Axicon is a versatile optical element for forming a zero-order Bessel beam, including high-power laser radiation schemes. Nevertheless, it has drawbacks such as the produced beam’s parameters being dependent on a particular element, the output beam’s intensity distribution being dependent on the quality of element manufacturing, and uneven axial intensity distribution. To address these issues, extensive research has been undertaken to develop nondiffracting beams using a variety of advanced techniques. We looked at four different and special approaches for creating nondiffracting beams in this article. Diffractive axicons, meta-axicons-flat optics, spatial light modulators, and photonic integrated circuit-based axicons are among these approaches. Lately, there has been noteworthy curiosity in reducing the thickness and weight of axicons by exploiting diffraction. Meta-axicons, which are ultrathin flat optical elements made up of metasurfaces built up of arrays of subwavelength optical antennas, are one way to address such needs. In addition, when compared to their traditional refractive and diffractive equivalents, meta-axicons have a number of distinguishing advantages, including aberration correction, active tunability, and semi-transparency. This paper is not intended to be a critique of any method. We have outlined the most recent advancements in this field and let readers determine which approach best meets their needs based on the ease of fabrication and utilization. Moreover, one section is devoted to applications of axicons utilized as sensors of optical properties of devices and elements as well as singular beams states and wavefront features.

Modern Types of Axicons: New Functions and Applications.

The invention discloses a method and device for measuring microstructure morphology based on spectral modulation depth coding. An element to be measured and a spatial light modulator are conjugated atthe center wavelength of the spectral range used in the measurement; a beam folding coupler, the spatial light modulator, a collimating and expanding lens, a beam splitter, an axial non-achromatic microscope objective lens, an imaging lens and a color camera are in a common optical path structure. During the measurement, the pre-calibration of the corresponding relation of the 'spectral-depth' isfirstly carried out on a system device, and each frame monochromatic shift-phase fringe pattern reflected by the element to be measured is acquired by a measuring device, so as to obtain the modulation depth distribution of each monochromatic light fringe pattern related to the surface shape of the element to be measured, and the coded image is obtained; the 'spectrum-modulation depth' relation curve of each point on the surface to be measured is determined by using Gaussian, quasi-Gaussian or spline model fitting, the depth information of each point on the surface to be measured is demodulated, and the fast and precise measurement of the microstructure topography of the three-dimensional topography distribution of the element to tested, without mechanical scanning or contact, is completed.

Method and device for measuring microstructure morphology based on spectral modulation depth coding

The invention discloses a micro-structure morphology measurement method and device based on dispersion spectrum coding. According to the method and the device, a compound color sinusoidal fringe parallel light passes through an axial dispersion type optical system, then is sequentially dispersed in the axial direction and is focused on different axial depth positions in a one-to-one correspondencemode, the modulation degree of each single-color sinusoidal fringe of the axial dispersion changes along with the axial depth and reaches a maximum value near the focal plane position, so that a unique code among spectrum-modulation degree-depth required by measurement is established, and non-mechanical scanning, full-field non-contact and rapid (dynamic and even transient) high-precision measurement of the three-dimensional morphology distribution of a tested element can be realized only with multiple frames (such as three frames) of phase-shift (or single-frame) dispersion spectrum coded images.

Micro-structure morphology measurement method and device based on dispersion spectrum coding

Generation of Mathieu beams based on the detour phase encoding method

The invention belongs to the technical field of optics, and particularly relates to a spatial phase shift dynamic interferometer based on a liquid crystal spatial light modulator and application of the spatial phase shift dynamic interferometer. The spatial phase shift dynamic interferometer based on the liquid crystal spatial light modulator comprises a He-Ne laser, a first pinhole filtering, a first collimation and beam expanding system, a lambda/2 wave plate, a polarizing beamsplitting prism, a first lambda/4 wave plate, a second collimation and beam expanding system, a second pinhole filtering, a polarizing film, the liquid crystal spatial light modulator, a second lambda/4 wave plate, a standard spherical mirror, a measured mirror, a polarization analyzer, an imaging system, a third pinhole filtering and an optical detector, dynamic testing of an aspheric surface member and a free-form surface member is realized through coded modulation of SLM, the SLM is used for replacing a tinypolarization phase shift array to realize spatial phase modulation, the adjustment is simple, the tiny polarization phase shift array is not required, and the difficulty is greatly reduced. Accordingto the spatial phase shift dynamic interferometer based on the liquid crystal spatial light modulator and application of the spatial phase shift dynamic interferometer, the function of real-time dynamic display is achieved, low energy consumption, easy control and high speed are achieved, the spatial resolution ratio is easier to improve, and high-precision measurement is realized.

