Design of a compact device to generate and test beams with orbital angular momentum in the EUV: erratum.

This erratum includes a relevant additional reference for the article Appl. Opt.56, 8048 (2017)APOPAI0003-693510.1364/AO.56.008048.

Design of a compact device to generate and test beams with orbital angular momentum in the EUV.

We present a compact design to generate and test optical-vortex beams with possible applications in the extreme ultraviolet (EUV) region of the electromagnetic spectrum. The device consists of a diffractive mask where both the beam with orbital angular momentum and the reference wavefront to test its phase are generated. In order to show that the proposal would work in the EUV, simulations and proof-of-principle experiments were performed, using typical parameters for EUV holography scaled to visible wavelengths. As the simplest case, we consider the well-known Laguerre-Gaussian (LG)-like beams, which have a single vortex in the propagation axis. To further test the versatility of the device, we consider Mathieu beams, more complex structured beams that may contain several vortices. In the experiment, a spatial light modulator was used to display the mask. As examples, we show the results for a LG-like beam with topological charge ℓ=1 and Mathieu beams with topological charge ℓ=2 and ellipticity q=2. These results show the potential of the device to generate a variety of beam shapes at EUV wavelengths.

General compressor for ultrashort pulses with nonlinear chirp.

A new type of grating compressor capable of compensating, in principle, for any arbitrary group-delay dispersion is described. The system relies on a specially designed grating with a variable groove spacing along its surface as well as a variable angle of incidence. In this manner each wavelength actually sees a different grating, always at Littrow incidence, that gives rise to distinct group delays. The design equations are derived, and the particular case of a cubic compressor is discussed. It is shown that, within practical limits, both quadratic and cubic terms can be simultaneously compensated for in typical optical fibers.

Fringe visibility in lateral displacement measurement from double-exposure laser photographs.

The measurement of lateral displacement employing a doubly exposed speckle photograph according to the methods proposed by Archbold et al. and by Butters and Leendertz has been studied. The fringe visibility has been found as a function of the displacement and the resolution of the observing system. The spatial extent of the source has also been considered when a spectral lamp is used in the observing step. The use of an incoherent source replacing the laser in the observing step proved to be of interest because it reduces the speckle in the observed fringes.