FEATURE
Issue: 

Efficiency gains

With direct diode lasers making their way into industrial settings alongside fibre and CO2 lasers, Jessica Rowbury looks at how important energy efficiency is for end users choosing a laser system

Increases in average power and improvements in beam quality mean that highly efficient direct diode laser systems are starting to make their way into metal cutting applications. This was demonstrated at this year’s Photonics West, where a number of direct diode systems were on display marketed as replacements for CO2 lasers. So, how does energy efficiency affect users’ decisions when purchasing a laser system, and are other factors such as performance more important?

With energy consumption having a large impact on cost of ownership, the efficiency of a laser system is a key consideration for end users choosing a laser system. ‘It is an important point in [a user’s] decision for laser choice because the investment cost of all lasers is quite high, so people are trying to use lasers on a 24/7 production scheme. This means that the energy efficiency is directly related to the overall cost of the lasers,’ explained Andre Eltze, sales manager for Europe at Laserline.

And, for producers of laser systems, improving energy efficiency is significant for not only reducing operation costs of their customers. It also allows for a more cost efficient design of the laser itself. ‘To manufacturers, the overall efficiency is more important due to the dimensioning of laser cooling, power supply and cabling. This has an effect on manufacturing costs,’ commented Dr Markus Röhner, head of product management at Jenoptik.

Direct diodes

With efficiencies approaching 50 per cent, direct diode lasers are surpassing the energy performance of CO₂, and to a certain extent, fibre and disk lasers. ‘The most efficient laser systems on the market are diode lasers, where you use the light from the diode directly,’ stated Eltze. ‘Its direct conversion from electricity into light, just like LEDs are the most efficient light sources for household applications, for example.’

As direct diodes have increased in average power and improved in beam quality, their uses have expanded from surface and brazing applications to industrial welding. ‘They are pretty widely used − for cladding, welding, hardening, soldering − and that goes from very small parts, such as welding cameras in mobile phones, up to welding car bodies,’ Joerg Neukum, director of sales and marketing at Dilas, remarked. 

Now, high brightness diode systems are being released positioned for metal cutting. In the past, the beam quality of direct diode lasers was not considered good enough for this application. 

At this year’s Photonics West in February in San Francisco, a number of direct diode laser systems were displayed highlighting how these lasers are slowing entering the market for metal cutting. 

Laser provider, JDSU, exhibited turnkey 2kW and 4kW direct diode laser systems at the show, which the company is positioning as a replacement for the less efficient CO₂ laser in thick sheet metal cutting, welding and surface treatment. These systems are targeted at cutting thicker metals, where fibre lasers would be less suitable.

Laserline also launched its LDF 4kW diode laser with beam converter, which opens up new applications for diode laser technology such as remote welding and laser cutting.

Compared to direct diode systems, CO₂ lasers have a high cost of ownership and low electrical to optical conversion efficiency. ‘If you compare direct diodes for cutting applications, we expect them to get up to 45 per cent efficiency. A CO₂ laser, to my knowledge, is somewhere in the range of 10 to 12 per cent efficiency. But direct diode and fibre lasers are in the range of 40 per cent, so they are the most efficient lasers,’ said Neukum. 

As the efficiency of direct diode starts to exceed fibre lasers, the technology is very attractive for certain material processing applications: ‘If you want to produce a 1kW fibre laser, you need 1.5kW of diode light to pump it. And, if you want to produce 1kW direct beam diode or direct diode light for cutting, you may need 1.2kW of diode light because you will also have some fibre coupling losses,’ Neukum explained. ‘So, you might be a bit more efficient and you’re not stuck to one wavelength, so you can combine several wavelengths, which for some applications is advantageous.’

Professor Reinhart Poprawe, director of the Fraunhofer Institute for Laser Technology ILT, commented in an interview for Electro Optics: ‘Diode lasers replacing older, less efficient technology for cutting would have a huge impact; it’s a billion dollar market served almost solely by CO₂ lasers because of the advantages of the wavelength and convenience of the systems. But the efficiency of CO₂ systems is pretty poor, so this would be a fantastic jump if you have the right wavelengths and beam quality in diode lasers. This isn’t the case currently, but it would be a long-term relevant goal for laser technology for the future.’

Performance vs. efficiency 

However, while energy efficiency is important, the primary consideration for end users when choosing a laser system is its performance, according to Andre Eltze, sales manager for Europe at Laserline. ‘The performance is certainly the first thing people look at for a specific application. If a laser is not suitable for a certain task, then people don’t care about energy efficiency − it’s useless.

‘Appropriate, adapted beam quality and adapted output power are the most important for the decision in choosing a laser system,’ added Eltze. ‘The energy efficiency and costs are in the second step.’

And while the efficiencies of CO₂ lasers remain considerably lower than diode and fibre lasers, their versatility means they will always be the best laser for certain applications, no matter how efficient they become. ‘I think CO₂ will always have its market because the CO₂ is such a long wavelength that it is essentially absorbed by so many materials,’ Neukum remarked. ‘If you’re in a job shop and you have to cut different materials all of the time, from metal to cardboard to plastics, you might want to go with a CO₂ laser.

‘For example, with CO₂, you could do cutting of transparent plastic or cutting of glass, whereas glass is transparent for most fibre lasers and most diode lasers,’ Neukum continued. ‘So, the CO₂ will always have its market.’

It can also depend on the global region as to how important energy efficiency is, as well as how fast the more efficient systems will be adopted. ‘In some countries where energy is expensive and where space is expensive, for example in Japan, you might have chances to introduce compact direct diode lasers for cutting much faster in countries where space is not expensive and energy is not expensive, for example North America,’ Neukum continued. ‘So, there will be regions where energy efficiency is a key part.’

Although it can be argued as to whether efficiency is the most important factor for end users choosing a laser system, improving energy performance remains a major priority for manufacturers of laser systems. ‘[Improving efficiency] is one of our goals. We’ve recently shown that with diode lasers − the complete system including the power supply, control system and other components − we can achieve 48 per cent wall-plug efficiency, and we’re trying to surpass the 50 per cent limit with the overall efficiency of the laser system,’ Eltze commented.

‘We’re working on efficiency of the diodes, of the power supply, of the control system, the optical efficiency inside the lasers. There are many points to average at the same time, so we’re working on all of these,’ Eltze continued. 

According to Jenoptik’s Röhner, efficiency will become more of an important deciding factor in the future, although advances will be slower than they have been over the last few years. ‘Non-regenerative energy resources are limited. That’s why the energy efficiency becomes more and more important in the future. This will also affect the development of the laser systems,’ he commented. ‘Manufacturers will improve their technologies in order to increase the efficiency of their laser systems. But progress will be slower than in the past due to the fact that lasers are already exceeding 50 per cent efficiency (or are at least coming close to 50 per cent).’

But other than energy performance, further improvements in beam quality and power will mean that the more efficient systems such as direct diode will move into a wider range of application areas, according to Eltze: ‘The driving factor I believe is not the efficiency; it’s the capability, certain power and beam quality. [Diodes] are moving into new and very exciting applications.’ 

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