Chao Tan

Dressed dynamics of two time-reversed shapes of Airy pulses in a relaxing nonlinear medium

We investigate the dressed dynamics of two kinds of asymmetric Airy pulses with time-reversed shapes in a relaxing nonlinear medium. Airy tails act as low intensity “dressing” pulses, refuel the Airy main lobe, and modify propagation dynamics of Airy pulses. It is demonstrated that a soliton sheds from the main lobe of Airy pulses and the spectrum maximum intensity is periodically manifested due to the effect of self-phase modulation. The intrinsically asymmetric nature of Airy pulses is revealed through the nonlinear generation of a Raman soliton self-frequency shift and the generation of static solitons driven by the soliton fission processes and the interactions with dressing Airy tails. The resulting Raman-induced frequency shift can be controlled by using time-reversed Airy pulses and varying truncation coefficients. Numerical results show that the frequency shift can be enhanced with a larger input peak power as well.

Generation of ring-shaped beams by a graded-index plasma lens

We experimentally demonstrate the generation of ring-shaped beams using a plasma channel with Gaussian profile. The plasma channel is produced when an intense femtosecond pulse propagates in carbon disulfide. The refractive index of the plasma is similar to that of a graded-index lens. Due to the existence of critical plasma density, the beam from the He–Ne laser cannot pass through the center region of the plasma and is refracted in the periphery. The dark spot size of the ring-shaped beams can be controlled easily by a femtosecond pulse. We also show the propagation of ring-shaped beams in free space.

Reversible conversion between optical frequencies of probe and idler waves in regime of optical event horizon

The controlling optical frequency in the regime of an optical event horizon by the collision between a soliton and a probe pulse is investigated, and the process by which the probe is converted into the generated pulse (idler) with new optical frequency is reversible. For the two cases in which the probe wave interacts with a bright/dark soliton, a unified analytical formula governing the reversible frequency conversion process is derived that can predict the frequency of the idler very well. This reversible frequency-conversion process is validated by cascaded four-wave mixing (FWM) triggered by a set of quasi-CW fields, strongly suggesting that the process arose from cascaded Bragg scattering. It establishes a link between the nonlinear interactions of a soliton with the probe and FWM of monochromatic quasi-CWs.

Plasma optical modulation for lasers based on the plasma induced by femtosecond pulses

We present a theoretical and experimental study of plasma optical modulation for probe lasers based on the plasma induced by pump pulses. This concept relies on two co-propagating laser pulses in carbon disulfide, where a drive laser pulse first excites plasma channels while a following carrier laser pulse is modulated by the plasma. The modulation on the probe beam can be conveniently adjusted through electron density, plasma width, propagation distance of plasma, the power of pump lasers, or the pump beams profile. The experimental results and theoretical solutions are very consistent, which fully illustrates that this method for plasma optical modulation is reasonable. This pump-probe method is also a potential measurement technique for inferring the on-axis plasma density shape.

A Method for Measuring the Pulsewidth at Different Spatial Positions of Ultrashort Laser Pulses

In this letter, we propose a method for measuring the pulsewidths at different spatial positions of ultrashort laser pulses. By measuring the pulsewidths varying with spatial positions of chirped and chirped-free femtosecond laser pulses, it is found that pulsewidths at edge positions are longer than that of central positions due to the effect of residual spatial chirp. Then, we measure the temporal evolutions of pulse at the strongest spatial modulation position after small-scale self-focusing and our results show that the pulsewidths become narrower with increasing spatial contrast due to spatiotemporal coupling effect. We find that the method is reliable and feasible.

All-Optical Switching Based on the Plasma Channel Induced by Laser Pulses

We display a theoretical and experimental study of all-optical switching for signal lasers based on the plasma channel induced by the control laser. Using the plasma channel generated in the carbon disulfide (CS2) solution, the signal light can be modulated as some spatial distributions including unchanging, ring-shaped beam, and other intensity profiles. The modulation on the signal light can be conveniently adjusted by changing the control light’s incident intensity distribution. We can infer the dark spot shape in the modulated signal laser through the intensity profile of control laser beam. These results provide the great potential of plasma channel induced by lasers as an all-optical switching for various optoelectronic applications.

Experimental realization of spatial light modulation based on graded-index plasma channels

Abstract. We experimentally demonstrate spatial light modulation based on graded-index plasma channels induced by femtosecond pulses. The spatial profile of the probe beam can be conveniently controlled by adjusting the intensity distribution of the pump beam or by changing the relative position between pump beam and probe beam. We also show that the modulation depth of the probe beam can be controlled by adjusting the power of the pump beam.

Graphene Oxide: A Perfect Material for Spatial Light Modulation Based on Plasma Channels

The graphene oxide (GO) is successfully prepared from a purified natural graphite through a pressurized oxidation method. We experimentally demonstrate that GO as an optical media can be used for spatial light modulation based on plasma channels induced by femtosecond pulses. The modulated beam exhibits good propagation properties in free space. It is easy to realize the spatial modulation on the probe beam at a high concentration of GO dispersion solutions, high power and smaller pulse width of the pump beam. We also find that the spatial modulation on the probe beam can be conveniently adjusted through the power and pulse width of pump lasers, dispersion solution concentration.

An experimental method for pulse-width measurement in partial positions of an ultrashort-pulsed beam

We experimentally show a method for pulse-width measurement. Pulse widths at different partial positions of an ultrashort-pulsed beam are measured, results show that pulse widths in the center of the beam are less than that of in the edge because of the existence of residual chirp. We also investigate the temporal evolution at a strongest spatial modulation position of the beam during small-scale self-focusing, it finds that its pulse width decreases as power increases due to a spatiotemporal coupling effect. We find that this method not only can be used to accurately measure the pulse width at any one spatial position of the beam, but also be useful for real-time monitoring of spatial-temporal evolution.