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Applications                         327

               I suppose that in the trade most people’s reaction was that sooner or later
            something useful was bound to come out of it. Radio waves have provided
            some service (even allowing for the fact that radio brought upon us the plague
            of pop music); microwaves have been useful (how else could you see the
            Olympic finals in some far away country from your armchair in Tunbridge
            Wells); so coherent light should be useful for something.
               The military who remembered that radar was useful also hoped that lasers
            would be good for something, and they gave their blessing (and their money
            too!).
               Another powerful contributing factor was the human urge to achieve new
            records. I could never understand why a man should be happier if he managed
            to run faster by one-tenth of a second than anyone else in the world. But that is
            how it is. If once a number is attached to some performance, there will be no
            shortage of men trying to reduce or increase that number (whatever the case
            may be). And so it is with coherent radiation. Man feels his duty to explore the
            electromagnetic spectrum and produce coherent waves of higher and higher
            frequencies.
               There may have been some other motives too, but there was no unbridled
            optimism concerning immediate applications. In 1970, ten years after the first
            lasers appeared on the laboratory bench (Theodore Maiman at Hughes Re-
            search Laboratories) we wrote in the first edition of this book: ‘None of the
            applications envisaged so far can justify the immense effort that has gone into
            the development of lasers but having developed them we may find that some of
            the possible applications are economical.’ That was 43 years ago. The number
            of applications now, in 2013, approaches the number of stars in the sky on a
            clear night. Let us mention a few. The military were right. They got a guid-
            ance system out of it which can direct a bomb dropped by an aeroplane into
            the middle of a plate of lentils, and there are, very likely, lots of other applica-
            tions in the pipeline. The ray-gun, that favourite dream of boys, science fiction
            writers, and generals may not be very far from realization. What about civil-
            ian applications? There are many of them in the medical field; there is optical
            radar, but of course the most important applications to date have been the com-
            pact disc and optical communications. There are many scientific applications
            too. We shall start with them.

            12.13.1  Nonlinear optics

            The whole subject, the study of nonlinear phenomena at optical frequencies,
            was practically born with the laser.

            12.13.2  Spectroscopy
            An old subject has been given a new lease of life by the invention of tun-
            able lasers. Spectroscopists have now both power and spectral purity previously
            unattainable.

            12.13.3  Photochemistry
            Carefully selected high-energy states may be excited in certain substances, and
            their chemical properties may be studied.
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