FEATURE ULTRAFAST LASERS
‘With femtosecond laser surgery, the process speed is relatively slow, and is impractical for appreciable tissue removal’
Shephard and his colleagues have
therefore developed hollow core fibres for picosecond lasers in this application. They are mechanically and chemically robust, biocompatible, with very low sensitivity to bending, he said. ‘Hollow core fibres allow single mode
Members of Professor Goutam Samanta’s research group at the Photonic Sciences Lab, Physical Research Laboratory, in Ahmedabad, India. From left, Dr Varun Sharma, Subith Kumar, Professor Samanta, Anirban Ghosh, Ravi Saripalli, Vimlesh Kumar, Dr Deepika Yadav (inset)
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‘producing protons, but still there is some work to be done on the characteristics of these protons,’ Courjaud said.
Closing in on cancer Together with research centre Alphanov, in Talence, France, Amplitude is also developing a high power ultrafast laser that powers a secondary x-ray source. In this case they produce x-rays by accelerating electrons into a solid target. ‘The goal is to achieve a high brightness, high flux hard x-ray source dedicated to breast imaging,’ Courjaud explained. ‘The key optical considerations are peak power for conversion efficiency, and average power for the flux of the x-ray source. Since the source is inherently small, it naturally results in high brightness, which is the main interest of the laser-based x-ray source. Additionally, the x-ray source is naturally pulsed and ultrashort, which is of interest for moving objects or dynamic studies.’ After several years of work, the system produces x-ray images, Courjaud added, and is close to being used in breast screening tests. ‘We are now improving the characteristics of the X-ray source, through the conversion process and upgrading the laser source.’ Yet for direct use of ultrafast lasers in cancer surgery, Shephard agreed with Chui that fibre delivery is a key limitation. ‘Existing endoscopic surgical laser systems are restricted and cannot deliver
22 Electro Optics March 2021
such high peak power pulses with the flexibility required for precise, minimally invasive, procedures,’ he added. ‘With femtosecond laser surgery, the process speed is relatively slow and is impractical for appreciable tissue removal.’ Shephard’s team at Heriot-Watt is
therefore focussing on lower picosecond pulse rates, for which robust lasers are readily available today. They combine the precision and lack of thermal damage that femtosecond systems attain, but can remove tissue much faster.
delivery of the high peak power pulses, which enables tight focussing of the beam, in the order of 10µm, and hence giving a small focal volume within which the tissue ablation occurs,’ Shephard said. ‘The process is governed by non- linear absorption, so it is wavelength independent, which allows ablation of a wide range of tissues.’ Using a colorectal cancer tissue model,
the Heriot-Watt team has safely and accurately removed small polyps with surgical precision. ‘By adjusting the pulse energy and
rapidly scanning the laser across the tissue using a layer-by-layer, we were able to control the depth of removal approach to tens of micrometres per layer,’ Shephard said. ‘Histopathology confirmed the heat affected zone was minimised to below 50µm. This represents an order of magnitude improvement in precision. In the brain, for example, loss of even microscopic amounts of tissue can
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Spectra Physics’ Spirit One femtosecond laser is widely used in eye surgery
@electrooptics |
www.electrooptics.com
Dr. Varun Sharma
Spectra Physics
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