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hard-coated filters can be cleaned with acetone and are much more robust to changes in humidity.’ Fluorescence is relatively

inefficient; the protein will fluoresce in all directions but only that light passing through the eyepiece will be detected. Also, microscope optics will have some losses. ‘Because the process is relatively inefficient, a powerful laser light source is used to illuminate the sample,’ explains George. ‘Therefore, there’s a lot of excitation light contributing to the background noise that needs to be attenuated by the optics. Hard-coated filters are particularly advantageous as they are robust enough to handle the intense laser light sources.’

The latest technology

surrounding microscopy mean the optics have to work even harder. Super resolution microscopy techniques like PALM and STORM take advantage of photoactivation at different wavelengths to activate and deactivate different subsets of labelled proteins. ‘Traditionally, the dichroic mirror would only have to contend with a single laser wavelength,’ explains Jim Passalugo, product manager at Semrock, ‘whereas, with these techniques, the dichroic beam splitter has to have wider transmission and reflection bands to accommodate the various different excitation and emission wavelengths. This can be challenging when you want to maintain all the other properties of the mirror.’

Another big market for photonics in life sciences, according to Dr Matthias Schulze, director of marketing at Coherent, is flow cytometry, used in clinical applications such as testing blood samples of HIV sufferers. Flow cytometry requires a non-circular beam overlap to make the counts and beam shaping optics, such as a Powell lens, are often used to translate a Gaussian beam profile into a line or custom profile for flow cytometry equipment. Coherent provides beam shaping optics for flow cytometry applications. PLASMA FLUORESCENCE

‘The market is asking for a laser with integrated beam shaping optics,’ Schulze says. ‘By incorporating the beam shaping capabilities into the optics for the laser, instrument builders no longer have to do this themselves. The life science instrument community always wants to simplify complex subsystems from an engineering perspective.’

Coherent has also released the OBIS family of lasers, combining laser diode and OPSL solutions in the same package. OBIS lasers are suitable for flow cytometry, confocal microscopy, and DNA sequencing, among other applications. Schulze notes that DNA sequencing for patient care and personalised medicine is another important area for photonics

within life sciences. ‘Currently, the growth rate in DNA sequencing has been slow due to a variety of considerations surrounding the technology, such as data handling, but this could be very important market for photonics in the future,’ he says. ‘If disease treatment could be improved simply by sequencing a patient’s DNA, that will open the door to massive growth.’ l


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Miniature Spectrometers FEBRUARY 2012 l ELECTRO OPTICS 21

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