how to convrt the FWHM value to picoseconds when given in nanometers for optical gaussian pulses.

I am generating a optical gaussian pulse. I have got the FWHM values in nanometer. I want values in picoseconds.

Answer 1

[John BG]

Mr Egan has posted in Mathworks website the following function:

function width = fwhm(x,y)

% function width = fwhm(x,y)
%
% Full-Width at Half-Maximum (FWHM) of the waveform y(x)
% and its polarity.
% The FWHM result in 'width' will be in units of 'x'
%
%
% Rev 1.2, April 2006 (Patrick Egan)

y = y / max(y);
N = length(y);
lev50 = 0.5;
if y(1) < lev50                  % find index of center (max or min) of pulse
    [garbage,centerindex]=max(y);
    Pol = +1;
    disp('Pulse Polarity = Positive')
else
    [garbage,centerindex]=min(y);
    Pol = -1;
    disp('Pulse Polarity = Negative')
end
i = 2;
while sign(y(i)-lev50) == sign(y(i-1)-lev50)
    i = i+1;
end                                   %first crossing is between v(i-1) & v(i)
interp = (lev50-y(i-1)) / (y(i)-y(i-1));
tlead = x(i-1) + interp*(x(i)-x(i-1));
i = centerindex+1;                    %start search for next crossing at center
while ((sign(y(i)-lev50) == sign(y(i-1)-lev50)) & (i <= N-1))
    i = i+1;
end
if i ~= N
    Ptype = 1;  
    disp('Pulse is Impulse or Rectangular with 2 edges')
    interp = (lev50-y(i-1)) / (y(i)-y(i-1));
    ttrail = x(i-1) + interp*(x(i)-x(i-1));
    width = ttrail - tlead;
else
    Ptype = 2; 
    disp('Step-Like Pulse, no second edge')
    ttrail = NaN;
    width = NaN;
end

link: http://uk.mathworks.com/matlabcentral/fileexchange/10590-fwhm/content/fwhm.m

Wolfram has a table you may find useful

link: http://mathworld.wolfram.com/FullWidthatHalfMaximum.html%20 Hope it helps.

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thanks

John

[e-mail]

[Vijendra Kumar Prajapati]

Thanx

[Thor]

Could anyone help me to understand the code?