Structured Illumination, Laser Beam & Pulse Shaping

There have been many recent advances in light microscopy over the last decade as researchers try to overcome the resolution and diffraction limits to enable them to study nanoscale structures inside a cell without using an electron microscope. A new and powerful technique is in the field of Structured Illumination Microscopy which has advantages over other high resolution techniques: firstly, it has the ability to use multiple excitation wavelengths while not requiring any special fluorochrome, secondly, it is comparatively rapid in data acquisition and thirdly, the resolution of a fluoresence light microscope can be improved by a factor of two.

Structured illumination with pre-defined patterns is a promising approach in this field of research. By using a Spatial Light Modulator, patterns can be generated to achieve high resolution in imaging systems. This is particularly important in Neural activity imaging by using this type of structured illumination microscopy.

Spatial and temporal control of the neuronal activity needs sensitive and non-invasive methods together with precise and flexible light simulation patterns.Modification of optical wave-fronts is achieved using a Spatial Light Modulator by laser beamshaping, and by minimizing power loss, it allows the user to switch from one pattern to another with real 3D excitation volumes.

Application Examples

 

Laser beam shaping in waveguides

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 laser beam shaping in waveguides. The group have used the SLM for adaptive slit beam shaping in the creation of waveguides that allows an improvement in the fabrication of optical waveguides in bulk materials.

Please refer to this paper for background information: P. S. Salter, A. Jesacher, J. B. Spring, B. J. Metcalf, N. Thomas-Peter, R. D. Simmonds, N. K. Langford, I. A. Walmsley, and M. J. Booth, "Adaptive slit beam shaping for direct laser written waveguides," Opt. Lett. 37, 470-472 (2012)

The waveguide beam shaping image shows a waveguide type structure written in fused silica with a smoothly varying cross-section enabled by the adaptability of the SLM that allows more complicated structures to be fabricated than would be possible by using non-adaptive methods.

What is phase modulation? (high light utilization efficiency)

Cut the dark part from the whole power

Amplitude modulation
Device just cut the dark part from the whole power and just small portion of the incident light power can be utilized

Distribute the whole power

Phase modulation
Device modulates only phase and the modulated light has the same power to the incident light. The distributed light power is corresponding to the diffraction efficiency.

Application of laser beam forming

LCOS-SLM

High Speed by multi-point processing
Depth controllable
Simultaneous aberration correction

Lateral view of focusing beams

Application:
Laser material processing especially, inside the material with aberration correction in 3 dimensions
Laser marking / optical tweezers by multi-point generation and control
Structured illumination by highly efficient light distribution technique

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