FEATURE ULTRAFAST LASERS
Boosting ultrafast lasers’medical benefits
Picosecond and femtosecond lasers are moving beyond ophthalmology into applications including cancer screening and therapy, finds Andy Extance
I
n the battle to give people the longest, healthiest lives possible, cancer is one of our oldest foes, with some Egyptian mummies showing signs
of bone cancer. The US government even declared war on cancer in 1971, and called for a ‘moonshot’ to end cancer as we know it in 2006. The resulting intensive medical effort has made many cancers treatable today. Yet modern populations are getting older on average, and older people’s cells are exposed to more factors that can make them mutate and become cancerous. As such, there are still significant benefits to gain from more successful cancer treatment, according to Jonathan Shephard, from Heriot-Watt University in Edinburgh. His team is working on developing ultrafast lasers for cancer surgery, removing cancerous tissue with higher precision than conventional lasers, and without damaging surrounding tissue. ‘In the duration of the pulse, a few picoseconds, there isn’t sufficient time for heat to diffuse to the surrounding regions, as is the case for longer pulsed nanosecond or continuous wave lasers,’ Shephard said. Today, ultrafast lasers are already
routinely used in eye surgery. Yet there are challenges in deploying them elsewhere in medicine, which means they are not widespread. Researchers like Shephard are looking at
ways to overcome the technical obstacles to gaining their benefit. In cancer treatment, the advantages include reduced need for rehabilitation and supportive services, making it easier for patients to return to normal lives. ‘The improvement in the precision at which cancers can be removed will reduce the risk of complications,’ Shephard said. It would also remove cancers more
20 Electro Optics March 2021
completely, reducing recurrence rates and the resulting personal and financial costs. One supplier of ultrafast femtosecond pulse duration lasers for ophthalmic surgery applications is Spectra- Physics, a brand of MKS Instruments, headquartered in Massachusetts. Herman Chui, MKS senior director of marketing, highlighted the general benefit of laser- based procedures compared to surgery using a scalpel: ‘If you get a better patient outcome, that can save you from healthcare costs.’ The other main medical application for
Spectra-Physics’ ultrafast lasers is making implantable devices such as stents and catheters. ‘If you’re putting something in the body, you need the highest-quality surfaces on these devices,’ Chui explained. ‘By using ultrashort pulse lasers, you can achieve that. ‘You’re not necessarily limited in power
or energy, and you may look at different wavelengths. For example, some of the biodegradable materials react better with green wavelengths versus infrared wavelengths. There is less thermal impact, shallower absorption depth, and you can get a better cut quality in those materials without melting.’ Spectra-Physics supplies lasers to
ophthalmic surgery instrument producers. ‘We have many thousands of lasers deployed for this application,’ Chui said. That includes doing research to improve femtosecond lasers for eye surgery applications, taking great time and care to develop customer-specific products. Design changes tend to bring major advances, because medical instruments require approval from regulators such as the US Food and Drug Administration. Only major changes make it worth going through this process.
Finding the right target Improvements typically involve parameters other than power, Chui explained. ‘The eye can only take so much power,’ he said. ‘It’s not like if you had more power, you could do more surgeries. It’s different than manufacturing, where if you have more power, you can manufacture more smartphones. Short pulse length is important but some of it is reliability, cost of ownership, size. It’s got to go into a doctor’s office, so it’s got to work all the time.’ Penetration of ultrafast lasers into
ophthalmic surgery comes because the pupil is transparent, allowing access to the inside of the eye with light. However the tissues being operated on are also delicate, Chui stressed. ‘In a lot of other applications it’s okay to use a cruder laser
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