Abstract

Radially polarized laser beams are advantageous for several applications, such as laser cutting, trapping of micron-sized metallic particles, or vacuum acceleration of electrons. In laser cutting of metals, the radial polarisation ensures that the electric field vector is always perpendicular to the cutting front irrespective of the direction of cutting and thus the overall efficiency may double [1]. Radial polarisation is also predicted to be useful in trapping of metallic particles. It is possible to trap metallic micro-particles in three dimensions by using strongly focused, radially polarized laser beams [2]. Lastly, radially polarized laser beams may find application in accelerating electrons to relativistic energies. Such a scheme, however, requires highly efficient, high power, short pulse lasers with radial polarisation [3] which currently do not exist. Recently, we have demonstrated that by exploiting the specific properties of the thermally induced refractive index changes in the laser active medium it is possible to modify the stability of a laser oscillator such that its preferred state of polarisation is radial. Later we have extended this scheme towards Q-switched laser systems. Here, we present results demonstrating that the same scheme can even be applied to mode-locked laser operation which we believe will be an important step towards high-intensity applications.

© 2009 IEEE