A method of controlling beam quality and stability of a laser apparatus, the laser apparatus comprising, a diode laser (10) providing first radiation of at least a first wavelength, and a frequency conversion unit (12) configured to frequency-convert the first radiation from the diode laser and to output the frequency-converted radiation (213), the frequency-converted radiation having at least a second wavelength different from the first wavelength, the diode laser (10) comprising at least a first and a second section (222,223), a first contact (220) for injecting a first current (I.sub.1) into the first section (222), a second contact (221) for injecting a second current (I.sub.2) into the second section (223), and means for controlling a temperature of the diode laser; wherein the method comprises monitoring a first parameter indicative of the power content of a dominant lobe of the first radiation; iteratively determining a combination of respective values of the first current, the second current and the temperature at which combination of respective values the monitored first parameter and a stability parameter indicative of a fluctuation over time of the monitored first parameter each fulfills a respective predetermined optimization criterion; and setting the first current, the second current, and the temperature to the determined combination of respective values.

According to one embodiment, an optical element includes a first member. The first member includes a first region along a first plane. The first region includes a plurality of first structures. The plurality of first structures are arranged along a first direction at a first pitch and along a second direction at a second pitch. The first direction is along the first plane. The second direction is along the first plane and crosses the first direction. The first pitch is longer than the second pitch. A first length of the first region along the first direction is longer than a second length of the first region along the second direction.