venerdì, febbraio 22, 2008

Yet another slow motion movie of speckles

This is anoher movie. The "taylor screen" in this case has been produced by inverse fourier transform and should be of better quality (in the sense it is closer to the statistical properties the wavefront should have, as described by Fried, Statistics of a geometric representation of wavefront distortion, JOSA 55-11, 1965).

The time step corresponds to the motion of the taylor screen of 1% of the diameter (~1ms in typical conditions).

See also (in the comments there is the code fragment that produces the movie)


  • ------ R source code (GDD package needed)

    turb.ft <- function (size, friedratio=1, pad=2) {
    n <- nextn (size*pad)
    b <- matrix (rnorm (n^2)+1i*rnorm(n^2), n, n)
    rho <- make.rho.fdom (n)
    b <- b * sqrt (0.023*rho^(-11/3)/friedratio^(5/3))
    b[rho == 0] <- 0
    resize (Re (ift (b)), size, size)/ (2*pi)

    size <- 101
    t <- turb.ft(size*11,size*11)
    t <- t/sd(as.vector (t))
    p <- pupil(size)
    step <- 1
    nsteps <- floor((size*10)/step)
    star <- star.test(p,0,size=40,pad=4,draw=FALSE)
    zmax <- max(star)
    gamma <- 2.2

    GDD("turbulence", type="gif", width=400, height=400)

    for (i in 1:nsteps) {
    tt <- t[((i-1)*step+1):((i-1)*step+size),(size*1):(size*2)]
    rms <- sd(as.vector (tt))*4
    star <- star.test(p,0,size=40,pad=4,draw=FALSE)
    image ((star/zmax)^(1/gamma), zlim=c(0,1), col=gray256, asp=1, bty='n', axes=FALSE)

    By Blogger Mauro Da Lio, at 23 febbraio 2008 13:28  

Posta un commento

<< Home