Beam Expanders Enable the Investigation of Inner City Pollution

Topics Covered

Introduction
Key Features of High Throughput Achromatic Beam Expanders
Specifications of Laser Beam Expanders
Applications of Laser Beam Expanders
Role of OSL Beam Expanders in Monitoring Inner City Atmospheric Pollution
About Optical Surfaces

Introduction

The beam expanders offered by Optical Surfaces are composed of off-axis mirrors, which provide a highly efficient transmission and an unhindered output. Beam expanders are an ideal optical instrument to produce an expanded collimated output beam by increasing the diameter of a collimated input beam. Beam expanders are employed in applications, including remote sensing, LIDAR systems, interferometry, laser scanning, and high power lasers. 

Key Features of High Throughput Achromatic Beam Expanders

OSL Beam Expanders (Figure 1) are suitable for applications demanding the formation of a small spot at some distance from the laser or extended collimation range for illumination or alignment of distant objects. They are available in both standard (5x, 10x, 15x and 20x fixed magnification) customer specified (fixed or variable magnification) configurations. OSL beam expanders are user-friendly and expand any collimated input light source accurately without any obstruction.

Figure 1. High Throughput Achromatic Beam Expanders. 

OSL Beam Expanders’ reflective design is achromatic. With aluminum coatings, OSL Beam Expanders are capable of operating from UV to far IR devoid of adjustment. They are portable and can be utilized without the requirement for internal re-alignment. Each OSL beam expander is offered in aluminum housing with provision to be fixed to an optical table. Accurate beam pointing is ensured with alignment aids.

With a surface accuracy of better than λ/5, the off-axis design of OSL Beam Expanders generates no central obscuration, yielding highly efficient transmission unaffected by spider diffraction patterns. Optical Surfaces supplies an interferogram and OPD map with each beam expander. The ISO 9001-2000-accredited production facility of Optical Surfaces offers the flexible resources to supply from single specialist requirements to OEM quantities.

Specifications of Laser Beam Expanders

The following are the specifications of laser beam expanders:

  • Wavefront accuracy > λ/5 p-v at 633nm
  • Standard apertures up to 300mm
  • Vertical or horizontal beam separation
  • Expansion up to x100
  • Wide choice of coatings
  • Temperature stabilisation using Invar tie bars (option)
  • Common focus design (option)
  • Variable magnification (option)
  • Cleanroom assembly (option)
  • Focusing capability (option)
  • Vacuum compatibility (option).

Applications of Laser Beam Expanders

The following are the applications of laser beam expanders:

  • High power lasers
  • Interferometers
  • Remote sensing
  • LIDAR systems requiring fixed or variable focusing mechanism
  • Doppler – shift LIDAR.

Role of OSL Beam Expanders in Monitoring Inner City Atmospheric Pollution

In partnership with the Remote Sensing Group at the Defence Evaluation and Research Agency (D.E.R.A., Malvern, UK) and the Civil Engineering Department of Salford University (Manchester, UK), Optical Surfaces developed high performance off-axis beam expanders for a new generation of pulsed coherent LIDAR systems. The LIDAR system was intended to quantify phenomena involved in local wind fields and the distribution of atmospheric pollution in built up city areas.

Based on over three decades of international design and production expertise, Optical Surfaces proposed the use of an off-axis parabolic beam expander to achieve the required high performance and design compactness. The stabilized production environment of Optical Surfaces enabled it to provide a compact x15 off-axis beam expander unit with λ/5 transmitted wavefront accuracy over the entire 150mm output aperture measured at 633nm. The performance limitation of the LDIAR system caused by telescope feedback is virtually eliminated, thanks to the high surface quality of the optics supplied.

The ready aligned variable focus (infinity to 20m) beam expanders were integrated into the LIDAR unit easily and rapidly. Moreover, future operational flexibility was incorporated as the off-axis beam expander design provided completely achromatic performance from the infrared to the visible. Operating at 120 pulses per second (500ns pulse length) the DERA LIDAR system can routinely monitor the aerosol concentration and wind velocity, covering a range of 3km with a range resolution of roughly 100m.

About Optical Surfaces

Optical Surfaces Ltd, has been producing optical components and systems for more than 30 years and is now accepted as one of Europe's leading manufacturers of high-precision optics. Our list of products include:

  • Etalons and Windows
  • Off-Axis Mirrors
  • Laser Beam Expanders
  • Collimators
  • Lenses and Prisms
  • Sphericals and Flat Mirrors
  • Mounted/Custom Optics.

The main workshops and test facilities are deep underground in a series of tunnels excavated in solid chalk where temperature remains constant and vibration is practically non-existent. With such stable conditions testing particularly with long path lengths become quantifiable and reliable.

Working with these natural advantages is a highly skilled team of craftsmen with a commitment to excellence in both product quality and customer service.

Interferometers routinely used include Zygo, Twyman Green, Scatterplate, Fizeau up to 600mm dia. Laser unequal path (LUPI) and point diffraction. They are able to test surface geometry, interfacing with our Wyko computer fringe analysis to confirm final wavefront.

This information has been sourced, reviewed and adapted from materials provided by Optical Surfaces.

For more information on this source, please visit Optical Surfaces.

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