transfer upconversion. A maximum output power of 1.5 W CW single-frequency laser at 946 nm was achieved. The stability of the laser output power was better than ±1% in the given four hours.

400 mW low noise continuous-wave single-frequency Er,Yb:YAl 3 (BO 3 ) 4 laser at 1.55 μm

We build up a LD end-pumped Er,Yb:YAB laser at 1.55 μm and improve the laser performance by end cooling the gain medium efficiently through a sapphire plate. 680 mW cw single transverse mode laser output was obtained with the slope efficiency of 16.3%. Using an etalon placed in the laser cavity, 400 mW cw single frequency 1.55 μm laser output was achieved with the slope efficiency of 11.8%. The laser power fluctuation was less than ± 1.3% in a given period of 1.5 hours. The 1.55 μm laser presents low noise properties, that the intensity and the phase noise reach the shot noise level for the analysis frequencies higher than 4 MHz and 5 MHz, respectively.

Noise suppression, linewidth narrowing of a master oscillator power amplifier at 1.56μm and the second harmonic generation output at 780nm

We have demonstrated a 2 W cw single frequency 1.56 microm laser using a diode laser seeded Erbium doped fiber power amplifier, and a 715 mW cw single-frequency 780 nm laser by an external cavity enhanced second-harmonic-generation. The performance of the system was improved greatly by the seed diode laser optical locked to the resonant frequency of confocal F-P cavity. The linewidth of the 1.56 microm laser was narrowed from 2 MHz to 200 kHz, meanwhile, the intensity and phase noises were suppressed by 10 dB and 12 dB, respectively. The linewidth of the 780 nm laser was narrowed from 2 MHz to 300 kHz, meanwhile, the intensity and phase noises were suppressed by 11 dB and 13 dB, respectively.

High-efficiency generation of a continuous-wave single-frequency 780 nm laser by external-cavity frequency doubling

We demonstrated a 670 mW continuous-wave single-frequency laser source at 780 nm by using external-cavity-enhanced second-harmonic generation of a seeded fiber amplifier in periodically poled lithium niobate. A maximum second-harmonic conversion efficiency of 58% was achieved. The source can work stably over 1 h by locking the frequency-doubling cavity, while the power stability is less than 2%.

Investigation of the characteristics of the intensity noise of singly resonant active second-harmonic generation

We derive analytical expressions for the quantum-noise spectra of a singly resonant active frequency-doubling laser with single-frequency operation by using a linearized input–output method. For operation of a practical solid-state laser, we analyze separately the contributions of the various noise sources to the final spectrum. The change in resonance in the spectrum from an overdamped- (at higher μ) to an underdamped- (at smaller μ) driven second-order oscillator where μ is the nonlinear coupling coefficient, was experimentally observed with a diode-pumped Nd:YVO4+KTP single-frequency-doubling laser. The experimental result is in good agreement with the theoretical expectation.

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.

Quantum correlation between fundamental and second-harmonic fields via second-harmonic generation

We experimentally demonstrated the quantum anticorrelation between fundamental (1064 nm) and second-harmonic (532 nm) fields in an external cavity-enhanced singly resonant periodically poled KTP (PPKTP) frequency doubler. Fundamental amplitude squeezing of 0.5 dB and second-harmonic amplitude squeezing of 0.3 dB were generated simultaneously at a pump power of 6.1 mW. Meanwhile, quantum anticorrelation of 0.64 dB between the squeezed fundamental and the second-harmonic fields was observed.

Stable, 12 W, continuous-wave single-frequency Nd:YVO 4 green laser polarized and dual-end pumped at 880 nm

Based on a polarized and dual-end pumping scheme and a ring resonator, a stable, high power and high beam quality continuous-wave single-frequency Nd:YVO4 green laser directly pumped at 880 nm has been fabricated. A measured maximum output power of 12 W at 532 nm was obtained with a conversion efficiency of 23.1%. The stability of the output was better than ±0.5% and no mode hopping was observed over a period of five hours. The output beam was almost diffraction limited with a measured beam quality of M2(x)=1.03 and M2(y)=1.02. The intensity noise reached the shot noise limit (SNL) for analysis frequencies above 3.5 MHz, and the phase noise was 1.3 dB above the SNL in the range of 2 to 20 MHz.