Design and manufacture of diffractive
optical elements

Optical mode converter & π phase-plate

Hermite-Gauss mode conversion

Introduction

Arbitrary solutions of the paraxial Helmholtz equation can be expressed as combinations of Hermite-Gaussian modes (whose amplitude profiles are separable in x and y using Cartesian coordinates).

For many applications, it is useful to convert the fundamental laser mode TEM00 to a higher order of Hermite-Gaussian beams:


Phase ElementOutput IntensityPhase ElementOutput Intensity
TEM00TEM00 Phase ElementTEM00 Output IntensityTEM20TEM20 Phase ElementTEM20 Output Intensity
TEM01TEM01 Phase ElementTEM01 Output IntensityTEM12TEM12 Phase ElementTEM12 Output Intensity
TEM10TEM10 Phase ElementTEM10 Output IntensityTEM21TEM21 Phase ElementTEM21 Output Intensity
TEM11TEM11 Phase ElementTEM02 Output IntensityTEM22TEM22 Phase ElementTEM22 Output Intensity
TEM02TEM02 Phase ElementTEM02 Output Intensity

Each mode HGlm is denoted by two indices, l & m, which represent the number of modes in the x & y directions, respectively.

Typical Applications
  • Communication
  • Scientific & research
  • Scanning applications
  • STED microscopy
  • Optical tweezing
  • Optical trapping
Features
  • Aberration free
  • High efficiency
Typical Optical set-up: Typical Operating Principle
Optical set-up

The operating principle is quite straight-forward - a Fourier Transform (FT) is applied on the initial field amplitude and phase to obtain the desired field (or intensity) at far-field. In this way, the fundamental Gaussian beam TEM_00 is converted to a higher order of Hermite-Gaussian modes. For example - conversion of TEM_00 to TEM_10:

Operation Principle

For the phase-plate element, the height of the step is defined as:

Mode Convertor

where n is the refractive index of the material.

Design Considerations:

For a high-quality performance, the laser output should be Single Mode (TEM00 with an M2 value <1.3. If the M2 is larger, it may still be possible to reduce the M2 value by inserting a spatial filter in between the laser and the DOE lens component.

All optics in the beam path should be of high quality, i.e. have a low irregularity figure, in order not to introdcue wav-front errors which would degrade the diffractive phase element's performance.


General Specifications:

Materials: Fused Silica, Sapphire, ZnSe, Plastics
Wavelength range: 193[nm] to 10.6[μm]
DOE design: Binary (2-level)
Element size: Few mm to 100 [mm]
Coating (optional): AR/AR Coating
Custom Design: Available

π Phase-Plate

Introduction:

For many applications, it is necessary to use a phase element with a π-phase at the center. For imaging purposes using this element will result in an increased depth-of-focus, and for particle manipulation purpose, using this element will result in optical tweezing\trapping.

Pi Phase Plate

Standard Products:

Part Number Diameter [mm] Aperture size [mm] Material Description
PE-202 25.4 23.6 Fused Silica Half-space π difference mode
converter, TEM01 (or TEM10)
PE-230 25.4 23.6 Fused Silica Quarter-space π difference
mode converter, TEM11
PE-215 11 9.2 Fused Silica Round π phase at the center,
diameter 4817 μm
PE-216 25.4 23.6 Fused Silica Round π phase at the center,
diameter 5680 μm
PE-217 20 23.6 Fused Silica Round π phase at the center,
diameter 6200 μm
PE-218 25.4 18.2 Fused Silica Round π phase at the center,
diameter 8428 μm
PE-219 25.4 23.6 Fused Silica Round π phase at the center,
diameter 10838 μm
PE-220 25.4 23.6 Fused Silica Round π phase at the center,
diameter 7224 μm
PE-221 11 9.2 Fused Silica Round π phase at the center,
diameter 3612 μm
PE-222 11 9.2 Fused Silica Round π phase at the center,
diameter 4214 μm
PE-223 11 9.2 Fused Silica Round π phase at the center,
diameter 3000 μm
PE-224 11 9.2 Fused Silica Round π phase at the center,
diameter 5400 μm
PE-225 25.4 23.6 Fused Silica Round π phase at the center,
diameter 6384 μm
PE-226 12.5 10.7 Fused Silica Round π phase at the center,
diameter 6840 μm
PE-227 25.4 23.6 Fused Silica Round π phase at the center,
diameter 8900 μm
PE-228 11 9.2 Fused Silica Round π phase at the center,
diameter 1200 μm
PE-229 11 9.2 Fused Silica Round π phase at the center,
diameter 1800 μm

For a quotation of an above Part Number, please specify the wavelength used.

Contact us for more information or for a custom solution.

References:

@Copyright 2017, Holo/Or Ltd. P.O.B 1051, Rehovot, 7611001 Israel
Phone: +972-89409687/8, Fax: +972-89409606

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