Jinping He

Diode pumped passively mode-locked Yb:SSO laser with 2. 3ps duration

This paper reports on a diode-pumped picosecond passively mode-locked Yb:SSO laser. Pulses as short as 2.3 ps with a repetition rate of 53 MHz were generated, without extra negative dispersion elements. The output power achieved 1.87 W at a pump power of 11.5 W. Continuous-wave operation and wavelength tuning were examined. The CW operation achieved 3.55 W output power with a slope efficiency of 44.5%; its tuning can cover the range of 1034.0-1089.7 nm.

Biological imaging with nonlinear photothermal microscopy using a compact supercontinuum fiber laser source.

Nonlinear photothermal microscopy is applied in the imaging of biological tissues stained with chlorophyll and hematoxylin. Experimental results show that this type of organic molecules, which absorb light but transform dominant part of the absorbed energy into heat, may be ideal probes for photothermal imaging without photochemical toxicity. Picosecond pump and probe pulses, with central wavelengths of 488 and 632 nm, respectively, are spectrally filtered from a compact supercontinuum fiber laser source. Based on the light source, a compact and sensitive super-resolution imaging system is constructed. Further more, the imaging system is much less affected by thermal blurring than photothermal microscopes with continuous-wave light sources. The spatial resolution of nonlinear photothermal microscopy is ~ 188 nm. It is ~ 23% higher than commonly utilized linear photothermal microscopy experimentally and ~43% than conventional optical microscopy theoretically. The nonlinear photothermal imaging technology can be used in the evaluation of biological tissues with high-resolution and contrast.

Noninvasive, label-free, three-dimensional imaging of melanoma with confocal photothermal microscopy: Differentiate malignant melanoma from benign tumor tissue

Skin cancer is one of the most common cancers. Melanoma accounts for less than 2% of skin cancer cases but causes a large majority of skin cancer deaths. Early detection of malignant melanoma remains the key factor in saving lives. However, the melanoma diagnosis is still clinically challenging. Here, we developed a confocal photothermal microscope for noninvasive, label-free, three-dimensional imaging of melanoma. The axial resolution of confocal photothermal microscope is ~3 times higher than that of commonly used photothermal microscope. Three-dimensional microscopic distribution of melanin in pigmented lesions of mouse skin is obtained directly with this setup. Classic morphometric and fractal analysis of sixteen 3D images (eight for benign melanoma and eight for malignant) showed a capability of pathology of melanoma: melanin density and size become larger during the melanoma growth, and the melanin distribution also becomes more chaotic and unregulated. The results suggested new options for monitoring the melanoma growth and also for the melanoma diagnosis.

Generation of sub-20-fs deep-ultraviolet pulses by using chirped-pulse four-wave mixing in CaF2 plate.

Sub-20-fs deep ultraviolet (DUV) pulses are generated by using nondegenerate, chirped-pulse four-wave mixing of the fundamental and second-harmonic pulses from a commercial Ti:sapphire amplifier in a CaF(2) plate. The energy of the DUV pulses is 3.8 μJ, with a conversion efficiency from total pump energy to DUV of ~3.8%. The DUV pulse is compressed using a pre-chirp, introduced via a fused silica window in the fundamental beam. The central wavelength of the DUV spectrum can be tuned from 257 to 277 nm by adjusting the cross angle between the two pump beams. The spectrum can reach a width of 16.8 nm, which can support a pulse duration of 8.7 fs.

Low threshold, high power passively mode-locked Yb:SSO laser

We reports on a diode-pumped passively mode-locked Yb:SSO laser with a SESAM. Pulses duration as short as ~2 ps with a repetition rate of 53 MHz were generated. The output power achieved ~1.9 W at a pump power of 11.5 W.

Generation of stable two-color laser pulses in photonic crystal fiber for microscopy

We have generated two-color laser pulses in the visible range from a photonic crystal fiber pumped with a femtosecond Ti:sapphire oscillator. The central wavelengths of the two peaks are 564 and 644 nm with the tunable range of about 10 nm by adjusting the pump intensity. The average power of each peak is higher than 1 mW and the rms stability is 1.3%, which is nearly the same as the pump laser. The most probable mechanism of the formation of the two-color pulses is high-order soliton fission. The two-color femtosecond pulses are useful in microscopy.

Stable, efficient diode-pumped femtosecond Yb:KGW laser through optimization of energy density on SESAM

An efficient high-power diode-pumped femtosecond Yb:KGW laser is repored. Through optimization of energy density by semiconductor saturable absorber mirror, output power achieved 2.4 W with pulse duration of 350 fs and repetition rate of 53 MHz at a pump power of 12.5 W, corresponding to an optical-to-optical efficiency of 19.2%. We believe that it is the highest optical-to-optical efficiency for single-diode-pumped bulk Yb:KGW femtosecond lasers to date.

High-power picosecond regenerative amplifier based on CW diode side-pumped Nd:YAG with high beam quality

A compact high-power picosecond regenerative amplifier based on continuous wave (CW) diode side-pumped Nd:YAG is demonstrated. Average power of 8.8 W is achieved at a repetition rate of 5 kHz at a wavelength of 1 064 nm with a pulse duration of 28 ps, corresponding to a pulse energy of 1.76 mJ and a peak power of 62.9 MW. The beam quality is close to the diffraction limit with M2x = 1.24, M2y =1.03. To the best of our knowledge, this is the highest pulse energy obtained from a CW diode pumped Nd:YAG picosecond regenerative amplifier.

Super-resolution imaging via aperture modulation and intensity extrapolation

High-resolution telescopic imaging is of great importance in astronomy. Compared to the complexity and huge cost of constructing extremely-large telescopes, super-resolution technique which breaks the diffraction limit of the imaging system can enhance the spatial resolution with compact setup and low cost. In this paper, a novel super-resolution telescopic imaging method based on aperture modulation and intensity extrapolation is demonstrated, with both simulated and experimental studies performed. The simulation results show that the method can enhance the resolving power of a diffraction-limited telescopic imaging system by >5 times in noise-free case, and the improvement still reaches ~1.8 times with a signal-to-noise ratio of only ~10. The preliminary experimental results show a resolution enhancement of ~1.36 times for the limitations of the experimental setup. Better performance is possible with the images for reconstruction denoised and registered more precisely. The method is also useful in wide-field microscopy.

Mechanism study of 2-D laser array generation in a YAG crystal plate

We have reproduced the process of two-dimensional array generation by using two crossing laser beams in a YAG crystal plate based on numerical simulation considering cross-phase modulation (XPM) and self-focusing. Furthermore, we come to the conclusion that both XPM and the cylindrical symmetry breaking in the initial beam profile contributes to the generation of two-dimensional array. In addition, we have studied the threshold input laser beam power for the two crossing beams splitting in a YAG crystal plate. Our study could be valuable in various applications, such as 2-D all-optical switching devices or multicolor pump-probe experiments.