Does FresnelWavefront.apply_lens_power have inaccessible if branches?

[Jordan-Dennis]

Hi all,
My question pertains to the following snippet of code from FresnelWavefront.apply_lens_power.

if not self.spherical
    if np.abs(self.z_w0 - self.z) < self.z_r:
        _log.debug('Near-field, Plane-to-Plane Propagation.')
        z_eff = 1 * optic.fl

    else:
        # find the radius of curvature of the lens output beam
        # curvatures are multiplicative exponentials
        # e^(1/z) = e^(1/x)*e^(1/y) = e^(1/x+1/y) -> 1/z = 1/x + 1/y
        # z = 1/(1/x+1/y) = xy/x+y
        z_eff = 1.0 / (1.0 / optic.fl + 1.0 / (self.z - self.z_w0))
        _log.debug('Inside Rayleigh distance to Outside Rayleigh distance.')
        self.spherical = True

else:  # spherical input wavefront
    if np.abs(self.z_w0 - self.z) > self.z_r:
        _log.debug('Spherical to Spherical wavefront propagation.')
        _log.debug("1/fl={0:0.4e}".format(1.0 / optic.fl))
        _log.debug("1.0/(R_input_beam)={0:0.4e}".format(1.0 / r_input_beam))
        _log.debug("1.0/(self.z-self.z_w0)={0:0.4e}".format(1.0 / (self.z - lf.z_w0)))

        if (self.z - self.z_w0) == 0:
            z_eff = 1.0 / (1.0 / optic.fl + 1.0 / (self.z - self.z_w0))
        else:
            z_eff = 1.0 / (1.0 / optic.fl + 1.0 / (self.z - self.z_w0) - 1.0 / r_input_beam)

    else:
        _log.debug('Spherical to Planar.')
        z_eff = 1.0 / (1.0 / optic.fl - 1.0 / r_input_beam)
        self.spherical = False

Specifically, I believe that the if (self.z - self.z_w0) == 0: in the else branch of the outer if statement is not reachable. If I have interpreted it correctly, (self.z - self.z_w0) == 0 implies that the wavefront is at the waist, where it is planar. Under this assumption the else branch of the outer if statement should not have been accessed. Furthermore, at the next level of nesting np.abs(self.z_w0 - self.z) > self.z_r is checked and since the Rayleigh distance, z_r, is a definitely positive quantity it should not be possible to satisfy both: np.abs(self.z_w0 - self.z) > self.z_r and (self.z - self.z_w0) == 0.

As a second note the (self.z - self.z_w0) == 0 is used in division, implying it is a known amount and z_eff is 0 (1 / inf). If you don't mind me asking is there an original reference for this code, I have scrolled back through Lawrence et. al. but have been unable to find any references to z_eff (I do vaguely remember it been there). If you could point me in that direction it would be greatly appreciated.

[Jordan-Dennis]

Hello again,
Upon further review I believe that I may have spotted a second inconsistency in if the wavefront is considered spherical. The line np.abs(self.z - self.z_w0) < (or >) self.z_r seems to be used to determine if the wavefront is spherical or planar at many if statement branches. However, the top if statement of the same function uses np.abs(self.z_w0 - self.z) > self.rayleigh_factor * self.z_r considering also the rayleigh_factor (2. by default). I do not perceive the reason for this difference.

Thanks again

Jordan