Axicons, Zinc Selenide

Overview
Beam Shape
Feedback
Prism Guide

Common Specifications
Substrate Material	Zinc Selenide^a
AR Coating Range	7 - 12 µm
Reflectance (per Surface)^b	R_avg < 1%; R_abs < 2%
Transmission^b	T_avg > 97%; T_abs > 92%
AR Coating Plot^c
Diameter	1" (25.4 mm)
Diameter Tolerance	+0.0 / -0.05 mm
Apex Rounding Diameter (S1)	<1.0 mm
Surface Quality (S1, S2)	60-40 Scratch-Dig
Surface Flatness (S2)	<λ/2 at 633 nm
Surface Deviation (RMS) (S1)	<0.07 µm
Surface Roughness (RMS) (S1,S2)	<20 Å
Clear Aperture (S1, S2)	>Ø22.86 mm
Edge Thickness	3.4 mm
Center Thickness Tolerance	±0.1 mm
Angular Tolerance	±0.01°

Click Link for Detailed Specifications on the Substrate Glass
Over AR Coating Range at 0° AOI
Coating data is available here.

Axicons Selection Guide
UV Fused Silica Axicons
ZnSe Axicons

Zemax Files
Click on the red Document icon next to the item numbers below to access the Zemax file download. Our entire Zemax Catalog is also available.

Click to Enlarge
The diagram above shows the definitions of thicknesses and angles used on this page.

Features

Transform a Collimated Beam into a Ring
Five Physical Angles Available: 0.1°, 0.2°, 0.5°, 1.0°, and 2.0°
Broadband AR Coating with R_avg <1% from 7 to 12 µm

An axicon, also known as a rotationally symmetric prism, is a lens that features one conical surface and one plano surface. They are commonly used to create a beam with a Bessel intensity profile or a conical, non-diverging beam. When converting a collimated beam into a ring, the plano side of the axicon should face the collimated source.

These axicons are offered with base angles from 0.1° to 2.0° and are precisely manufactured from zinc selenide (ZnSe), making them ideally suited for mid-infrared laser applications and for use with CO₂ laser applications, like materials processing. ZnSe axicons are offered with our -E3 antireflection coating for 7 to 12 µm. The coating is deposited on both sides of each optic in order to improve transmission by reducing surface reflections. Additionally, ZnSe axicons provide enough transmission in the visible region of the spectrum to allow the use of a red alignment beam, such as a HeNe laser.

An axicon deflects light according to Snell's Law, which can be used to find the deflection angle:

where n is the index of refraction of the glass, α is the physical angle of the prism, and ß is the angle the deflected beam creates with the optical axis. Here, the refractive index of air is assumed to be 1. This interaction is illustrated in the reference image to the right.

When handling optics, one should always wear gloves. This is especially true when working with zinc selenide, as it is a hazardous material. For your safety, please follow all proper precautions, including wearing gloves when handling these lenses and thoroughly washing your hands afterward. Due to the low hardness of ZnSe, additional care should be taken to not damage these lenses. Click here to download a PDF of the MSDS for ZnSe.

Thorlabs also offers Ø1/2" and Ø1" UV Fused Silica Axicons, either uncoated or with an AR coating, and with physical angles ranging from 0.5° to 40.0°.

Axicon Beams

Bessel Beam: Non-Diffracting
Ring-Shaped Beam: Ideal for Laser Drilling

Figure 1: The absolute value of a 0^th order Bessel function. A true Bessel Beam requires each ring to have the same energy as the central peak, thus an infinite amount of energy is needed.

A Bessel beam is a non-diffracting beam of concentric rings, each having the same power as the central ring. Technically, a Bessel beam cannot be created as it requires infinite energy. A beam closely resembling a Bessel distribution can be generated by passing a Gaussian beam through an axicon and taking the projection of the beam close to the axicon’s conical surface. The absolute value of a 0^th order Bessel function of the first kind is shown in Figure 1 (right).

When the beam is projected further from the lens, a single ring-shaped beam is formed. The beam is actually conical (i.e., diameter increases with distance), but the rays are non-diverging so that the thickness of the ring remains constant (see Figure 2). The ring's thickness will be half of the input laser beam's diameter. This type of beam is commonly used in laser-drilling applications.

Figure 2: Axicon ray tracing diagram.

