Generation of controllable Ince–Gaussian modes in a passively Q-switched microchip laser under truncated decentred Gaussian beam pumping

We report a passively Q-switched (PQS) Nd : YAG/Cr⁴⁺ : YAG microchip laser pumped by a truncated decentred Gaussian beam for controllable Ince–Gaussian (IG) mode generation. IG^e(n, n) modes (n = 0, ..., 4) are obtained experimentally by choosing the appropriate truncation parameter, which is defined as a ratio of the radius of the aperture to the beam waist. The IG^e(4, 4) mode is produced in the PQS Nd : YAG/Cr⁴⁺ : YAG microchip laser under decentred Gaussian beam pumping at a pump power of 2.6 W, the mode selection being achieved by reducing the truncation parameter. The threshold pump powers for different IG^e(n, n) modes are theoretically calculated to illustrate the mode selection process. The pulsed IG^e(n, n) (n ≥ 1) mode generation with a peak power exceeding 1 kW and a nanosecond pulse width is obtained in the PQS microchip laser, which is a potential laser source for forming flexible vortex arrays for optical tweezers.