FEATURE
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Why diode lasers rule

John Ambroseo, CEO of Coherent, says high-power semiconductor lasers can help bring photonics back to growth

Following several years of strong industry-wide growth, the laser-based materials processing market fell off a cliff at the end of 2008 as sales dropped 30 per cent or more. In hindsight, we can clearly see how cheap and available credit fuelled both consumer demand and business investment, just as its absence led to a substantial contraction. Today, when asked about the materials processing demand cycle, the opinions of colleagues, customers and competitors range from ‘it’s not getting any worse’ to ‘things have stabilised’ to ‘we’re seeing a modest recovery’. While these represent varying degrees of moral victory, they say very little about the shape, dynamics or timeframe of a recovery. So we must ask ourselves what demand drivers will be in a post-Lehman Monday world.

In the most simplistic terms, a recovery is dependent upon an increase in consumer spending, government stimulus programmes or business investment. Consumers in many Western economies are de-leveraging following a multi-year period of debt-fuelled spending. Faced with high unemployment and home foreclosures, we cannot count on the consumer to lead a recovery in the near future. Government intervention may have prevented a global economic meltdown – but in many countries, the cost of bailouts, subsidies or incentives has limited any government-backed programmes designed to spur demand. Can business investment be the demand driver? The answer is ‘yes’ under one of two scenarios: first, we make existing markets more efficient, and/or second, we access new markets. Both are predicated on attacking the price-volume curve since photonics deployment in materials processing is limited, in large part, by its total cost of ownership (TCO, defined as acquisition costs plus operating expenses), especially when compared with traditional machine tools.

There are various philosophies for closing the TCO gap between laser-based solutions and machine tools. The most ubiquitous laser used in materials processing remains the venerable CO2 laser. Much work has been done to improve the reliability of CO2 lasers and reduce their service costs. This has resulted in broader adoption in diverse applications from package marking to metal cutting, while simultaneously lowering their TCO. Nonetheless, the low power market for CO2 lasers is a game of cost and reliability. By contrast, increasing the power output of CO2 lasers, especially in the multi-kW regime, has led to several desired outcomes: Tool throughput (i.e., parts per hour) has increased; the cost (dollars-euros-yen) per Watt ratio has dropped; and perhaps most importantly, a process window for cutting metals in the 4-6kW range has proved resistant to fibre laser intrusion based upon the previous factors, plus the superior quality of the finished product.

Applications served by near infrared (~1μm) lasers have undergone a tremendous share redistribution based on the benefits of fibre lasers. Legacy products such as lamp-pumped or diode-pumped solid-state lasers have difficulty competing with the efficiency, reliability and ease-of-integration of fibre lasers, particularly in the 1-2 kW regime – arguably the sweet spot for fibre lasers. Yet, despite their obvious benefits, fibre lasers have not, in any meaningful way, expanded the overall market for lasers. The reason for this is the fibre laser’s TCO. The problem is not that it is unreasonably high, but rather that it is not low enough to aggressively enable new markets, such as welding.

The one technology poised to break the TCO barrier is high power semiconductor lasers. There are several reasons for this. First and foremost, diode lasers can be mass produced and packaged using automated assembly, which drives reliability, lifetime and unit-to-unit consistency. They’re compact and more electrically efficient than fibre lasers, even when fibre-delivered. There has been tremendous progress on power scaling of individual emitters, bars and arrays. Combined, these factors reinforce the cost advantage up and down the power scale compared to other technologies. When you add microlensing and fast modulation capabilities, the diode laser stands out as a truly enabling light source. The one parameter currently holding diode technology back is brightness. However, with new semiconductor architectures being developed around the world, the brightness barrier will also be overcome. When that happens, it’s not difficult to envision diode laser system prices approaching $40 or less per Watt, thereby creating a wave of adoption well beyond today’s material processing market boundaries.