Abstract

High-quality collimation and focusing of laser diode beams is hindered by their asymmetric divergence and elliptical beam section. These result from the large aspect ratio of the source. In gain-guided diode lasers the beam also suffers astigmatism due to the lensing effects of the nonuniform current porofile. A holographic correcting and collimating element for such diodes is desirable for its low mass-production cost and small dimensions. Efficient holograms cannot, however, be recorded directly with the infrared wavelengths of diode lasers, and normally large aberrations and low efficiencies are obtained when recording with shorter wavelengths. Using a recursive holographic method1 we recorded a hologram with blue light that collimates a 820 nm diode beam with low aberrations and high efficiency. This element corrects for the diode's astigmatism and ellipticity and achieves near-diffraction-limited collimation. The design can also alleviate effects due to diode wavelength instability.

© 1992 Optical Society of America