A flexible approach to diode-pumped laser design combines customized performance with costeffective manufacturing.

Q-switched, diode-pumped solid-state lasers with an end-pumped cavity design are now widely used in micromachining, materials processing, marking, and related applications. They are used to process a broad range of materials including metals, glass, plastics, and semiconductors. But this application diversity creates a concomitant need for laser diversity. Namely, while each application requires superior reliability and performance, the definition of “superior performance” is very application-specific. For example, some metal ablation applications may benefit from a long laser pulse, whereas semiconductor scribing needs a short pulse and a very high pulse repetition rate.

Table 1. Relationship between pulsewidth and output power to other resonator parameters in aq-switched DPSS laser.

Figure 1. Soft Wafer Marking optimally requires a 1,064-nm Nd:YAG laser with a high pulse energy, a pulse length in the 200 ns range, and a repetition rate of around 1 kHz. This provides the necessary process throughput, since each mark consists of only a small number of individual holes. a) Characters produced on a silicon wafer using soft marking, and b) a close-up of the individual laser-produced bumps that make up the mark.

But there are many niche applications, as well as newly emerging applications, where the unit volume does not justify the engineering costs associated with designing a laser of this type. Coherent has answered this market need with the PRISMA family of diodepumped lasers, which utilize a flexible design approach. For example, every laser is built on an identical resonator baseplate that accommodates a number of different, predetermined optical configurations. This is accomplished by placing a series of precisely positioned holes, threads, and locating pins on the baseplate. Various sets of individual optical components are placed in standardized mounts and then attached to this baseplate as needed to produce the desired resonator configuration, and hence, the specific set of required output characteristics. This minimizes the fabrication cost of the laser and provides maximum design flexibility without requiring that each unit be manually aligned during production, eliminating unit-to-unit variation.

This flexibility also supports both Nd:YVO₄ laser crystals, which enable high pulse repetition rate (up to 150 kHz) and Nd:YAG crystals, which are optimum for high pulse energy at modest (<10 kHz) repetition rates. Furthermore, the cavity design enables the laser crystal to be end-pumped at one or both ends, providing flexibility in using significantly different levels of pump power. In addition, frequencydoubling crystals provide the option of 1,064-nm or 532-nm output.

As a result of this flexibility, PRISMA lasers have been optimized to successfully enable applications as diverse as soft wafer marking (see Figure 1), steel and ceramic mold form manufacturing (see Photonics Tech Briefs, April 2006, page 58), solar cell scribing, and ID card marking.

This article was written by Joerg Heller of Coherent Inc. For more information, contact Mr. Heller at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it , or visit http://info.hotims.com/10960-204.