Posted Comments:

Volker Franke (posted 2020-12-08 14:24:16.1)

ich habe eine optische Frage an Sie. Ich erstelle gerade Pläne für ein Angebot an einen Industriekunden in dessen Auftrag wir im Erfolgsfall Untersuchungen mit einem ringförmigen Laserstrahl machen wollen. Hierzu benötige ich aber zunächst eine Ein-/Abschätzung zur Machbarkeit. Wir wollen mit einem CO2-Laserstrahl einen relativ großen ringförmigen Fokus generieren. Hier die Eckpunkte zur Orientierung: - Ringdurchmesser Ziel ca. 40 mm - Rindbreite (Linienbreite) sollte möglichst klein sein (was geht?) (Wunsch wäre kleiner als 0,4 mm, besser 0,2 mm) - Arbeitsabstand zwischen Optik und Material sollte groß genug sein um die Optik vor Dreck zu schützen (gefühlt mindestens 100 mm) - Rohstrahldurchmesser ca. 16-18 mm - Geschätzte Laserstrahlleistung ca. 600 – 1500 W (das hängt sehr von der realisierten Ringbreite ab) Wie genau die Optik aufgebaut ist, spielt im Moment noch keine Rolle. Ich vermute man wird mindestens ein Axicon und eine Linse benötigen. Ob die Optiken transmittiv oder reflektiv sind, ist auch erst mal egal. Für erste Tests zur Machbarkeit wollen wir den Aufwand nicht zu groß werden lassen und könnten ggf. ein paar Abstriche von oben genannten Zielwerten machen, wenn dies mit Standardoptiken umsetzbar ist. Gern würde ich mich mit Ihnen austauschen, was machbar ist, damit ich unsere Arbeitspläne und das Angebot weiter ausarbeiten kann. Grundsätzlich denken wir als zweiten Lösungsweg auch darüber nach, das Ganze auch mit einem Faserlaser zu testen. Aufgrund der Absorption im Material wäre der CO2-Laser aber bevorzugt. Über Ihre Rückmeldung und technische Beratung würde ich mich sehr freuen. Mit freundlichen Grüßen Volker Franke

YLohia (posted 2020-12-08 11:20:43.0)

Hello, thank you for contacting Thorlabs. An applications engineer from our team in Germany (europe@thorlabs.com) will reach out to you directly to discuss this furter.

Selection Guide for Prisms

Thorlabs offers a wide variety of prisms, which can be used to reflect, invert, rotate, disperse, steer, and collimate light. For prisms and substrates not listed below, please contact Tech Support.

Beam Steering Prisms

Prism	Material	Deviation	Invert	Reverse or Rotate	Applications
Right Angle Prisms	N-BK7, UV Fused Silica, Calcium Fluoride, or Zinc Selenide	90°	90°	No	90° reflector used in optical systems such as telescopes and periscopes.
Right Angle Prisms	N-BK7, UV Fused Silica, Calcium Fluoride, or Zinc Selenide	180°	180°	No	180° reflector, independent of entrance beam angle. Acts as a non-reversing mirror and can be used in binocular configurations.
TIR Retroreflectors (Unmounted and Mounted) and Specular Retroreflectors (Unmounted and Mounted)	N-BK7	180°	180°	No	180° reflector, independent of entrance beam angle. Beam alignment and beam delivery. Substitute for mirror in applications where orientation is difficult to control.
Unmounted Penta Prisms and Mounted Penta Prisms	N-BK7	90°	No	No	90° reflector, without inversion or reversal of the beam profile. Can be used for alignment and optical tooling.
Roof Prisms	N-BK7	90°	90°	180^o Rotation	90° reflector, inverted and rotated (deflected left to right and top to bottom). Can be used for alignment and optical tooling.
Unmounted Dove Prisms and Mounted Dove Prisms	N-BK7	No	180°	2x Prism Rotation	Dove prisms may invert, reverse, or rotate an image based on which face the light is incident on. Prism in a beam rotator orientation.
Unmounted Dove Prisms and Mounted Dove Prisms	N-BK7	180°	180°	No	Prism acts as a non-reversing mirror. Same properties as a retroreflector or right angle (180° orientation) prism in an optical setup.
Wedge Prisms	N-BK7	Models Available from 2° to 10°	No	No	Beam steering applications. By rotating one wedged prism, light can be steered to trace the circle defined by 2 times the specified deviation angle.
Wedge Prisms	N-BK7	Models Available from 2° to 10°	No	No	Variable beam steering applications. When both wedges are rotated, the beam can be moved anywhere within the circle defined by 4 times the specified deviation angle.
Coupling Prisms	Rutile (TiO₂) or GGG	Variable^a	No	No	High index of refraction substrate used to couple light into films. Rutile used for n_film > 1.8 GGG used for n_film < 1.8

Depends on Angle of Incidence and Index of Refraction

Dispersive Prisms

Prism

Material

Deviation

Invert

Reverse or Rotate

Illustration

Applications

Equilateral Prisms

F2, N-SF11, Calcium Fluoride,
or Zinc Selenide

Variable^a

Dispersion prisms are a substitute for diffraction gratings.

