Holographic diffractive collimators based on recording with homocentric diverging beams for diode lasers

Abstract

A single collimating transmission off-axis blazed surface-relief holographic diffractive element that corrects the ellipticity and the astigmatism of a diode-laser beam was designed. The procedure was applied to a hypothetical laser operating at a wavelength of 633 nm that possesses extremely large astigmatism and relatively small ellipticity together with small diverging angles of the laser beam. The element was recorded with only homocentric diverging beams that had pure spherical wave fronts. Because of the off-axis nature of the element, the aberration of asymmetry had to be corrected. The element was tested in a reciprocal way when the incident wave was a collimated He-Ne laser beam. A diffraction-limited beam was obtained that was as large as approximately half of the designed aperture.

<title>Holographic transformation between optical beams with spherical and cylindrical wave fronts</title>

“…In this case bundles of rays are supposed to be narrow and also angles among axes of bundles are small. A general holographic equation is given by the relation among phases (1) where is the phase of the wave front of the outgoing beam, is the phase of the wave front of the incoming beam and 2 and are the phases of recording beams. If the bundles arc not narrow aberrations of higher orders must be taken into account.…”

“…One element collimates the beam in one plane and the other element collimates the beam in the plane perpendicular to the first plane. Four equations for calculation of the recording parameters are sin0=0+p(sinc2-sincEj) (30) 1 (1 1\ (31) .9 As the collimation is in one plane only the transformation between spherical and cylindrical wave fronts takes place.…”

“…Single-element holographic systems for collimation of infrared beams with lower ellipticity were described in [1]. Particularly holographically recorded elements can be obtained very easily.…”