Generation of high-order Hermite–Gaussian modes in a flashlamp-pumped neodymium phosphate glass laser and their conversion to Laguerre–Gaussian modes

The Hermite–Gaussian modes up to the third order inclusive are generated in a flashlamp-pumped neodymium phosphate laser and converted to the corresponding Laguerre–Gaussian modes in an astigmatic $\pi/2$ converter. It is also shown that, by using a laser with the gain minimum on the axis of a plane-spherical resonator and changing its Fresnel number, it is possible to excite efficiently Laguerre–Gaussian modes with the field amplitude dependence $\sim{\sin\atop\cos}(l\varphi)$.