FEATURE
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More power, more speed

Rob Coppinger discovers how new applications with fibre are keeping the laser industry in good health

Fibre lasers continue to make inroads into applications traditionally dominated by other systems and technical advances are making them more competitive. Whether it is nano, pico or femtosecond lasers, process improvement as well as technical advances are driving fibre lasers into new areas of use.

‘We have femto and picosecond lasers that are at the 10-20μJ pulse energy level. Our lasers can ablate without a build up of heat, marking transparent, sapphire substrates; it’s a really big market,’ says John Clowes, business development director at Fianium. Founded in 2003, Fianium specialises in ultrafast high power fibre laser systems. The company’s lasers are used in manufacturing, scientific and academic research, biomedical, industrial, scientific, imaging, tissue ablation and eye surgery.

‘It’s important not to damage parts of a structure and that is why ultrafast is really important for many applications,’ Clowes explains. Fianium’s lasers can provide a peak power of megawatts, delivered in one millionth of a millionth of a second. It is this high power in a short space of time that is the key advantage for Clowes.

‘Most company’s [traditional ultrafast systems] are based on diode-pumped solid state lasers. They are traditionally very large and quite expensive. The benefit of the fibre laser is its compactness and relatively low cost to manufacture in volume. It really allows a range of industrial applications to make use of ultrafast lasers for the first time.’

Clowes finds that when selling to academia the precise capabilities of the laser are not as important as they are for an industrial user. For the industrial customer they need to know that the system is the right one for their application. Fianium has invested in a laboratory with a number of its lasers. ‘We do customer-financed application trials to prove the principle so our lasers can be used for, for example, thin film ablation in photovoltaics manufacturing. That is how we market our lasers, doing applications trials.’

From 2009 to 2011 there was a drive by governments for investment in solar cells. A lot of capital expenditure in photovoltaic manufacturing was invested and associated with that. There was a big push for lasers for the manufacturing, scribing and dicing of photovoltaics. ‘But now it seems to have tailed off a bit,’ adds Clowes.

Fianium is finding that high brightness light emitting diodes is another application that is seeing greater interest, with a more sustainable market than photovoltaics. This is because high brightness LEDs are expected to replace traditional light bulbs in the next five to ten years. Femtosecond and picosecond pulsed lasers are able to scribe the sapphire substrates on which the LED devices are grown. ‘More recently the buzz is high brightness LEDs. That seems to be a more qualified industry than photovoltaics; it’s not heavily subsidised like photovoltaics was. There is a consumer market there that underpins this whole market for high brightness LEDs and the capital equipment needed to manufacture them,’ says Clowes.

Another key market for Fianium is scientific. The company will sell just one or two systems to customers in the research sector, whether it is corporate or university research. ‘Using the ultrafast fibre laser as a pump source we have been able to exploit nonlinear effects in optical fibres and we have developed a product called a super continuum fibre laser,’ explains Clowes. The super continuum laser is a white light laser providing a broad spectrum of wavelengths from visible to near infrared.

‘It is something that has been understood for 40 years. In 2005 we built the first high power ultrafast super continuum fibre laser. We have this turnkey product; we have sold several hundred of these units into academic research but also into corporate.’

Applications that have emerged for this type of laser include, high power lamp replacement, fluorescent lifetime measurement, spectroscopy, flow cytometry, fluorescent imaging and optical coherence tomography. Because the super continuum laser can provide all the wavelengths at once researchers only need to filter it and Clowes points to the fact that a single super continuum fibre laser can replace up to 10 discrete lasers and all of their associated drive electronics and beam combination optics.

Industrial and fibre laser manufacturer JK Lasers is tackling the important factor of the focus position of the laser relative to the work piece. Experienced operators will have their own methods for finding the focus of their laser, some better than others. JK Lasers has been developing a method that provides an accurate means of finding the fibre laser’s focus.

All of the company’s fibre lasers feature an integrated, patented technology that uses a fibre mounting scheme and angled capillary to protect against light that is reflected back from the workpiece. In addition, this back reflected signal is extracted internally to the fibre laser and the opto-electrical signal analysed. This can act as a system safety feature and a form of process monitoring. ‘We have found that by using carefully chosen parameters, this signal can be used to find the focus of the optical system,’ says Dr Stephen Keen, JK Lasers’ principal laser scientist.

A short pulse with sufficient energy to form a melt and fully couple into the material is chosen. At focus nearly all the light is absorbed by the material so there is a minimum back reflected signal. Away from this point the light intensity diminishes on the workpiece and more laser radiation is back reflected. This results in a larger signal at the detector.  By systematically changing the focus and plotting the signal it is possible to predict the focal position graphically.

The results of these early experiments were gathered using data acquisition techniques, but the company anticipates building the method into the control system. The company’s fibre lasers are controlled by a microprocessor-based system that is interfaced with a proprietary software suite called FiberView. This enables the end user to exploit the power of the control system. A focus wizard could be incorporated into FiberView to provide the end user with a reliable method of finding focus. This new technique, which is patent pending, is expected to enhance productivity and process knowledge transfer for end users.

While at IPG Photonics technical developments are leading to higher power and better polymer welding. ‘We have a Tulium fibre laser. We are starting to sell them for polymer welding. We have a 120W version available. It’s easily in excess of anything anyone else has in that range of 1.5-2μm,’ says Tony Hoult, general manager for IPG Photonics’ West Coast operations.

In Hoult’s view direct diode lasers suffer from low efficiency and low brightness. IPG has developed a 120W single mode fibre laser, which is used with a collimated beam. Developed for neurological applications, this 2μm, 1940nm, Tulium laser can generate a wide range of wavelengths. ‘And some are close to water absorption peak, so they have surgical uses, and German customers needed high power,’ says Hoult.

IPG’s researchers in Germany have been participating in the European Union Polybright programme. This is to develop lasers for polymer welding and an IPG laser used for the research is the ELM-500. ‘The ELM-500 is a prototype device. I have been using a production version and we are selling them for polymer joining, but most of the applications are covered in NDAs so we can’t talk about them,’ explains Hoult. ‘It has some advantages, you don’t need a specific colour and it’s all about joint design. You can weld clear polymer to clear polymer, if you get the joint design right.’

Publications from Polybright have been stating that laser operators should use a low F-number and steep tone angle at the interface between clear polymers for welding. However, in Holt’s opinion that is not necessary. ‘With the right laser, you can produce a butt weld. It’s all about having enough average power for a realistic speed and although polymers have low melting points you still need a large joint because polymers are so much weaker.’

It is because a large joint area is needed for polymers along with a lot of average power that IPG is bringing to the market this 120W laser. ‘We started to sell them over the last 12 months. It took me a while to get hold of one for the lab here. We showed it at a show earlier this year. There are a whole host of other applications. I really can’t go there,’ says Hoult.

IPG is finding new applications with its 2μm 120W laser but for now the company can’t disclose any of them. ‘Once you’re at that power level all sorts of things are possible. The whole physics changes; double the wavelength and things change fairly radically. There’s going to be any number of different applications,’ explains Hoult.

IPG has a research group at the University of Birmingham, Alabama. The Photon Innovation Group is looking at longer mid-IR wavelengths. ‘They are using crystal technology to go up to 3.5μm, mainly for scientific applications. It’s pretty interesting stuff,’ says Hoult.

In other developments Hoult explains that IPG is seeing interest in the use of nanosecond lasers for applications that have used picosecond systems. ‘We’ve taken picosecond applications that have got a picosecond laser at 10 times the price of a nanosecond one, and if you can show that you do it with a nanosecond laser at a tenth of the price, that’s a big commercial incentive.’