We present for the first time, to the best of our knowledge, a needle probe for photoacoustic viscoelasticity (PAVE) measurements at a depth of 1 cm below

We present for the first time, to the best of our knowledge, a needle probe for photoacoustic viscoelasticity (PAVE) measurements at a depth of 1 cm below the sample surface. The probe uses a gradient index rod lens, encased within a side-facing needle (0.7 mm outer diameter), to direct excitation light (532 nm) and detection light (1325 nm) focused on the sample, collecting and directing the returned detection light in a spectral domain low coherence interferometry system, which allows for obtaining optical phase differences due to photoacoustic oscillations. The feasibility of needle probe for PAVE depth characterization was investigated on gelatin phantoms and in vitro biological tissues. The experimental results in an in vivo animal model predict the great potential of this technique for in vivo tumor boundary detection.show less

By using a self-reference transfer oscillator method, two individual 1560 nm lasers with about 1.2 GHz frequency difference were phase locked to a 729 nm

By using a self-reference transfer oscillator method, two individual 1560 nm lasers with about 1.2 GHz frequency difference were phase locked to a 729 nm ultra-stable laser at two preset ratios. By measuring the beat frequency of the two 1560 nm lasers, fractional instabilities of 2×10-17 at 1 s and 2×10-20 at 10,000 s averaging time were obtained, and the relative offset compared with the theoretical value was 4.2×10-21±4.5×10-20. The frequency ratio of them was evaluated to a level of 1.3×10-20 in one day’s data acquisition. This work was a preparation for remote comparison of optical clocks through optical fiber links. The technique can also be used to synthesize ultra-stable lasers at other wavelengths.show less

The dispersive Fourier transform technique provides feasibility of exploring non-repetitive events and the buildup process in ultrafast lasers. In this pa

The dispersive Fourier transform technique provides feasibility of exploring non-repetitive events and the buildup process in ultrafast lasers. In this paper, we report a new buildup process of dissipative solitons in a simplified mode-locked Yb-doped fiber laser, which includes more complex physics stages such as the Q-switching stage, raised and damped relaxation oscillation stages, noise-like stage, successive soliton explosions stage, and soliton breathing stage. Complete evolution dynamics of noise-like pulse and double pulse are also investigated with dispersive Fourier transform. For the noise-like pulse dynamics process, it will only experience the Q-switching and relaxation oscillation stages. In the case of dissipative soliton and noise-like pulse, the double pulse buildup behavior is manifested as the replication of individual pulses. A weak energy migration occurs between two pulses before reaching steady state. Meanwhile, real-time mutual conversion of the dissipative soliton and noise-like pulse has been experimentally observed, which appears to be instantaneous without extra physical processes. To the best of our knowledge, this is the first report on these physical phenomena observed together in a mode-locked fiber laser. The results further enrich the dynamics of mode-locked fiber lasers and provide potential conditions for obtaining intelligent mode-locked lasers with controllable output.show less

In this research, the highly efficient external cavity feedback technology based on volume Bragg grating (VBG) is studied. By using the structure of a fas

In this research, the highly efficient external cavity feedback technology based on volume Bragg grating (VBG) is studied. By using the structure of a fast axis collimating lens, the beam transformation system, a slow axis collimating lens, and VBG, the divergence angle of the fast and slow axes of the diode laser incident on the VBG is reduced effectively, and the feedback efficiency of the external cavity is improved. Combined with beam combining technology, fiber coupling technology, and precision temperature control technology, a high-power and narrow-linewidth diode laser pump source of kilowatt class is realized for alkali metal vapor laser pumping. The core diameter of the optical fiber is 1000 µm, the numerical aperture is 0.22, the output power from the fiber is 1013 W, the fiber coupling efficiency exceeds 89%, and the external cavity efficiency exceeds 91%. The central wavelength is 852.052 nm (in air), which is tunable from 851.956 nm to 852.152 nm, and the spectral linewidth is 0.167 nm. Research results can be used for cesium alkali metal vapor laser pumping.show less