Didia P. Salas-Peimbert

Measuring the effective focal length and the wavefront aberrations of a lens system

A new, simple method to measure the effective focal length of a thick lens or lens system in the laboratory when a lens nodal bench is not readily available is described. Use is made of the Talbot autoimaging effect by placing the lens in a collimated light beam, with a Ronchi ruling in front of the lens and another in the refracted beam.

Ophthalmic lenses measurement using Hartmann test

This paper describes a simple Hartmann test data interpretation that can be used to evaluate the performance in spherical ophthalmic lenses. Considering each spot of the Hartmann pattern like a single ray, using traditional ray tracing analysis it is possible to calculate the value of the spherical power in the point corresponding with each spot. The values of spherical power for each spot obtained by this procedure are used to obtain a spherical power distribution map of the entire lens.

Simulation of simple capacitive-isolated LED drivers

Given that the use of electrolytic capacitors and inductors reduces the lifetime and efficiency of LED based lamps, this work proposes an LED driver where only ceramic capacitors are used, it also replaces the use of inductors by an array of capacitors and switches. The proposed configuration is compared to a classical Buck topology. A study of the input signal behavior is performed as a function of the frequency of the control signals of the switches.

Generation of a spiral wave using amplitude masks

Optical beams of Bessel-type whose transverse intensity profile remains unchanged under free-space propagation are called nondiffracting beams. Experimentally, Durnin used an annular slit on the focal plane of a convergent lens to generate a Bessel beam. However, this configuration is only one of many that can be used to generate nondiffracting beams. The method can be modified in order to generate a required phase distribution in the beam. In this work, we propose a simple and effective method to generate spiral beams whose intensity remains invariant during propagation using amplitude masks. Laser beams with spiral phase, i.e., vortex beams have attracted great interest because of their possible use in different applications for areas ranging from laser technologies, medicine, and microbiology to the production of light tweezers and optical traps. We present a study of spiral structures generated by the interference between two incomplete annular beams.

Generation of a spiral wave by modified annular slit

Optical beams of Bessel-type, whose transverse intensity profile remains unchanged under free-space propagation, are called nondiffracting beams. In this paper, we propose a simple and effective method to generate spiral beams whose intensity remains invariant during propagation using amplitude masks. We show how the interaction between two incomplete annular beams leads to the formation of a spiral structure. Experimental observations are presented to show the characteristic features of the spiral structure generated. We can modulate the nondiffracting beam modifying the amplitude mask.

Method of analysis to measure the tangential curvature in a test sphere

Several techniques have been used to determine the radius of curvature of the cornea. In this article, we describe the use of a method obtained trough ray analysis, based in geometrical analysis and lateral magnification equation. A pattern of an increasing point was displayed in a flat screen monitor; images of this point were captured for a test sphere with a CCD camera. The obtained data was then processed for the calculation of the sphere curvature. The experimental setup is presented.

Method of analysis to measure the spherical power in ophthalmic lenses

In this paper we propose a new method of analysis to obtain the spherical power in ophthalmic lenses based on ray traces of geometric optics techniques, formation, capture and image processing. We determine the spherical power in ophthalmic lenses considering the total magnification of the optical system and the Gausss formula. A simple, practical and easy to implement experimental setup is presented for the measurement of positives and negative lenses. The setup consists in a circular object displayed in a LCD monitor, the ophthalmic lens to be measured and a digital camera in order to send information to a PC containing the software algorithm which calculates and displays the spherical power.

A Proposal for Wavefront Retrieval from Hartmann Test Data

In the classical Hartmann test analysis, the transverse aberrations are represented by small straight segments joining two consecutive measured points in the pupil. In the analysis presented in this paper we propose the wavefront to be synthesized by many nonflat functions whose domains are the squares defined by the square unit cell defined by an array of holes in the Hartmann screen placed at the exit pupil of the system. Two advantages of this method are that a higher precision in the wavefront retrieval is obtained and second that the local curvatures and astigmatism with their corresponding axes are obtained.

Computer-based null test compensation for ophthalmic lenses

In this paper, we will describe a method used to obtain the power error distribution map for a spherical well corrected ophthalmic lens. The proposed method uses a computer to perform a null test compensation to probe the real refractive correction state of the lens under test. The Hartman test is used to probe an ophthalmic lens and subtract the ideal power distribution map corresponding to the same lens design. In this way we obtain the power error distribution map of the lens. The proposed method may be useful in mass production of spherical ophthalmic lenses.