Techniques for Matching Laser TEM(00) Mode to Obscured Circular Aperture.

The performance of an optical telescope system with a centrally obscured aperture illuminated by a laser operated in the TEM(00) mode is analyzed in terms of antenna gain. This permits calculation of power budgets for optical radar and communication systems by substitution into the microwave range equations in common use. Practical techniques for increasing the antenna gain using conical axicons and aspheric lenses are presented. For example, if 0.25 of the aperture area is obscured, increases in the antenna gain of two times have been obtained using a conical axicon. The analysis also indicates that this approaches the maximum theoretical gain obtainable from an obscured aperture. The optimum method of interfacing the laser output with the obscured optical system and experimental results are also presented.