Active mirror assembly

• US 5,159,498 A
• Filed: 03/01/1990
• Issued: 10/27/1992
• Est. Priority Date: 03/01/1990
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Hubbard, James E. Jr.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Neuyen, Thong
• Application Number:
  US07/486,955
• Time in Patent Office: 971 Days
• Field of Search: 350/607, 350/487, 350/358, 350/360, 350/3.82, 350/3.83, 350/572, 350/167, 359/1, 359/10, 359/11, 359/15, 359/32, 359/34, 359/245, 359/247, 359/254-271, 359/290-300, 359/846-849, 359/900, 356/353-390
• US Class Current: 359/847
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A mirror and system for wavefront control includes a piezoelectrically active pellicle with a conductive front mirror surface, and an electron gun for depositing charge on the rear surface of the pellicle. The pellicle is formed of facing plies of polyvinylidene fluoride having opposite poling, so that efficient bimorph actuation is achieved while maintaining substantially constant pellicle thickness and stable x-y planar position coordinates. A phase corrector plate provides a fixed flatness correction for irregularities of the mirror surface, and an initial charge distribution is applied to achieve a reference mirror contour. Potentials above and below a front surface reference potential, and different frame rates, are achieved by controlling the electron energy to selectively charge by primary or secondary charging processes. A feedback system may establish the initial reference contour, and thereafter effect real time wavefront adjustment of a beam reflected from the front mirror surface.

Claims

1. An active mirror assembly for forming a spatially-varying surface contour to reflect and change a wavefront of light directed thereat, such assembly comprising:

a piezoelectrically active membrane formed of a deformable material and having first and second sides with an electrically conducting and reflective mirror surface formed on said first side;

means for maintaining said first side at a reference potential;

mounting means for securing said membrane in a fixed mounting plane, the reflective mirror surface being characterized by a surface irregularity such that light reflected from the mirror surface undergoes an irregular phase delay distribution when the membrane is in a relaxed or zero potential state;

a phase correction plate in front of said mirror surface, said phase correction plate being holographically formed for introducing into light directed at the mirror surface a two-dimensional phase delay distribution complementary to the irregular phase delay distribution due to the surface irregularity of said reflective mirror surface; and

means for projecting charge at said second side to develop a two dimensional varying charge distribution effective to piezoelectrically deform said membrane in relation to the fixed mounting plane.

2. An active mirror assembly according to claim 1, wherein said piezoelectrically active membrane is formed of plural lamina of piezoelectric material, adjacent lamina having opposite poling.

3. An active mirror assembly according to claim 2, wherein said piezoelectric material is a polyvinylidene fluoride (PVDF).

4. An active mirror assembly according to claim 1, wherein said reflective mirror surface is a grounded conductive coating under one micron thick.

5. An active mirror assembly according to claim 1, wherein said means for projecting charge includes means for varying the energy of electrons striking said second side to develop a charge distribution above and below said reference potential.

6. A light reflecting mirror assembly comprising a bimorph pellicle consisting of:

first and second piezoelectrically active film layers of opposing polarity joined together along a common surface, each layer thereby having one outer surface, an electrically conductive reflective mirror coating on the outer surface of one said layer; and

means for introducing a two-dimensional phase delay distribution complementary to a phase distribution produced in light by reflection from an irregular surface of the reflective coating on the outer surface.

7. A method of altering a light wavefront comprising the steps of:

directing the light wavefront at a front surface of a piezoelectrically active membrane having a reflective and electrically conductive mirror coating formed on said front surface which is effective to maintain said surface at a reference potential;

further directing the light wavefront at a phase corrector plate to introduce a phase delay in the light wavefront complementary to phase changes introduced by reflection at said mirror coating from surface irregularities of the conductive mirror coating when said membrane is in a relaxed or zero-potential state; and

directing an electron beam at a rear surface of said membrane to develop a varying charge distribution on said membrane, whereby the front surface assumes a defined contour for altering the phase distribution of the light wavefront directed at said front surface.

8. The method of claim 7, further comprising the steps of;

directing the altered wavefront to a photodetector to develop a time-varying signal representative thereof; and

controlling the electron beam in accordance with said time varying signal.