Jiahui Peng

Fourth-order dispersion mediated solitonic radiations in HC-PCF cladding

We observe experimentally, for the first time to our knowledge, the simultaneous emission of two strong conjugate resonant dispersive waves by optical solitons. The effect is observed in a small waveguiding glass feature within the cladding of a Kagome hollow-core photonic crystal fiber. We demonstrate theoretically that the phenomenon is attributed to the unusually high fourth-order dispersion coefficient of the waveguiding feature.

Control of energy deposition in femtosecond laser dielectric interactions

There are natural limits to the spatial resolution and the deposited energy densities that can be achieved in femtosecond laser dielectric modification. These arise because of the threshold-like nature of nonlinear absorption. We use two-pulse experiments to show that both limits can be exceeded by taking advantage of absorption seeded by free electrons or self-trapped excitons, depending on the pulse separation.

Femtosecond laser desorption of ultrathin polymer films from a dielectric surface

By focusing femtosecond pulses on the front and rear surface of a fused silica coverslip, we desorb 8-nm thick polymer films at submicron scale. To determine the role of the substrate in the desorption process, we measure the threshold for nonlinear absorption in fused silica and compare it to the threshold for desorption, taking into account the enhancement of the field at the dielectric-air interface. The results indicate that absorption of energy only occurs in the film. We then measure the beam radius in situ by the knife-edge technique and characterize the desorption by atomic force microscopy. The radius of the laser desorbed area is determined by the desorption threshold intensity and can be a factor of 5 smaller than the beam waist.

High-order dispersion-resulted tunable multiwavelength femtosecond laser.

Resonant dispersive waves generated by high-order dispersion in a Ti:sapphire mode-locked solitary laser are investigated and experiments are found to be in good agreement with theoretical analysis. Both theory and experiment show that the wavelength differences can be tuned in a large range via changing the cavity dispersion. This simple technique can be applied to the fields where tunable femtosecond pulses at multiple wavelengths are needed. The described mechanism may be applied in other systems where solitons are known to exist.

Carrier-envelope offset frequency measurement for tunable femtosecond lasers using resonant dispersive waves.

We report that carrier-envelope offset frequency measurement for tunable femtosecond lasers is fulfilled by directly using the resonant dispersive waves generated in a photonic crystal fiber.

Simple technique for spectral and temporal control of a mode-locked Ti:sapphire oscillator

We demonstrate a simple method to control the spectrum and to generate synchronized dual-wavelength pulses in a mode-locked Ti:sapphire laser by adjusting the cavity dispersion, without involving more complicated coupled cavities or two-slit systems. We explore the tunability range of our system, and demonstrate the possibility of obtaining pairs of synchronized pulses with adjustable frequency difference. Furthermore, we use this laser to obtain tri-wavelength pulses in the blue range of the spectrum, via second-order nonlinear processes in an LBO crystal. This system may become a useful tool for femtosecond coherent anti-Stokes Raman spectroscopy, and other applications as well.

16.7-TW laser system based on optical parametric chirped pulse amplification

A compact 16.7-TW/120-fs laser system based on optical parametric chirped pulse amplification is demonstrated. The chirped pulse was amplified from 50 pJ to 3.1 J. After compression, a final output pulse of 2.0 J/120 fs was obtained.A compact 3.6 TW/155 fs laser system based on optical parametric chirped pulse amplification is demonstrated. The system consists of a femtosecond Ti:sapphire oscillator, a pulse stretcher, a Nd:YAG/Nd:glass amplifier chain as pump laser, an OPA chain and a compressor. The pulses were amplified from 20 pJ to 900 mJ. After compression, a final output of 570 mJ/155 fs was obtained.

Epi-detected hybrid coherent Raman micro-spectroscopy

We demonstrate efficient epi-detected coherent Raman micro-spectroscopy using a simple laser system based on a femtosecond mode-locked oscillator. In our experiment, the non-resonant background is eliminated by using a hybrid technique, which combines laser pulse shaping and timing with frequency-resolved detection, and is based on the different temporal behavior of parametric and nonparametric processes. We perform careful analysis to make sure the coherent Raman-resonant signal is generated in the backward direction, and not forward-generated and then back-scattered. This demonstration may have important implications for coherent Raman microscopy.

Femtosecond laser desorption of thin polymer films from a dielectric surface

We desorb polymer films from fused silica with a femtosecond laser and characterize the results by atomic force microscopy. Our study as a function of beam geometry and energy reveals two ways of achieving spatially controlled nanodesorption.

Coherent Raman micro-spectroscopy with a mode-locked Ti:Sapphire oscillator

We demonstrate a simple, femtosecond-oscillator-based system for CARS microscopy, wherein impulsive Raman excitation is combined with narrow-band time-delayed, and therefore, background-free probing.