Use to separate white light into visible spectrum.

Dispersion Compensating Prism Pairs

Fused Silica, Calcium Fluoride, SF10, or N-SF14

Variable Vertical Offset

Compensate for pulse broadening effects in ultrafast laser systems.

Can be used as an optical filter, for wavelength tuning, or dispersion compensation.

Pellin Broca Prisms

N-BK7,
UV Fused Silica,
or Calcium Fluoride

90°

Ideal for wavelength separation of a beam of light, output at 90°.

Used to separate harmonics of a laser or compensate for group velocity dispersion.

Depends on Angle of Incidence and Index of Refraction

Beam Manipulating Prisms

Prism

Material

Deviation

Invert

Reverse or Rotate

Illustration

Applications

Anamorphic Prism Pairs

N-KZFS8 or
N-SF11

Variable Vertical Offset

Variable magnification along one axis.

Collimating elliptical beams (e.g., laser diodes)

Converts an elliptical beam into a circular beam by magnifying or contracting the input beam in one axis.

Axicons

UV Fused Silica
or Zinc Selenide

Variable^a

Creates a conical, non-diverging beam with a Bessel intensity profile from a collimated source.

Depends on Prism Physical Angle

Polarization Altering Prisms

Prism	Material	Deviation	Invert	Reverse or Rotate	Applications
Glan-Taylor, Glan-Laser, and α-BBO Glan-Laser Polarizers	Glan-Taylor: Calcite Glan-Laser: α-BBO or Calcite	p-pol. - 0° s-pol. - 112°^a	No	No	Double prism configuration and birefringent calcite produce extremely pure linearly polarized light. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted.
Rutile Polarizers	Rutile (TiO₂)	s-pol. - 0° p-pol. absorbed by housing	No	No	Double prism configuration and birefringent rutile (TiO₂) produce extremely pure linearly polarized light. Total Internal Reflection of p-pol. at the gap between the prisms while s-pol. is transmitted.
Double Glan-Taylor Polarizers	Calcite	p-pol. - 0° s-pol. absorbed by housing	No	No	Triple prism configuration and birefringent calcite produce maximum polarized field over a large half angle. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted.
Glan Thompson Polarizers	Calcite	p-pol. - 0° s-pol. absorbed by housing	No	No	Double prism configuration and birefringent calcite produce a polarizer with the widest field of view while maintaining a high extinction ratio. Total Internal Reflection of s-pol. at the gap between the prism while p-pol. is transmitted.
Wollaston Prisms and Wollaston Polarizers	Quartz, Magnesium Fluoride, α-BBO, Calcite, Yttrium Orthovanadate	Symmetric p-pol. and s-pol. deviation angle	No	No	Double prism configuration and birefringent calcite produce the widest deviation angle of beam displacing polarizers. s-pol. and p-pol. deviate symmetrically from the prism. Wollaston prisms are used in spectrometers and polarization analyzers.
Rochon Prisms	Magnesium Fluoride or Yttrium Orthovanadate	Ordinary Ray: 0° Extraordinary Ray: deviation angle	No	No	Double prism configuration and birefringent MgF₂ or YVO₄ produce a small deviation angle with a high extinction ratio. Extraordinary ray deviates from the input beam's optical axis, while ordinary ray does not deviate.
Beam Displacing Prisms	Calcite	2.7 or 4.0 mm Beam Displacement	No	No	Single prism configuration and birefringent calcite separate an input beam into two orthogonally polarized output beams. s-pol. and p-pol. are displaced by 2.7 or 4.0 mm. Beam displacing prisms can be used as polarizing beamsplitters where 90^o separation is not possible.
Fresnel Rhomb Retarders	N-BK7	Linear to circular polarization Vertical Offset	No	No	λ/4 Fresnel Rhomb Retarder turns a linear input into circularly polarized output. Uniform λ/4 retardance over a wider wavelength range compared to birefringent wave plates.
Fresnel Rhomb Retarders	N-BK7	Rotates linearly polarized light 90°	No	No	λ/2 Fresnel Rhomb Retarder rotates linearly polarized light 90°. Uniform λ/2 retardance over a wider wavelength range compared to birefringent wave plates.