Simultaneous generation and Brillouin amplification of a dark hollow beam with a liquid-core optical fiber

We propose and demonstrate a new method to generate a dark hollow beam (DHB) and amplify it simultaneously by a liquid-core optical fiber (LCOF) filled with CS2. A DHB with an adjustable dark spot size (DSS) is simply obtained by changing the incident angle of the laser beam. Based on non-collinear Brillouin amplification, a weak DHB can be amplified with high gain. The amplification factor of 10(6) is achieved for a DHB of 4pJ. This DHB should have promising applications in many fields due to its compact structure, low cost, wide adjustment range of the DSS, and wide operating wavelength.