Abstract

Experimental results are presented on the performance of an IR multidither adaptive-optics system with rotating, extended targets. A nine-zone deformable mirror with superimposed dithers was employed at 10.6 μm with spherical metallic targets of varying roughness and diameter. The results presented include open-loop discriminants, target speckle-noise spectra, and closed-loop beam quality obtained as functions of tarparameters. Experimental results are interpreted using a simplified model for the adaptive-get and system optics system and target.

© 1979 Optical Society of America

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References

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  1. J. E. Pearson, S. A. Kokorowski, M. E. Pedinoff, J. Opt. Soc. Am. 66, 1261 (1976).
    [Crossref]
  2. S. A. Kokorowski, M. E. Pedinoff, J. E. Pearson, J. Opt. Soc. Am. 67, 333 (1977).
    [Crossref]
  3. G. F. Gurski, N. T. Nomiyama, R. J. Radley, J. Wilson, J. Opt. Soc. Am. 67, 345 (1977).
    [Crossref]
  4. R. H. Freeman, R. J. Freiberg, H. R. Garcia, Opt. Lett. 2, 61 (1978).
    [Crossref] [PubMed]
  5. N. George, J. Opt. Soc. Am. 66, 1183 (1976).

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Figures (7)

Fig. 1
Fig. 1

Optical layout and control-loop block diagram. Input optics for deformable-mirror illumination are not shown. Deformable mirror is used as corrector and dither mirror.

Fig. 2
Fig. 2

Beam, target, and receiver sizes: (a) beam diameter at focus; (b) target sphere diameters (polished, 1.6-μm roughness, and 4.6-μm roughness); (c) receiver–aperture configurations (dimensions scaled down by factor of 10 from transmitter).

Fig. 3
Fig. 3

Open-loop control discriminants (V) vs OPD at 10.6 μm at center of deformable-mirror zone Φ (waves); discriminant voltage is rms of dither signal measured at output of preamp of Fig. 1 polished (solid line), 1.6-μm roughness (dashed line), and 4.6-μm roughness (dot-dash line) spherical targets.

Fig. 4
Fig. 4

Logarithmic power spectra for spherical targets rotating at 25 rpm with unobscured 1.1-cm receiver aperture for polished (solid line, modulation = 0.03), 1.6-μm roughness (dashed line, modulation = 0.22), and 4.6-μm roughness (dot–dash line, modulation = 0.23) targets.

Fig. 5
Fig. 5

Logarithmic power spectra for 4.6-μm roughness target at 25 rpm: 1.1-cm clear (solid line, modulation = 0.22), 1.1-cm annular (dash–double-dot line, modulation = 0.31), 2-cm annular (dashed line, modulation = 0.17), 2.0-cm clear (dot–dash line, modulation = 0.15).

Fig. 6
Fig. 6

Variation of time-averaged integrated irradiance profile with target rotation. (a) Ω = 5 rpm, Vdc = 2.26 V; (b) Ω = 25 rpm, Vdc = 0.84 V; (c) Ω = 50 rpm, Vdc = 1.15 V. 4.6-μm, 1.9-cm diam sphere with 1.1-cm annular receiver.

Fig. 7
Fig. 7

Integrated irradiance at D = 8 mm for 4.6-μm, 1.9-cm diam sphere: ○, 2-cm clear aperture; △, 1.1-cm clear aperture; ●, 1.1-cm annulus; ▲, 2.0-cm annulus.

Equations (11)

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σ 2 ( Φ ) = σ 0 2 ( 1 + Φ 2 ) ,
P ( R T ) = P 0 { 1 - exp [ - 2 R T 2 / σ 0 2 ( l + Φ 2 ) ] } P 0 [ 1 - exp ( - 2 R T 2 / σ 0 2 ) exp ( 2 R T 2 Φ 2 / σ 0 2 ) ] .
D ( Φ ) = 1 P ( R T ) P ( R T ) Φ [ 2 ( R T 2 σ 0 2 ) exp ( - 2 R T 2 / σ 0 2 ) 1 - exp ( - 2 R T 2 / σ 0 2 ) ] ( Φ ) .
S ( f ) = d x h R { [ x 2 + ( f λ Ω ) 2 ] 1 / 2 } h T { [ x 2 + ( f λ Ω ) 2 ] 1 / 2 } ,
S ( f ) = 4 π f H 1 ( 2 π D f R Ω ) ( 2 π D f R Ω ) ,
f m = 7 R Ω 2 π D R ( Hz ) , = 800 Hz for D R = 1.1 cm at 25 rpm , = 450 Hz for D R = 2.0 cm at 25 rpm .
S ( f ) = σ 2 f c exp ( - f / f c ) ,
Δ Φ rms 2 = π 2 f L B d ( σ η ) 2 exp ( f 1 / f c ) [ 1 - exp ( - B d / f c ) ] ,
f c = B d ln [ 1 + ( B d / f 1 ) ] ( Hz ) ,
Ω M = B d ( f c Ω ) ln [ 1 + ( B d / f 1 ) ( rpm ) .
Ω min = B d ( f c Ω ) ln [ 1 + ( B d / f 1 ) ] = 800 ( Hz ) 35 ( Hz / rpm ) ln 2 = 33 rpm for 1.1 - cm annular receiver ,

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