Lecture 12: Revision Flashcards
(24 cards)
star
point source at infinity
plane-parallel waves brought to focus to
form image of star
aperture does not cover entire wavefront radiated by star - leads to
diffraction at apperture
angular resolution
a=1.22 lambda/D
actual image is
the convolution of the ideal image predicted by geometrical optics with the PSF
strehl ratio
I_psf(0) / I_airy(0)
planar wavefronts from the distant source are distorted by
turbulent layers of the atmosphere
phase variation across wavefront described by
phase structure function D(r)
by applying Kolomogorv model, one can derive the
dependence of the structure function on atmospheric parameters, specifically structure parameter Cn^2
Cn^2 characterises
the strength of fluctuations in refractive index
knowing phase structure function, can derive
the optical transfer function of the atmosphere
taking inverse FT of OTF
point spread func due to atmos
fried parameter
indication of the strength of phase fluctuations
integrate CN^2 wrt height
atmospheric seeing
angular size of PSF due to atmos
B=0.98 lambda /ro
guide stars
reference source of light within the isoplanatic patch
theta0=r0/h
sodium beacon
laser light used to excite sodium atoms in the upper atmos
strehl ratio used to quantify
the performance of an adaptive optics system
in corrected images,, what can be used
marechal approx
s approx e^-<E^2>
marechal approx allows one to
predict strehl ratio from known errors in wavefront sensing scheme
total residual phase variance is equal to
the sum of phase variances from all sources
etendue equ
G approx A omega
etendue remains
unchanged as light is transformed by lenses, mirrors, apertures etc
width of entrance slit
delta xi
= dx/dlambda dleta lambda_bp
linear disp x bandpass
