Heriot-Watt University
Amplitude
FEATURE ULTRAFAST LASERS
“The extent of thermal injury to a tissue is proportional to the magnitude and duration of the temperature increase that it experiences”
Ghosh continued. ‘We can also tune the laser across the wavelength range from 570 to 596nm. We have also observed excellent power stability over a long duration, opening up the possibility of having a handy source for various applications.’ The ultrashort pulse length and
Amplitude Laser supplies ophthalmic surgery instrument producers g
seriously affect function and quality of life.’
Shephard is ‘confident that we can use
this process in many areas where the disease infiltrates vital organs.’
New colours shine through Meanwhile, Goutam Samanta’s research group at the Physical Research Laboratory in Ahmedabad, India, is addressing other medical applications by extending the wavelengths available to femtosecond lasers. Long pulse tunable dye lasers can be used in dermatology to remove port-wine stain (PWS) birthmarks, explained team member Anirban Ghosh. However, whereas existing instruments can damage the skin being treated, yellow femtosecond lasers should have optimal properties for this application. ‘Even 60 years since the first
demonstration of lasers, we only have a handful of commercially available lasers with selective wavelength coverage across the electromagnetic spectrum,’ said Ghosh. ‘This is mainly due to the unavailability of suitable laser gain media.’
Commercial yellow lasers do not
exist, even though bulky and inefficient copper vapour lasers and dye lasers and optical parametric oscillators have been used successfully. Each of these suffers drawbacks of low average power, lack of adequate spatial beam profile, limited or no wavelength tunability, and broad output pulses. By contrast, the Physical Research
Laboratory has demonstrated a ‘relatively easy and straightforward system architecture to generate high power, high repetition rate ultrafast tuneable solid-state laser systems in the yellow wavelength range’, Ghosh said. ‘We developed a compact source of high power, tunable, ultrafast yellow radiation using the single-pass fourth- harmonic generation of a mid-IR laser in two-stage frequency-doubling processes. ‘We have frequency-doubled the
By adjusting the pulse energy and rapidly scanning the laser across the tissue using a layer-by-layer, the Heriot Watt University team was able to control the depth of removal approach to tens of micrometres per layer
24 Electro Optics March 2021
ultrafast mid-IR laser at a central wavelength of 2,360nm in two different nonlinear crystals and used simple optical components available in any standard optics laboratory to achieve high power, tunable, ultrafast yellow laser source. ‘The laser could provide us a maximum output average power over 1W with 130fs pulses at a repetition rate of 80MHz, with an outstanding spatial beam profile,’
the yellow colour are the two main parameters for medical applications, Ghosh added, but beam profile is also important. ‘Focusing the laser beams to the
diffraction limit to reduce the collateral damage of the tissues requires the source to have a good spatial beam quality,’ he said. ‘For example, in the case of the
therapeutic effects of macular photocoagulation, the extent of thermal injury to a tissue is proportional to the magnitude and duration of the temperature increase that it experiences. Temperature rise at the periphery of a photocoagulation lesion may be lower than that at its centre, because of heat conduction or lack of a uniform beam profile. Thus, it is good to use an ultrafast pulse laser with an excellent beam profile, in such applications.’ To realise the benefits of such
advances will likely take the involvement of companies like Amplitude, which specialises in making the switch from research to industrialisation, explained Guillot. ‘If we look at the X-pulse project, in
theory, we know how to do it,’ he said. ‘What we’re unable to do today is to
produce 100 machines that could be used on a daily basis. If we want to have a medical application, we need to be able to produce something industrially, otherwise it remains a very niche market.’ Guillot is optimistic that the systems ultimately in development will make that transition. ‘Let us hope that tomorrow these
ultrafast lasers will also contribute to the benefit of humankind,’ he said. EO
@electrooptics |
www.electrooptics.com
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