Invariant propagation of uniform-intensity Schell-model fields

Propagation of partially coherent uniform-intensity Schell-model fields in a uniform dielectric medium is considered. It is first established that the spatial frequencies contained in such a field are non-correlated. Then it is shown that the distribution of the complex degree of spatial coherence associated with any such field is propagation invariant. An experimental set-up consisting of a diffractive beam-shaping element, a rotating diffuser, an aperture and a lens is suggested for the generation of transversely confined approximations of a large class of propagation-invariant Schell-model fields.     

Two-element diffractive systems for generation of Bessel fields

We demonstrate experimentally a combination of two apodizing diffractive elements, which generate nearly propagation-invariant Bessel fields efficiently with almost uniform axial intensity distributions over the specified region recently introduced by two of the present authors. Strongly reduced intensity fluctuations near both ends of the propagation-invariant range are verified. Various design and alignment issues of the two-element systrem are addressed numerically.     

New Design of High NA Photolithographic Lens Using Diffractive Optical Element

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Replication of continuous-profiled micro-optical elements for silicon integration

A novel scheme for the integration of diffractive optical elements onto silicon is presented. The processing is made in reverse order, meaning that the process of structuring the optical elements on the wafer precedes the silicon microstructuring. The first processing step on the wafer is the hot embossing of the optical microstructures into an amorphous fluorocarbon polymer spin coated on the wafer. The cured polymer forms a highly stable material with excellent optical properties. The remaining silicon processing is thus performed with the diffractive optical elements already in place. Two different diffractive structures were used in the development of the method-a (Fresnel) lens with a rather low f-number and a diffractive element producing a fan-out of a large number of paraxial beams.     

Achromatic hybrid refractive-diffractive lens with extended depth of focus

A method for designing achromatic hybrid refractive-diffractive elements that can produce beams with long focal depths while they preserve the entire aperture for capture of light and high transverse resolution is presented. Its working principle is based on the combination of a diffractive optical element that generates a long range of pseudonondiffractive rays and a refractive lens of opposite dispersion to form an achromatic hybrid lens. A hybrid lens with a fast f-number (f/1) that works in the entire visible wave band (400-700 nm) was designed and fabricated. Simulation results demonstrate a factor-of-10 improvement in depth of focus compared with that of a conventional f/1 lens, with matching 1-microm lateral resolution. Experimental results confirm the effectiveness of the proposed method through demonstration of an achromatic hybrid lens with better than a factor-of-7 improvement in depth of focus and 1-microm transverse resolution.     

Integrated diffractive andrefractive elements for spectrum shaping

Diffractive elements can be designed for spectrum shaping in the Fourier or Fresnel plane by iterative methods. It is necessary to use a Fourier lens and the wavelength for which the diffractive elements were designed to get the required spectrum shaping at the Fourier plane. Using a different wavelength will cause chromatic aberration. We deal with the combination of refractive and diffractive elements and two or more different diffractive elements on the same element to get appropriate beam shaping of light sources with a multiple spectral output. Simulations are preformed that transform the profile of a He-Ne laser with a Nd:YAG laser source, and shape the trapezoidal beam profile of an excimer laser into a Gaussian beam is also considered.     

Self-healing property of a caustic optical beam

It is well known that Bessel beams and the other families of propagation-invariant optical fields have the property of self-healing when obstructed by an opaque object. Here it is shown that there exists another kind of field distribution that can have an analog property. In particular, we demonstrate that a class of caustic wave fields, whose transverse intensity patterns change on propagation, when perturbed by an opaque object can reappear at a further plane as if they had not been obstructed. The physics of the phenomenon is fully explained and shown to be related to that of self-healing propagation invariant optical fields.     

Diffraction characteristics of optical elements designed as phase layers with cosine-profiled periodicity in the azimuthal direction

The article concerns an investigation of the Fresnel diffraction characteristics of two types of phase optical elements under Gaussian laser beam illumination. Both elements provide an azimuthal periodicity of the phase retardation. The first element possesses azimuthal cosine-profiled phase changes deposited on a plane base. The second element is a combination of the first element and a thin phase axicon. The cosine profile of the phase retardation of both diffractive elements produces an azimuthal cosine-profiled modulation on their diffractograms. It destroys the vortex characteristics of their diffraction fields.     

Mode-matched phase diffractive optical element for detecting laser modes with spiral phases

A new type of diffractive optical element for detecting and measuring the power distribution of transverse modes emanating from radially symmetric laser resonators is presented. It is based on a relatively simple straightforward design of a phase-only diffractive optical element that serves as a matched filter, which correlates between specific prerecorded transverse modes with a certain azimuthal mode order and those in the incident laser light. Computer simulations supported by experimental results demonstrate how such elements can accurately detect modes with spiral phases and provide quantitative results on the modal power distribution.     

