WaveOpt_23 - Department of Electrical and Computer...

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Department of Electrical and Computer Engineering ECSE 527 Optical Engineering age evaluation Image evaluation References: Hecht 11.3.5 Smith ‘Introduction to Modern Optical Engineering’ Chapter 11 Andrew Kirk 2010 Diffraction 62
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Image evaluation •O p t i c a l systems do not form perfect images •T h e r e are two classes of degradation: –Geome t r i c aberrations from ray tracing iff ti bl – Diffraction blur hich of these will dominate ? Which of these will dominate ? What will be their impact on system performance? ©AGK 2010 Diffraction 63
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Learning outcomes After taking this section you will be able to: State the criteria that are used to determine whether an optical system is aberration limited or diffraction limited • Explain the significance of optical path difference •D e f i n e the Strehl ratio and use it to evaluate the performance of a system •U s e geometric spot size to evaluate performance s e ray intercept curves to estimate spot size and defocus e f i n e point and line spread functions etermine the modulation transfer function of a system and apply it Determine the modulation transfer function of a system and apply it to evaluate performance ©AGK 2010 Diffraction 64
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Outline •H o w far off are we ? – Optical path difference • Are we diffraction limited ? hl ti – Strehl ratio •W h a t does our spot look like ? oint and line spread functions Point and line spread functions •C a n we see clearly ? – Modulation transfer functions ©AGK 2010 Diffraction 65
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Criteria •O p t i c a l path difference (OPD): Wavefront departure from eal ideal • Strehl ratio: Deviation from Airy disk •P o i n t spread function (PSF): Spot profile •L i n e spread function (LSF): Line profile •R a d i a l energy distribution: Power within specific radius • Modulation transfer function (MTF): Spatial frequency response ©AGK 2010 Diffraction 66
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Optical path difference (OPD) OPD (waves) Optical system ith SA OPD y S P bject Paraxial with SA Object focus •E . g . for spherical aberration off axis rays are focused too close •W a v e f r o n t is curled inwards from ideal reference sphere Ideal wavefront Aberrated wavefront ©AGK 2010 Diffraction 67 p • Measure departure from spherical surface as OPD
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RMS and peak valley (PV) OPD •F o r a well corrected system, OPD /4 •T h i s is the Rayleigh limit (RL) o r irregular wavefronts, RMS OPD is used PV-OPD RMS-OPD RMS OPD PV-OPD / 4 i.e. /4 PV-OPD is equivalent to /16 RMS-OPD ©AGK 2010 Diffraction 68
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WaveOpt_23 - Department of Electrical and Computer...

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