Ivo Koudela

Recording of holographic diffraction gratings in photopolymers: Theoretical modelling and real-time monitoring of grating growth

Abstract Recording of holographic volume diffraction gratings in Du Ponts photopolymer HRS-150 is studied theoretically and experimentally. Particular attention is paid to the dynamics of the recording process. The temporal evolution of holographic gratings is monitored for a range of illumination intensities in two ways: (i) by means of a multiple-exposure approach when intensity profiles of recording beams are uniform, many holographic exposures are necessary and each exposure is carried out for a particular value of the total illumination intensity; (ii) by means of a single-exposure approach when intensity profiles of recording beams are strongly Gaussian and a volume grating with spatially distributed diffraction efficiency arises, depending on a local (average) value of the total illumination intensity. The second approach proves to be a useful tool providing us very quickly with qualitative information about the dynamics of the recording process while the first one, which is much more time-consumi...

Holographic diffractive collimators based on recording with homocentric diverging beams for diode lasers

A single collimating transmission off-axis blazed surface-relief holographic diffractive element that corrects the ellipticity and the astigmatism of a diode-laser beam was designed. The procedure was applied to a hypothetical laser operating at a wavelength of 633 nm that possesses extremely large astigmatism and relatively small ellipticity together with small diverging angles of the laser beam. The element was recorded with only homocentric diverging beams that had pure spherical wave fronts. Because of the off-axis nature of the element, the aberration of asymmetry had to be corrected. The element was tested in a reciprocal way when the incident wave was a collimated He-Ne laser beam. A diffraction-limited beam was obtained that was as large as approximately half of the designed aperture.

Near-field characteristics of periodic surface relief diffraction structures from far-field measurements

Abstract Near-field characteristics of periodic surface structures, i.e. their surface relief, may be determined by measuring the diffraction efficiency, i.e. from far-field measurements, if the relief is described by a known periodic function with a few unknown geometric parameters. This method is formulated for one- and two-dimensional periodic structures and demonstrated for some holographic grating structures.

Holographic optical element converting the Gaussian laser beam into a more uniform one

A surface relief holographic grating is designed for the transformation of a Gaussian laser beam into a beam with a flattened plateau in its central part. The depth of grating grooves varies over the surface in order to achieve a distribution of diffraction efficiency complementary to the intensity profile of the laser beam to be transformed. The appropriate efficiency distribution over the grating can be obtained by a technological process during the exposure and development. Experiments have proved that produced grating samples can sufficiently flatten the Gaussian beam, and that the degree of the beam flattening can be easily controlled.

Holographic transmission surface-relief grating couplers for backplane interconnections

Holographic surface-relief diffractive elements with an inclined profile working as transmission grating couplers for backplane interconnects were fabricated and their diffraction efficiency was measured during a step-by-step development process for various orientations with respect to the direction of incident light. The highest diffraction efficiency was achieved for p-polarized light which propagates inside a medium of lower optical density and is outcoupled into a medium of higher optical density.

Collimation of diode laser beams with a single holographic diffractive element

Holographic diffractive optical elements collimating highly divergent, elliptical and astigmatic edge emitted diode laser beams are analyzed. Elements are recorded using only divergent beams with spherical wavefronts while off-axis astigmatism and coma of the holographic recording arrangement are compensated in a narrow beam approximation. Because of the very asymmetrical recording setup, significant blazing properties are present. Two types of the collimators are proposed: one for obliquely and the other for perpendicularly incident laser beam. Astigmatic properties of the output beams were measured in the reverse setup, i.e. when the collimated laser beams impinge on elements from their back side. Comparison of the advantages and drawbacks of both arrangements is presented.

Zone areas of diffractive phase elements producing focal annuli

A diffractive element which generates annular light source is investigated from the point of view of its area optimization. In the paraxial approximation, the zones distribution of such an element can be described by a double parabola. As the zone areas of this element are not the same, the equalization of first two zone areas is proposed in order to improve the diffraction efficiency.

Parameters of decentered Gaussian beams

A decentered Gaussian beam is a recently introduced generalization of an ordinary Gaussian beam, the propagation of both of which through an arbitrary centered paraxial optical elements can be described by ABCD matrices of paraxial optical rays. The paper shows that the M2 beam quality factor of the decentered Gaussian beam is the same as that of the ordinary Gaussian beam -- equal to 1. We further find out general conditions (for elements with pure real ABCD matrices) which must be fulfilled in order to accomplish the transformation of the Gaussian beam into decentered one or vice versa. The particular cases under specific conditions are presented in the work as well.

Fabrication and properties of light spiral filters

A simple technique of obtaining light spiral (helium) filters in UV exposed photoresist layers consisting in a combined use of binary masks and revolution of the photosensitive layers during exposition is presented. The filters investigated experimentally are inspected by observing intensity distribution in a laser beam reflected from the sample. The filter giving the angular phase shift variation which is close to that needed for the generation of the first order Bessel beam is realized.

Tandem of surface relief holographic gratings as a multiple-beam splitter

Abstract A new type of 1 × 9 multiple-beam splitter making use of two surface relief holographic gratings in stack is reported. The grating periods differ by a factor of three and the zero and ±1 diffraction orders generated by either grating on normal or slightly oblique incidence of a plane wave have nearly identical diffraction efficiencies. The fundamental feature of the design is the quoted ratio between grating periods rather than the specific choice of the profile shape. Splitters which generate nine beams (diffraction orders) bearing about 90% of the total output power with less than 4% non-uniformity in their diffraction efficiencies were achieved. Possible extension to 9 × 9 multiple-beam splitting using a tandem of crossed grating is addressed, too.