Efficiency is the Key
Ron Grubman, Blue Sky Research Inc.
Laser diodes are now widely used in industrial, computer, communications and consumer products. These tiny semiconductor lasers have all but replaced the HeNe laser in many applications in the visible range and enticed enough customers to produce a $2 billion world market last year.
Their compact size, economy, and ease of use make laser diodes an attractive laser light source, but their implementation is far from simple. In almost every application, conventional optics collect, collimate and focus the laser diode beam. In an ideal laser diode, the beam would be circular, with a low numerical aperture (NA), and have a diffraction-limited (spherical) wavefront, which would allow conventional optics to effectively produce the final beam desired for each application. Unfortunately, the reality of laser diodes is far from this ideal.
The main problem of most laser diodes is the strong asymmetric divergence of their emitted radiation. Diodes may also exhibit astigmatism, either naturally or because of the optical system that is used to correct the beam's ellipticity. The key to improving the diode beam shape and quality is to accomplish it as efficiently as possible, with as small an optical system as possible.