fibre is even removed from the body. Certain medical interlock systems

are automatic and have proven to be unpopular in the past, as they have the ability to disable a laser without a doctor’s permission during a delicate procedure – for example if an unauthorised person enters the operating room. Lasermet have addressed this problem through designing a maglock-based interlock system that avoids unwanted interruptions to a laser by preventing the doors of an operating room being opened whenever the laser is activated. In doing this, the safety of the doctors and patients is ensured while the integrity of the operation is maintained. Authorised personnel are still able to enter the room by using a keypad override system that deactivates the maglock without interrupting the laser.

Harmful optics Much of the training and precautions in laser usage are shared between industry and medicine, according to Bailey. One difference between the two is medical users must be made aware of certain hazards associated with the optics used within medical lasers: ‘We’re now seeing more applications using holmium and erbium lasers for various medical procedures… they are quite far into the infrared and can use optics that are potentially quite dangerous if they go wrong.’ Bailey pointed out that lenses within

lasers can degrade and become damaged over time: ‘For example, if some dirt got on a lens… the dirt could burn and cause

Medical applications can use a range of wavelengths that the patient has to be protected against

damage to the lens itself. Once that starts happening the lens can … eventually break and shatter in the machine.’ When zinc selenide lenses start

to degrade, toxic gases and dusts of hydrogen selenide, selenium dioxide and selenium are released into the surrounding atmosphere, according to Bailey. This can apparently be seen as an emission of red or white smoke and can be smelt as a garlic-like odour. ‘Anyone smelling the initial smell needs to immediately stop and put on facial protection to stop them from breathing in the fumes,’ stated Bailey. ‘It’s really about having an awareness of knowing when there is a problem and how to address the problem before continuing with a medical procedure. ‘These lenses need to be taken away and carefully disposed of. Being aware of this is

part of the safety issue and something that medical laser users have to be taught.’ Pro-Lite Technology runs frequent laser

training courses; the next one is 14-15 March in Cranfield, UK.

Toxic plumes The medical practical applications seminar (MPAS) is one of the three presentation tracks of the International Laser Safety Conference (ILSC) taking place in Atlanta, USA on 20-23 March. The four-day event will cover all manner of laser safety practices, hazard-controlling methods and the latest research regarding laser safety. The conference will also play host to multiple discussions on the everyday scenarios encountered by laser safety officers (LSOs). One of the medical seminars, ‘Laser

Extreme laser safety

Research centres like the Extreme Light Infrastructure (ELI) and the European XFEL being built in Hamburg, Germany, contain some of the most powerful lasers in the world, all for probing fundamental physics. Ensuring safety at these sites presents its own unique set of challenges, something that laser safety specialist Lasermet is currently working on for the European XFEL facility. Lasermet is installing an

interlock safety system for the XFEL centre. ‘In these projects, there are multiple rooms with multiple sources delivered to multiple target areas – the laser light could go to any one of those areas,’ explained Paul Tozer, managing director of Lasermet. ‘From a safety interlocking point of view, it’s a bit of a nightmare. It’s a big departure from the

32 Electro Optics March 2017

normal laser safety interlock situation, where there is a laser contained in a laboratory.’ Lasermet has done work in the

past for the UK Atomic Weapons Establishment (AWE) where there were a number of target chambers to which the laser could be delivered. ‘With these more complicated

setups, you get to a situation where you have to solve it with logic,’ Tozer said. Lasermet built its Safety Logic Plus interlock system for AWE because the organisation wouldn’t accept a software-based device. Safety Logic Plus uses DIN

rail mount logic gates, which are hardware based. The user develops a logic diagram for a safety system; there is then a physical logic gate on the DIN rail for each logic gate in the safety

plan. The product conforms to the safety integrity level SIL3, and to the safety control system standard EN13849-1 at performance level E, as do all the company’s laser interlock systems. ‘The other thing that makes the design of safety systems for the ELI and European XFEL projects a safety interlocking nightmare is that you’ve got secondary radiation produced by these systems,’ said Tozer. ‘Instead of the laser radiation being a danger of serious injury, there is a danger of death. Essentially, you’re walking into a room, the laser source isn’t in that room, but if the laser source is connected to it there is danger of death. You have to have a means of detecting in a foolproof way whether the beam is going into that room, and not allow the beam to go into there

until you’ve gone through a series of safety procedures.’ In the ELI project, the beam is

delivered through vacuum tubes with gates and mirrors. Each of those has an interlock switch, so the safety system detects where the beam is being directed from the position of the mirrors. ‘You have to define the

circumstances under which the laser is allowed to fire,’ Tozer said. ‘Because of the dangers involved you need to build up [the logic diagram] very carefully. You don’t want it to be flexible; the point is you mustn’t change it. ‘Once you get multiple rooms

– say six rooms – where you could produce the laser radiation and another six experimental halls where you could deliver it, the logic is quite complex,’ he concluded.

@electrooptics |

Laser Components

Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44