Raúl de la Fuente

Spatial solitons pairing by cross phase modulation

Abstract We show that two beams of different color can simultaneously propagate undistorted as solitary waves in a homogeneous Kerr medium of both focusing or defocusing type thanks to cross phase modulation. These beams are obtained by pairing bright or/ and dark spatial solitons of identical width but different intensities.

The Offner imaging spectrometer in quadrature

This is a proposal and description of a new configuration for an Offner imaging spectrometer based on the theory of aberrations of off-plane classical-ruled spherical diffraction gratings. This new spectrometer comprises a concave mirror used in double reflection and a convex reflection grating operating in quadrature, in a concentric layout. A very simple procedure obtains designs that are anastigmatic for a given point on the entrance slit and a given wavelength. Specific examples show that the performance of this type of system improves the performance of analogous conventional in-plane systems, when compactness and/or high spectral resolution is of fundamental importance.

Amplitude and phase reconstruction by radial shearing interferometry.

We describe a new procedure for retrieving both amplitude and phase of an optical beam from radial shearing measurements. Information from the sheared interferogram is used to estimate and improve the beam and wavefront shape in successive iterations. We present computer simulations and experimental results that show the performance of the method.

Off-plane anastigmatic imaging in Offner spectrometers

In this paper, the imaging performance of an Offner concentric imaging spectrometer is analyzed when the spectrometer entrance slit is disposed arbitrarily on the plane that is parallel to the grating grooves and contains the common center of curvature. Astigmatism-corrected designs are obtained for off-plane incidence on the grating if one point on the slit is located on the Rowland circle of the primary mirror. In this case, the combined system of primary mirror plus diffraction grating provides two astigmatic line images oriented parallel and orthogonal to the plane of diffraction, with the former located on the same plane as the slit. Consequently, these images can be brought to a single focus on this plane by the tertiary mirror if its radius of curvature is chosen properly. In addition, coma aberration is simultaneously removed. These results can be applied to the design of two-mirror or three-mirror spectrometers, generalizing the concept of the best imaging circle and providing solutions to get anastigmatic imaging for two object points and two wavelengths.

Characterization of arbitrarily polarized ultrashort laser pulses by cross-phase modulation

We propose a technique for time resolution of the polarization state of ultrashort light pulses that also provides the overall time-varying phase of the pulse. This method is based on a spectral polarimetric analysis of the pulse after propagation through a Kerr medium. The feasibility of this method is demonstrated both numerically and experimentally.

Design of Dyson imaging spectrometers based on the Rowland circle concept

We aim to show that Dyson imaging spectrometers can be easily designed by applying the concept of the Rowland circle to refracting surfaces. This allows us to conceive an analytical procedure that is based on the removal of astigmatism at two wavelengths. Following this procedure, high-optical-quality spectrometers can be designed even for high speeds. Root-mean-square spot radii less than 2.5 μm are obtained for speeds as high as f/1.5, slit lengths of 15 mm, and wavelength ranges of 0.4-1.7 μm. Design examples are presented for classical Dyson spectrometers in which the detector is glued to the glass plane surface and for spectrometers with an air gap between this surface and the image plane.

White Light Spectral Interferometry as a Spectrometer Calibration Tool

For this paper, we used a white light interferometer in combination with spectral lamps to perform the wavelength calibration of a dispersive spectrometer. Illuminating the spectrometer with suitable spectral lamps gives the wavelength-pixel number relationship at discrete positions of the spectrometer detector array, and the wavelength-dependent phase difference at the output of the white light interferometer allows for a complete spectral calibration at any point on the detector (i.e., for every wavelength in the spectral range of the spectrometer). The details of this new calibration procedure are discussed, and two practical examples exhibiting the robustness of the method are presented. In addition, certain issues relating to minimizing the number of spectral lines used in the calibration procedure are examined.For this paper, we used a white light interferometer in combination with spectral lamps to perform the wavelength calibration of a dispersive spectrometer. Illuminating the spectrometer with suitable spectral lamps gives the wavelength-pixel number relationship at discrete positions of the spectrometer detector array, and the wavelength-dependent phase difference at the output of the white light interferometer allows for a complete spectral calibration at any point on the detector (i.e., for every wavelength in the spectral range of the spectrometer). The details of this new calibration procedure are discussed, and two practical examples exhibiting the robustness of the method are presented. In addition, certain issues relating to minimizing the number of spectral lines used in the calibration procedure are examined.

Two-wavelength anastigmatic Dyson imaging spectrometers

High-quality Dyson imaging spectrometers are designed by applying a telecentric condition for off-axis image points. By imposing this condition for two different wavelengths, designs presenting low aberrations for the whole spectral range of the system are obtained. A UV-TO-NIR fast design (f/1.5) exhibiting excellent optical performance is presented.

Imaging with classical spherical diffraction gratings: the quadrature configuration

We review the theory of spherical diffraction gratings with regard to their imaging properties in off-plane arrangements. Our study is restricted to gratings with equally spaced grooves, and it is focused on the quadrature configuration, where the incident and diffraction planes are orthogonal to each other. We identify regions of low astigmatism and propose some monochromator mounts.

Pupil aberrations in Offner spectrometers

The light path function (LPF) of an Offner spectrometer is presented. The evaluation of the LPF of this spectrometer enables its imaging properties to be studied for arbitrary object and image positions, while avoiding the more complicated analysis of intermediate images generated by the diffraction grating, which is often involved. A power series expansion of the LPF on the grating coordinates directly determines pupil aberrations of the generated spectrum and facilitates the search for configurations with small low-order aberrations. This analysis not only confirms the possibility of reducing low-order aberrations in Rowland-type mounts, namely astigmatism and coma, as predicted in previous studies, but also proves that all third-order terms in the series expansion of the aberration function can be canceled at the image of the design point and for the corresponding design wavelength, when the design point is located on a plane orthogonal to the optical axis. Furthermore, fourth-order terms are computed and shown to represent the most relevant contribution to image blurring. Third- and fourth-order aberrations are also evaluated for Rowland mounts with the design point located outside the aforementioned plane. The study described in this manuscript is not restricted to small angles of incidence, and, therefore, it goes beyond Seidel and Buchdahl aberrations.