R. de la Fuente

Analytical design of an Offner imaging spectrometer

We present the analytical design of an imaging spectrometer based on the three-concentric-mirror (Offner) configuration. The approach presented allows for the rapid design of this class of system. Likewise, high-optical-quality spectrometers are obtained without the use of aberration-corrected gratings, even for high speeds. Our approach is based on the calculation of both the meridional and the sagittal images of an off-axis object point. Thus, the meridional and sagittal curves are obtained in the whole spectral range. Making these curves tangent to each other for a given wavelength results in a significant decrease in astigmatism, which is the dominant residual aberration.RMS spot radii less than 5 mm are obtained for speeds as high as f/2.5 and a wavelength range of 0.4-1.0 microm. A design example is presented using a free interactive optical design tool.

Fourier analysis of non-paraxial self-focusing

In this paper we deduce a vectorial non-paraxial equation describing the self-focusing of light in a homogeneous isotropic Kerr medium. The equation is derived via transformation to the spatial frequency domain, which clarifies the physical nature of the approximations made. We also present numerical solutions for a linearly polarized Gaussian input beam and discuss the dependence of the self-focusing length on beam width and input power.

Unusual modulation instability in fibers with normal and anomalous dispersions

Abstract The propagation of an amplitude modulated signal in a nonlinear dispersive single mode fiber is considered in the unusual case where the amplitude of side-bands is highly above the amplitude of the carrier. We show that an instability can occur and that amplification of the carrier can take place as well with normal than with anomalous dispersion, and for given values of intensity and modulation frequency.

Wavefront sensing by diffracted beam interferometry

We consider the reconstruction of an optical wavefront by means of the interference of a light beam with a diffracted copy of itself. We present the basis of the method and a numerical algorithm for phase retrieval from the experimental data.

A windowing/pushbroom hyperspectral imager

We show that any pushbroom hyperspectral imager can be converted into a windowing one by only attaching in front of it a simple dispersive element. The resulting device displays the same spectral resolution than the former one. To test this idea we have built a pushbroom imaging spectrograph in our laboratory. A plane transmission grating has been used as the dispersive element. We point out the main characteristics of these devices and we show some illustrative results.

A perturbative study of spatial soliton-induced phase volume gratings

A perturbative theory has been used to investigate the nonlinearly laser-induced grating formed by the superposition of two elliptical beams inside a Kerr medium. The effect on both soliton propagation and induced guiding of a weak beam has been studied.

Simultaneous Characterization of Surface and Buried Waveguides Produced by Ion-exchange in Glass

Abstract A simultaneous modelling of surface and buried waveguides is presented. It is based on an approximate solution of the nonlinear diffusion equation solved under different boundary and initial conditions. Experimental results of buried waveguides produced by potassium-sodium exchange in soda-lime glass are presented.

Optical Configurations for Imaging Spectrometers

Imaging spectrometers or hyperspectral imagers are radiation sensors that provide a continuous collection of spectral images of an inhomogeneous scene, allowing to obtain a spectral signature of each point in the scene. They are applied to perform many different tasks such as accurate mapping of wide areas, object identification and recognition, target detection, process monitoring and control, clinical diagnosis imaging and environment assessment and management. Application areas include forestry, geology, agriculture, medicine, security, manufacturing, colorimetry, oceanography, ecology and others [1].

Measurement of the polarization dynamics of ultrashort pulses by using nonlinear phase modulation and channelled spectroscopic polarimetry

Recently we presented a vectorial pulse characterization method based on the spectral polarimetric analysis of femtosecond laser pulses before and after propagation through a Kerr medium. In this work we present an improvement of the method. We propose to carry out the spectral polarimetric analysis by using the technique named spectroscopic polarimetry with a channelled spectrum which has been developed by Oka and Kato (1999 Opt. Lett. 24 1475). This combination supposes an important improvement of the data acquisition process both in velocity and accuracy.

Amplitude and phase characterization by diffracted beam interferometry: blind dbi

Diffracted beam interferometry is a self referenced method characterization technique whose operation principle is based on the reconstruction of the phase of a beam starting from the interference data between the beam and its diffracted copy. The phase is recovered indirectly by means of an iterative algorithm that relates the irradiances of the interfering beams and its phase difference. The first experimental demonstration of DBI was implemented on a Mach-Zenhder interferometer which incorporated an afocal imaging system in each arm, in order to form an image of a common object in different planes at the output of the interferometer. The irradiance data as well as the phase difference data were picked up from one of the image planes and they were introduced in the iterative algorithm. In this work we discuss a modification of the algorithm that allows to reconstruct simultaneously the amplitude and phase of the wavefront starting from, exclusively, the phase difference between the two waves that interfere in one of the image planes. This new algorithm improves the reconstruction process because the data acquisition process is faster and consequently the method is less influenced by environment disturbances. The method has been applied successfully to the characterization of phase plates and laser beams as well as to the local characterization of ophthalmic lenses.