Regenerative ring-laser design by use of an intracavity diffractive mode-selecting element

We report what we believe to be the first application of diffractive phase elements for transverse mode selection in laser ring resonators. We show that this resonator type offers several advantages over Fabry-Pérot resonators with diffractive mirrors. The design for a regenerative ring resonator that produces an eighth-order super-Gaussian intensity profile beam is presented. Numerical simulations, including modeling of the gain saturation and experimental tests, have been carried out to demonstrate the performance of this approach for cw and pulsed operations.     

Analytic design and solutions for resonance domain diffractive optical elements

A model for designing and analyzing complicated surface relief diffractive elements in the resonance domain is developed. It is based on subdividing the complicated diffractive element into many highly efficient local diffraction gratings whose surface relief modulations can be effectively characterized as slanted volume gratings for which closed form analytic solutions exist. The model is illustrated by finding in the resonance domain the local period, effective slant angle, and groove depth at each location on an off-axis cylindrical diffractive lens.     

对衍射光学元件温度特性的研究

大多数空间光学仪器的工作环境温度变化范围都较大。对折射元件和衍射元件的温度特性进行了分析,建立了透镜焦距和衍射效率随环境温度的变化关系,并论述了利用衍射光学元件的温度特性实现光学系统消热差的原理和设计方法。     

Spectral properties of multiorder diffractive lenses

Diffractive lenses have been traditionally designed with the first diffracted order. The spectral characteristics of diffractive lenses operating in higher diffracted orders differ significantly from the first-order case. Multiorder diffractive lenses offer a new degree of freedom in the design of broadband and multispectral optical systems that include diffractive optical elements. It is shown that blazing the surface-relief diffractive lens for higher diffraction orders enables the design of achromatic and apochromatic singlets. The wavelength-dependent optical transfer function and the associated Strehl ratio are derived for multiorder diffractive lenses. Experiments that illustrate lens performance in two spectral bands are described, and the results show excellent agreement with the theoretical predictions.     

On propagation-invariant and self-imaging intensity distributions of electromagnetic fields

Propagation-invariant azimuthally and radially polarized fields are examined. The orthogonality of these fields in every point of space is used to form propagation-invariant intensity distributions outside the scope of scalar theory. The same principle is then used to form self-imaging electromagnetic fields with non-self-imaging scalar components.     

二元光学折/衍混合消色差望远物镜设计

首先从光栅衍射理论出发导出衍射光学元件的色散公式，并进一步推导出用一种材料进行折／衍混合消色差望远物镜设计的公式。最后给出全折射型、一个混合型消色差和一个改进型消色差望远物镜的例子，并进行了比较。结果说明，混合型透镜的性能优于全折射型透镜，而改进型消色差物镜的总体性能优于原混合消色差物镜     

Diffractive-refractive behavior of kinoform lenses

The connection between the diffractive behavior and the refractive behavior of kinoform lenses is investigated. The image-forming capabilities of the diffractive element are found to be expressed as an interference pattern that is due to a set of associated refractive lenses corresponding to each zone of the kinoform. The coefficient modulating the contribution of each refracting zone is determined. The term linking the point-spread function of a refractive lens and a diffractive lens is also obtained. Spectral and spatial aspects are compared as the diffractive element approaches the refractive limit.     

Binary phase zone-plate arrays for laser-beam spatial-intensity distribution conversion

We report on the theory and development of a diffractive element composed of a binary phase zone-plate array. This component conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently (82%) a flattop intensity envelope on target. Analysis of the design indicates that manufacturing tolerances are not critical. Experimental performances on target from x-ray emission and shock-breakout measurements are also presented.     

Propagation-invariant beams in uniaxial crystals

Propagation-invariant electromagnetic beams, propagating along the optical axis of a uniaxially anisotropic crystal, are investigated. The beams are a superposition of propagation-invariant ordinary and extraordinary fields, with different polarizations states and Bessel profiles. The analytical expression of the Poynting vector reveals an azimuthal transverse energy flow that becomes pure longitudinal, if the complex amplitudes of the ordinary and extraordinary fields are either in phase or in phase opposition.     

Application of holographic diffractive doublets as collimators for highly elliptical light beams edge emitted from diode lasers

Two schemes for collimation of diode laser light beams with high cross-sectional ellipticity by means of a doublet of holographic diffractive elements are proposed and designed; one of the schemes is realized and tested. In both the schemes the first element of the doublet collimates the beam in the plane of the longer axis of the ellipse, and the second element collimates it in the perpendicular plane. Each element simulates a cylindrical lens. The set-up with the focal line of the cylindrical beam oriented perpendicular to the meridional plane is realized experimentally. The elements are holographic surface-relief gratings recorded in photoresist. For recording, only homocentric diverging beams are used, which minimizes potential aberrations and optical dirt. The parameters of the elements are computed using four equations, including one equation for compensation of the aberration of the lowest order. The doublet is proposed for the He—Ne red wavelength. A collimated He—Ne laser beam is employed for quality testing of collimation in a reverse way, with this beam impinging upon the second element. Characteristics of an outgoing beam from the first element of the doublet are recorded with a charge-coupled device camera. Calculated spot diagrams are compared with cylindrical focal lines captured separately from both the elements.