Adaptive optics & ophthalmology

Adaptive optics is directly related to the improvement of the image quality. Prior to imaging onto a CCD camera, any non-plane wavefront can be flattened either by changing the optical path lengths with a deformable mirror as is often used in astronomy or by locally shifting the phase by using a phase only spatial light modulator.

Any intrinsic aberrations can be corrected in optical instruments such as microscopes. Used in the illumination pathway, SLMs allow perfect focusing in optical trapping setups (e.g. inside flow cells). Using this feature in combination with high power lasers enables the SLM to be used in the field of Laser Material Processing, e.g. inside glass, silicon or diamond.

The main adaptive optics application is in the field of Ophthalmology. Fascinating high resolution images of the human retina can be obtained as detailed below.

Application examples

 

Adaptive optics - material processing

Dr. Martin Booth, Department of Engineering Science, University of Oxford, UK

The images below show how powerful the use of an SLM can be in an experiment for fabrication in diamond using a dual adaptive optics system at a depth of 80 microns.

Please refer to this paper for background information: Richard D. Simmonds, Patrick S. Salter, Alexander Jesacher, and Martin J. Booth, "Three dimensional laser microfabrication in diamond using a dual adaptive optics system", Opt. Express 19, 24122-24128 (2011)

The left half of the below images use the SLM for aberration correction while the right half have the SLM set to a flat phase, which clearly show the advantages of using the SLM.

 

Ophthalmology

The upper image below shows an image of the retina without any correction being applied. The lower image shows the image of the retina after correction using the Hamamatsu LCOS-SLM.

 

The blood vessels can be clearly distinguished and it shows how powerful the Hamamatsu LCOS-SLM can be for ophthalmic imaging applications as further illustrated below showing images of the fundus both before and after correction:

Advantages SLM can offer and why

The benefits that Spatial Light Modulators offer in the field of adaptive optics are:

  • High number of controllable pixels in contrast to deformable mirrors which only offer a few actuators
  • Easy calculation of correction patterns for a wave front distortion due to individual pixels

 

Features of the Hamamatsu X10468 LCOS SLM series

Linear phase response and corrected wave front response Easy implementation, no calibration needed
High pixel fill factor resulting in high diffraction efficiency Fewer diffraction losses from the surface
High reflectivity up to 95% High efficiency
Very low phase noise Highly time-stable phase shifts
High laser powers can be irradiated onto the SLM chip 6Adaptive optics within Laser Material processing (e.g. marking inside high refractive index materials such as glass and diamond)
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