So I've tried the following:
k=zeros(length(xf),length(yf));
for i=1:length(xf)
k(xf(:,i),yf(:,i))=fwhm(:,i);
end
surf(xf,yf,k);
But now get
Subscripted assignment dimension mismatch.
Error in Merlion>pushbutton11_Callback (line 1920)
k(xf(:,i),yf(:,i))=fwhm(:,i);