No abstract

In this Letter, we report on the experimental investigation of three-dimensional (3D) optical trapping by a tightly focused circular Airy beam (CAB). We compare the trapping strength of the beam for 800 nm polystyrene particles, with two equivalent Gaussian beams of the same envelope (SEGB) and the same spot-size (SSGB). Through video microscopy, we found that SEGB is incapable of forming a 3D trap, and particles are pushed along the beam propagation direction, while SSGB and CAB could form stable 3D traps. Measurements of trap stiffness revealed that although both beams have similar lateral trap stiffnesses, interestingly CAB has a 6.6-fold stronger axial trap, owning to its autofocusing nature. Furthermore, we found that trap stiffness at various trapping depths is nearly constant for CAB, in contrast with the Gaussian beam, implying that CAB is robust against spherical aberration.

The linear and nonlinear amplification features of an optical signal by a multimode class B laser have been discussed. The four-wave mixing process between the cavity central mode and the amplified input signal produces a sequence of satellite lines. It is demonstrated that short pulses can be formed by phase beating the satellite lines. In the linear regime, the laser amplifier acts like a three-mode free-running laser where the oscillations of two right and left adjacent modes are substituted by those of the amplified input signal and its image satellite line. In the nonlinear regime, two more symmetrical adjacent satellite lines are first added to the cavity electric field components and then the frequency of the cavity central mode is shifted towards the image satellite lines. At the same time, the number of central-mode photons is gradually decreased by raising the input signal strength. The central-mode photons are ultimately reduced to zero, where an injection-locking phenomenon takes place. Finally, we derive a heuristic conservation relation between the input energies to the laser by sum of the pumping and injected signals, and those distributed between the signal and image satellite lines and spontaneous emission radiation.