real function convolution(dcav)
      real siglaser
      real sigcav,dcav

      sigcav = 1000.0*dcav/2./sqrt(2.*log(2.0))

      siglaser=130920/2./sqrt(2.*log(2.0))

c      siglaser=56000/2

      convolution = sigcav/sqrt(sigcav**2+siglaser**2)

      return
      end