An axicon lens is a special lens with one plano (flat) surface and one conical surface. Also known as a rotationally symmetric prism, an axicon lens creates a focal line along the optical axis using interference, and can convert a laser beam into a ring shaped beam of light. Axicons are typically defined by their apex angles.
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At Shanghai Optics we produce high-precision axicon lenses for medical, scientific and industrial applications. From eye surgery to optical tweezers to laser drilling, from optical coherence tomography to particle physics, these prisms play a very important role in a wide range of optical systems.
To convert a collimated beam of light into a ring, one places the axicon lens with the flat side facing the collimated beam. Light enters at a perpendicular angle, in the center of this flat side, then travels along the axions optical axis and and leaves the lens as a cone of light. When projected onto a planar surface this light can be seen to be a ring. The closer the surface, the smaller the diameter of the ring.
While a Gaussian beam would deteriorate over distance, the beam profile produced by an axicon begins by nearly propagating the properties of a Bessel beam which maintains a stable intensity distribution as it propagates. In fact, it generates a very good approximation within its depth of focus, which can be calculated from the radius of the beam entering the axicon, the index of refraction of the axicon, and the angle α. If the angle of refraction is small, this can be approximated by radius/ (index of refraction-1) α.
Beyond the depth of focus, an axicon lens produces a uniform ring-shaped beam.
One application of axicons is in what is called optical trapping. This technique involves creating attractive and repulsive forces by means of a laser, then using these forces to mover or trap very small particles (micro particles) and, on occasion, cells. An axicon lens, forming a Bessel beam within the DOF (depth of focus, the beam overlap region), can effectively trap a particle on a flat surface such as a microscope slide.
Axicon lenses are also used for optical surgery, enabling the surgeon to focus in on an area of interest and to smooth tissue where necessary. For ultimate adjustability of ring diameter a combination of positive and negative axions are often used for this application.
In telescopes, lenses are used as solar concentrators to focus the light from the sun. In optical coherence tomography (OCT), they are used for laser drilling and optical trepanning.
A reflective axicon, also known as a reflaxicon, does not have the geometry of a traditional axicon. Rather, it consists of a pair of coaxial conical reflective surfaces. Designed to manipulate light in much the same manner of a transmissive axicon, it has several features that make it the best choice in some situations: a high damage threshold, low chromatic aberration, and better group velocity dispersion.
At Shanghai Optics we produce a variety of axicon lenses from optical materials such as fused silica, sapphire, ZnSe, and plastics. Our lenses can be made with almost any ring diameter, and both refractive and diffractive axicon lenses are available. We can also design optical assemblies such as a combination of axicons with beam expanders, lenses, or additional axions to produce your desired beam profile.
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Substrate Material UV Fused Silica Diameter 12.7mm / 25.4mm / 50.8mm Diameter Tolerance +/-0.05mm Thickness Tolerance +/-0.05mm Surface Quality (S1,S2) 40-20 Scratch-Dig Surface Deviation (RMS)(S1) <0.05μm Surface Irregularity (S2) λ/10@633nm Surface Irregularity λ/4@632nm Clear Aperture (S1, S2) &#;90% of Central Diameter Angle Tolerance ±3 arcmin Centering Tolerance <1 armin Surface Roughness (S1) 0.5nmContact us today for assistance with your custom axicon lens project.
An axicon is a specialized type of lens that has a conical surface. An axicon transforms a laser beam into a ring shaped distribution.[1] They can be convex or concave and be made of any optical material. The combination with other axicons or lenses allows a wide variety of beam patterns to be generated. It can be used to turn a Gaussian beam into a non-diffractive Bessel-like beam.[2] Axicons were first proposed in by John McLeod.[3]
Axicons are used in atomic traps and for generating plasma in wakefield accelerators.[4] They are used in eye surgery in cases where a ring-shaped spot is useful.
The Axicon is usually characterized by the ratio of the diameter of the ring to the distance from the lens tip to image plane d/l.
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Single axicons are usually used to generate an annular light distribution which is laterally constant along the optical axis over a certain range. This special feature results from the generation of (non-diffracting) Bessel-like beams with properties mainly determined by the Axicon angle α.
Creation of Bessel beams through an axiconThere are two areas of interest for a variety of applications: a long range with an almost constant intensity distribution (a) and a ring-shaped distant field intensity distribution (b). The distance (a) depends on the angle α of the Axicon and the diameter (ØEP) of the incident beam. The diameter of the annular distant field intensity distribution (b) is proportional to the length l. The width of the ring is about half the diameter of the incident beam.[5]
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One application of axicons is in telescopes, where the usual spherical objective is replaced by an axicon.[3] Such a telescope can be simultaneously in focus for targets at distances from less than a meter to infinity, without making any adjustments. It can be used to simultaneously view two or more small sources placed along the line of sight.
Axicons can be used in laser eye surgery. Their ability to focus a laser beam into a ring is useful in surgery for smoothing and ablating corneal tissue. Using a combination of positive and negative axicons, the diameter of the ring of light can be adjusted to obtain the best performance.[6]
Axicons are also used in optical trapping.[6] The ring of light creates attractive and repulsive forces which can trap and hold microparticles and cells in the center of the ring.
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The reflective axicon or "reflaxicon" was described in by W. R. Edmonds.[7] The reflaxicon uses a pair of coaxial, conical reflecting surfaces to duplicate the functionality of the transmissive axicon. The use of reflection rather than transmission improves the damage threshold, chromatic aberration, and group velocity dispersion compared to conventional axicons.
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In research at Physikalisch-Chemisches-Institut, Heidelberg, Germany, axicon lenses have been used in laser diagnostics of mechanical properties of thin films and solids by surface-wave spectroscopy.[3] In these experiments, laser radiation is focused on the surfaces in a concentric ring. The laser pulse generates concentric surface acoustic waves, with amplitude that reaches a maximum in the center of the ring. This approach makes it possible to study mechanical properties of materials under extreme conditions.
Axicons have been used by the research team at Beckman Laser Institute and Medical Clinic to focus a parallel beam into a beam with long focus depth and a highly confined lateral spot, to develop a novel optical coherence tomography (OCT) system.[3]
Inphase Technologies researchers use axicons in holographic data storage. Their goal is to determine the effects of axicons on the Fourier distribution of random binary data spectrum of a spatial light modulator (SLM).
Wendell T. Hill, III's research group at the University of Maryland is focused on creating elements of atom optics, such as beam splitters and beam switches, out of hollow laser beams.[3] These beams, made using axicons, provide an ideal optical trap to channel cold atoms.
An article published by the research team at St. Andrews University in the UK in the Sept. 12 issue of Nature describes axicon use in optical tweezers, which are commonly used for manipulating microscopic particles such as cells and colloids.[8] The tweezers use lasers with a Bessel beam profile produced by illuminating an axicon with a Gaussian beam, which can trap several particles along the beam's axis.
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