Laser-based sensors

Some of the applications in this chapter overlap with others elsewhere in this book, particularly with Chapter 5 dealing with gas sensors and analysers, with Volume 2, Chapter 3 dealing with air pollution and with Volume 2, Chapter 7 on radiation pollution. However, the emphasis here will be on the different techniques rather than the applications. This book deals with sensors systems. The word sensor often conjures in the mind of the reader a very small device which is hopefully cheap to manufacture. On the contrary, in this chapter, we shall deal with laser-based sensors, which are often bulky and often very expensive. None the less, they are still validly called sensor systems and often have sensitivity and selectivity levels which cannot be equalled by any other techniques.