Interaction of light filaments in air

This paper analytically investigates the interaction of light filaments generated by a femtosecond laser beam in air. It obtains the Hamiltonian of a total laser field and interaction force between two filaments with different phase shifts and crossing angles. The property of the interaction force, which leads the attraction or repulsion of filaments, is basically dependent on the phase shift between filaments. The crossing angle between two filaments can only determine the magnitude of the interaction force, but does not change the property of the force.

Forward acceleration and generation of femtosecond megaelectronvolt electron beams by an ultrafast intense laser pulse

We present a new mechanism of energy gain of electrons accelerated by a laser pulse. It is shown that when the intensity of an Tiltrafast intense laser pulse decreases rapidly along the direction of propagation, electrons leaving the pulse experience an action of ponderomotive deceleration at the descending part of a lower-intensity laser field than acceleration at the ascending part of a high-intensity field, thus gain net energy from the pulse and move directly forward. By means of such a mechanism, a megaelectronvolt electron beam with a bunch length shorter than 100 fs could be realized with an ultrafast (≤30 fs), intense (≥1019 W/cm2) laser pulse.

Femtosecond laser highly-efficient plane processing based on an axicon-generated donut-shaped beam

A simple technique is proposed for highly-efficient plane processing fully based on femtosecond laser beam shaping. The laser intensity distribution is transformed from a Gaussian to a donut shape. As the donut-shaped focus seems like a flat top from the side view, a plane with a high level of flatness is obtained directly by scanning once. By applying it to polishing experiments, the surface roughness can be improved significantly. The influence of scanning speed, laser pulse energy, and scanning times on the roughness is also discussed. Moreover, the scanning width can be flexibly controlled in a wide range.

Rapid fabrication of reconfigurable helical microswimmers with environmentally adaptive locomotion

Artificial helical microswimmers with shape-morphing capacities and adaptive locomotion have great potential for precision medicine and noninvasive surgery.However,current reconfigurable helical microswimmers are hampered by their low-throughput fabrication and limited adaptive locomotion.Here,a rotary holographic processing strategy(a helical femtosecond laser beam)is proposed to produce stimuli-responsive helical microswimmers(<100μm)rapidly(<1 s).This method allows for the easy one-step fabrication of various microswimmers with controllable sizes and diverse bioinspired morphologies,including spirulina-,Escherichia-,sperm-,and Trypanosoma-like shapes.Owing to their shape-morphing capability,the helical microswimmers undergo a dynamic transition between tumbling and corkscrewing motions under a constant rotating magnetic field.By exploiting adaptive locomotion,helical microswimmers can navigate complex terrain and achieve targeted drug delivery.Hence,these microswimmers hold considerable promise for diverse precision treatments and biomedical applications.

RF gun for an intense THz radiation source

A new facility is under construction at the Shanghai Institute of Applied Physics, to generate femto-second electron bunches and intense coherent THz radiation pulses. A thermionic RF-gun is used to be the electron source of the linac, which is 1.6 cell, π/2, side coupled in design. In the following of this paper, the design, manufacture and beam operation of this gun are presented.