Jerold B. Lisson

Phase-conjugate Fizeau interferometer

We describe a phase-conjugate interferometer that consists of a partially transmitting conventional mirror placed in front of and in close proximity to a phase-conjugate mirror. The interferometer is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional (nonphase-conjugate) interferometers, and produces a direct representation of an incident wave front. We have constructed such a device using internally self-pumped phase conjugation in barium titanate and have used the device to characterize the wave front produced by an aberrated optical system.

Estimation of imaging performance using local optical quality factor metrics

Traditional methods of assessing optical quality are based primarily on global parameters such as the rms wavefront error or performance quantifiers such as the optical quality factor (OQF). Global parameters that characterize performance, such as rms, are indirectly correlated with imaging quality because they do not account for the spatial distribution of the errors in the aperture. Although the conventional OQF is related to performance for systems affected with arbitrary aberration forms, it does not supply information that is useful for correcting the local regions of an optical component (e.g., mirror surface). A system is presented that is directly correlated with imaging quality. The system, denoted localized wavefront performance analysis (LWPA), evaluates quality on the basis of a subpupil or local OQF (LOQF) that is specific to discrete regions of the aperture. This information is used to produce a performance map, LOQF versus pupil position, to pinpoint for correction those wavefront error regions with the lowest values. LWPA theory is described heuristically and a supporting test case is presented.

Use of localized performance-based functions for the specification and correction of hybrid imaging systems

Localized wavefront performance analysis (LWPA) is a system that allows the full utilization of the system optical transfer function (OTF) for the specification and acceptance of hybrid imaging systems. We show that LWPA dictates the correction of wavefront errors with the greatest impact on critical imaging spatial frequencies. This is accomplished by the generation of an imaging performance map-analogous to a map of the optic pupil error-using a local OTF. The resulting performance map a function of transfer function spatial frequency is directly relatable to the primary viewing condition of the end-user. In addition to optimizing quality for the viewer it will be seen that the system has the potential for an improved matching of the optical and electronic bandpass of the imager and for the development of more realistic acceptance specifications. 1. LOCAL WAVEFRONT PERFORMANCE ANALYSIS The LWPA system generates a local optical quality factor (LOQF) in the form of a map analogous to that used for the presentation and evaluation of wavefront errors. In conjunction with the local phase transfer function (LPTF) it can be used for maximally efficient specification and correction of imaging system pupil errors. The LOQF and LPTF are respectively equivalent to the global modulation transfer function (MTF) and phase transfer function (PTF) parts of the OTF. The LPTF is related to difference of the average of the errors in separated regions of the pupil. Figure

Phase-conjugate pointing error sensing

Nonlinear optical phase conjugation, obtained by four-wave degenerate mixing is utilized to create a new form of optical pointing error sensor-theActiveOptical Self-Referencing Component(AO-SRC). Thisdevicewas conceived and constructed during a 1988 nonlinearoptic initiative thatwas designed to demonstrate the expanded degrees of freedom available for designs that incorporate nonlinear optic elements. The AO-SRC concept was successfully demonstrated and verified that an absolute, seff-referenced form of pointing sensor couldbeachievedwith the use of nonlinear photorefractive design elements. The self-referencing capabiity is obtained from the ideal and generalized phase-conjugate reflectance from nonlinear mirrors. The absolute capability is related to the optical relationship between the phase-conjugate and the Fresnel (specular) reflected energy from a common nonlinear medium. It is seen that the same physical mechanism responsible for the well known self-referencing capability of phase-conjugate interferometers (-i.e. elimination ofthe reference mirror) can be used to constructa high sensitivity, self-referencing, pointing error sensor. Current nonlinear materials such as barium titanate are limited to maximum input apertures ofabout 12 millimeters diameter. Since sensitivity (minimum resolvable angle) is inversely related to aperture alze, the maximum size of nonlinear media may represent a severe limiting factor for some AO-SRC device forms. Two mechanisms associated with nonlinear optic materials were used to ease this constraint, specifically: 1. Electric Field Enhancement: Application of an electric field seross the mdium was used to construct a phase-shifting, phase-conjugate interferometer. This construction will yield an increase in sensitivity of 1-2 orders of magnitude. 2. Nonlinear Synthetic Aperture: Utilization of the self-coupling capability of discrete nonlinear materials was shown to yield effective aperture sizes of arbitrary dimension. It is shown that the AO-SRC concept can be applied to such critical tasks as the assessment of the optical coherence achieved in phasing (pointing error and piston) segmented or synthetic aperture optical systems.