Spatial phase shift dynamic interferometer based on liquid crystal spatial light modulator and application of spatial phase shift dynamic interferometer

Axicon is an interesting optical element for its optical properties. This paper presents an approach to dynamically generated tunable axicons with a spatial light modulator (SLM). 256-level phase computer-generated holograms (CGHs) were loaded into the SLM to simulate the positive and negative axicons. The intensity distributions of beams passing through these axicons were analyzed with the principle of blazed grating and Fresnel diffraction; and the diffraction patterns were obtained theoretically in terms of zero-order Bessel beams and annular hollow beams, corresponding to the positive and negative axicons, respectively. Experimental results verified that the diffraction patterns have the same distribution as the real axicon. The types of the axicon and the axicon’s parameters can be easily altered through changing the CGHs.

Tunable Axicons Generated by Spatial Light Modulator with High-Level Phase Computer-Generated Holograms

The invention discloses a cross-scale surface topography measurement device and method based on optical phase shift. The device comprises a computer, a light intensity controllable white light source, a first lens, a filter rotating disk, a beam splitting prism, a second lens, a third lens, a CCD (Charge Coupled Device) camera, a spatial light modulator (SLM) and a fourth lens. Accurate optical phase shift is realized by the pure phase modulation type liquid crystal SLM, four kinds of monochromatic light having consistent light intensity distribution are obtained by the light intensity adjustable white light source and four band pass filters, and the measurement range is expanded via reasonable size engagement by using the principle of multi-wavelength interference. In repeated optical phase shift, interferential image series of different wavelengths are acquired in a manner of alternating the filters, and point-by-point and frame-by-frame phase operation is performed by using an optimized four-step phase shift method to obtain the height of a topography point within a large scale range. The device and the method can meet the requirement of cross-scale measurement range and keep the nano precision of single-wavelength interference, and have important application value.

Cross-scale surface topography measurement device and method based on optical phase shift

Surface morphology measurement based on multiple wavelengths interferometric theory has been widely used, and the alignment error of initial phase of different wavelengths can influence the measurement accuracy. A phase shift method to drive the piezoelectric transducer (PZT) by zigzag with a fallback path is proposed, which can overcome the hysteresis and creep behavior of the PZT before switching to different wavelengths. The ellipse fitting and unwrapping algorithms are applied to extract phase-shifts from interferograms. The starting points of different wavelengths are aligned according to the displacement and movement direction of PZT. The experimental results show that the presented method can improve the aligned accuracy of the initial position during multiple-wavelength microscopic interferometry measurement.

Alignment of the initial phase during multiple-wavelength switching in microscopic interferometry

High-order Bessel beams are widely used in laser processing and precision measurement. For the realization of high-order Bessel beams, a spatial light modulator is used to load the high-order phase hologram instead of the real spiral phase plate and the axicon. The distribution of light field in two modes of axicon combination and phase superposition is analyzed theoretically. The beam modulation in two modes is designed and compared experimentally. The results show that the modulation effect of the phase superposition method is better than that of the axicon combination method. Meanwhile, the operation is flexible and the manufacture errors can be reduced. It is an effective method for realizing high-order Bessel beams.

Realizing High-order Bessel Vortex Beams with High-level Phase Holograms

The invention relates to a non-diffracting photomoire fringe center positioning method and system. The method comprises the following steps: step 1, carrying out image preprocessing on non-diffractingoptical moire fringes containing noise, and extracting a local concentric annulus region; Step 2, carrying out a series of morphological processing on the image processed in the step 1; Step 3, carrying out local concentric annulus detection on the image processed in the step 2; And step 4, for the image processed in the step 3, performing clustering analysis on the initial circle center set, deleting abnormal points in the two groups of circle center sets after clustering, and iteratively solving the center points of the two groups of circle center sets to realize diffraction-free optical moire fringe positioning. The device can position the centers of the two light spots of the non-diffracting photomoire fringes at the same time, is high in automation degree, high in positioning precision and wide in application range, and has good application prospects.

Cheng Zhuang

Papers

Tunable Axicons Generated by Spatial Light Modulator with High-Level Phase Computer-Generated Holograms

Cross-scale surface topography measurement device and method based on optical phase shift

Alignment of the initial phase during multiple-wavelength switching in microscopic interferometry

Realizing High-order Bessel Vortex Beams with High-level Phase Holograms

non-diffracting photomoire fringe center positioning method and system