Laser Development

The first step is a careful assessment of what exactly is required. It is essential to realize all requirements at this stage, because it can be much more costly to introduce additional properties of the laser at a later stage.

As an example, one may consider a pulsed laser for an application where the precise pulse timing is critical. If that requirement is overlooked in the beginning, one may in the worst case choose a technological approach which makes it very hard to achieve the required timing accuracy. One may then be forced to either implement costly additional measures or to change the technological approach at a later stage.

The second step is to check whether the envisaged technology is overall appropriate, and perhaps to compare the chosen approach with competing options. This step is essential, because mistakes made at this stage would affect the whole development process. An experienced laser engineer is therefore strictly required.

As an example, there are many cases where a certain laser could either be realized as a bulk laser or as a fiber laser. Both technologies have specific advantages and limitations, the relevance of which strongly depends on the concrete case.

The next step is to work out a detailed laser design which can be used for building a prototype. This process involves quantitative checks of various issues before any laboratory work is started.

For example, if a passively mode-locked bulk laser is developed, this process can include calculations (not necessarily detailed modeling) concerning the pump intensity and laser gain (at different wavelengths), the threshold pump power, the balance of chromatic dispersion and nonlinearity in the resonator, the expected alignment sensitivity, the required modulation depth of the SESAM, the overall operation point of the SESAM concerning degree of saturation, the strength of pulse shaping, etc.

Such calculations go well beyond what could be done with a simple calculator; one will usually require a laser modeling software. With such a tool, various problems can be identified at the very early stage, then enforcing design changes until one obtains a design which is free of a number of foreseeable problems.

The “deliverable” of this design phase is a clearly written design report, containing not only all the parameters of the suggested prototype but also a clear description of the reasoning behind the design and possibly the likely limitations, some warnings, the list of required parts, etc.

Once the valve worked out prototype design exists, the required parts can be ordered and the prototype can be built, following the detailed prescriptions in the laser design. Obviously, it would be inefficient to start that phase without a proper prototype design, e.g. because one may then need to order additional components during the laboratory testing phase (causing additional cost and delays), and because various types of problems would be more difficult and costly to identify and solve.

The prototype may still exhibit some unforeseen problems – depending of course on the level of care and experience applied in the design phase. The design than his to be revised accordingly after identifying the origins of problems and suitable solutions for them.

Optimizing a design with further changes based on experimental tests in a trial & error procedure is often very time-consuming. For example, rearranging a laser setup often requires a complete realignment, and the same applies to rebuilding the original design if change turns out to be detrimental. Furthermore, the experimental results are often not conclusive or even misleading, since measured performance values can be affected by poorly controlled influences such as non-ideal alignment, dirty components or temperature changes. For such reasons, the effects of possible design changes can be much more efficiently and reliably evaluated with a suitable laser design software on a computer.

For various reasons, further steps often have to be taken to turn the prototype design into a final product design:

• Sometimes, the performance requirements change during the development phase, or additional requirements are discovered only then.
• One may discover that some tolerances (e.g. concerning misalignment) are still too strict for the final product.
• Generally, and industrial laser design must be subject to stricter requirements than a prototype, e.g. concerning aspects like efficient production, sufficient robustness for practical applications until harsh conditions, and overall convenient for the customers.
• One may want to minimize the production cost by working with fewer or cheaper components.

Again, one will have to evaluate the detailed effects of various design changes, which is often more time-consuming and less conclusive when done with experimental tests rather than using a laser model.

Other than the design document, the user manual can be written after all the prototype testing and refinement. Here, it is an advantage already to have all the practical experience with the device. It is important, however, that the author of a laser manual is able to fully recognize the needs of the end users, who have a less detailed knowledge of the technical details of the device. For laser engineer, this aspect can be somewhat challenging; it can then be very advantageous to have amenable checked by people who are not as closely familiar with the details.

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