“We now offer precise solutions rather than pure hardware”

Coherent develops and produces optically pumped semiconductor lasers and diode-pumped solid-state lasers at its plant in Lübeck, Germany. Managing Director Dr. Reinhard Luger focuses on the target markets microelectronics/semiconductors, biophotonics, and additive manufacturing. In the interview, he talks about technological challenges in these markets, the importance of platforms and modular construction, and the drivers of Coherent's recent outstanding growth.

Dr. Luger, what role does the Lübeck location play for Coherent?

Dr. Reinhard Luger: Our roots go back to the 1980s. Back then, our founding team in the former ADLAS GmbH began developing and producing diode-pumped solid-state lasers, including frequency doubled green lasers. It was a pioneering technology at that time. Coherent noticed this and acquired the company in 1995. These days, we mainly develop and produce optically-pumped semiconductor lasers (OPSL) and diode-pumped solid-state lasers (DPSS). We are one of the largest business units in the Coherent Group—and a flagship location with regard to lean management. We develop our products and the means of production simultaneously and focus on system flexibility so that we can quickly produce high numbers of units and achieve optimum capacity utilization.

What are your most important target markets?

Luger: We operate in three main segments: microelectronics/ semiconductor, life sciences/biophotonics, and additive manufacturing. The semiconductor segment uses our lasers primarily to inspect structured and unstructured wafers. Our UV lasers offer a high degree of reliability and as a result, are especially in demand here. With our current systems, a service interval is more than 20,000 hours of operation. In addition to inspection applications, our lasers are also used in the semiconductor industry for ablation, cutting, and thin-film exposure within the scope of PCB production. The PCBs are lithographically coated and exposed with a UV laser before the traces are applied using an etching process. Large, multi-layer PCBs in particular can be manufactured inexpensively with this process. Marking is another important application in microelectronics, which we support with Q-switched lasers. Our second largest market segment is bioinstrumentation, where lasers are primarily used for fluorescence excitation in devices for medical diagnostics, as well as in microscopy. Small lasers that emit as little heat as possible and that have a high beam quality and offer a large selection of wavelengths are required in this area. The third area is additive manufacturing where our Q-switched lasers are used with photopolymers (i.e., epoxy).

What are the differences between OPSL and DPSS technology and what are the respective strengths?

Luger: The main difference is that diode-pumped solid-state lasers (DPSS) pump (excite) a solid-state crystal that is doped with rare earths. On the other hand, the optically-pumped semiconductor laser (OPSL) uses a diode laser to pump a ternary quantum well structure of indium gallium arsenide (InGaAs). The latter is very thin, enabling efficient cooling, with miniscule heat load. As a result, hardly any thermal lensing occurs, even at high pump powers. This means that both the power spectrum and beam quality are not affected by changing the laser power. Another strength of the OPSL is that its quantum well structure enables light to be generated across a wide infrared spectrum and be converted into visible light, from blue to orange, via efficient frequency doubling. Consequently, it is relatively easy to design lasers for specific wavelengths over a large wavelength range. This opens up completely new possibilities in spectroscopy and fluorescence microscopy. Additionally, these applications really benefit from the OPSL’s ability to be adjusted down to only one percent of their rated output power without them becoming unstable. In contrast, crystal lasers are best operated only within their 90-100% power range.

You mentioned additive manufacturing. What challenges does this pose for lasers?

Luger: As I said, we are active in the plastics segment, or to be more precise, in processes where UV lasers cure epoxy resins. In addition to the usual requirements, such as service life, reliability, and integration in small packages, two things are important. First, the beam must be round across a large focal range. Beam astigmatism and elliptical distortion have a negative impact on the precision of the created component. Second, there is a requirement for high power stability in fast switching operation. While the component is being exposed, the laser is continuously switched on and off and its full power must be available instantaneously at the next pulse. There is no time for adjustment in the additive process because every power fluctuation has an immediate and permanent effect on the quality of the component.

Biosciences and microelectronics are entering new realms. Both need precise but also flexible light sources. How can this be achieved despite the high cost pressure?

Luger: It’s true, we are experiencing rapid progress with flow cytometry, confocal microscopy, and DNA sequencing. For these applications, there is demand for an increasing range of wavelengths and for systems that integrate optics, mechanical components, and several lasers, especially for multi-parameter analyses. In the semiconductor area, the feature dimensions are also almost inconceivable. In wafer inspection for example, the challenge in defect detection is similar to finding a golf ball in the Sahara within 20 seconds – with 99.8 percent accuracy and even higher fault precision. In each case, challenges flow up-stream to our laser systems. Our solution is to ensure the highest level of precision and flexibility within an economically acceptable framework, and similar platforms. The parallel development of product and production methods allows us to implement many different products of the same type and to produce them inexpensively on one single manufacturing platform. This includes using as many of the same parts as possible, process automation, and a highly developed quality management system. The demands for increasing precision are pushing us towards the limits of testing metrology. In the area of UV lasers for example, there are no straightforward means of measurement that are accurate enough to measure and prove the required beam quality. We are on the lookout for solutions, but many times, we engineer our own.

Users in the life sciences are often not laser experts. How do they keep track of the increasing variety of light sources and photonic processes?

Luger: This certainly is a challenge. We have to offer customers applications-specific support, advise them before they purchase laser systems, and show device manufacturers just what our different lasers are capable of. Our engineers often go directly into the development and service departments of our customers and support them through to the layout of the optical design. We now offer precise solutions rather than pure hardware for the specific problems that our customers address.

One last question: Coherent recently reported enormous growth. Apart from the Rofin takeover, what are the most important drivers?

Luger: Obviously, there is a step-function increase due to the acquisition, which provided the company with additional strength in high-power fiber lasers as well as complete laser material processing systems. But other businesses have been growing as well. For example, our LineBeam annealing systems, which are in demand for the production of polysilicon (LTPS) display panels. This business has been paced by the continuing growth of mobile devices globally. A combination of organic growth and acquisitions continues to expand our technology and product portfolio. The acquisition of Lumera Laser in 2012 is a good example of the latter. Their unique expertise in the area of ultra-fast solid-state lasers has proved to be a wonderful supplement for us. Coherent has the global infrastructure and the necessary business knowledge to leverage innovative technologies like this into worldwide market success within a short time.

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