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6
The First Lasers
6.1 Introduction
Immediately aer the publication of the paper by Schawlow and Townes (see
Chapter 5), a number of researchers started to think about dierent systems
for the production of inverted populations in the infrared and visible regions.
We shall see in the following sections that many dierent approaches were
considered almost simultaneously and independently and that, in the case
of semiconductors, considerations of the possibility of producing radiation
through stimulated pair recombination even preceded the Schawlow and
Townes discussion.
Of course the main lines were inuenced by the ideas of these two
researches and most people were expecting the rst laser action to take place in
an excited gas. However, not everybody was working on gases. It so happened
that the rst working laser was realized in May 1960 at the Hughes Research
Laboratories by eodore Maiman, using ruby as the active material.
1
6.2 The Ruby Laser
e rst laser was realized in May 1960 at the Hughes Research Laboratories,
Malibù (Southern California) by eodore H Maiman, using ruby as the
active material.
eodore H Maiman (1927–2007) was the young head of the quantum
electronics division at Hughes. Aer supporting himself in college by repair-
ing radios and other electrical appliances—an inclination he inherited by his
father Abe, an electrical engineer—and then serving in the Navy, Maiman
earned a BSc in engineering physics from Colorado University, an MSc in
electrical engineering, and a PhD (1955) in physics from Stanford University,
where his doctoral research
2
was in microwave spectroscopy under Professor
Willis Lamb. en he became a research scientist at Lockheed Aircra for
Masers and Lasers
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a short while, studying communication problems connected with guided
missiles.
Later he accepted a position at Hughes Research Laboratories (HRL) in
Culver City, California. At Hughes, he went to work in the newly formed
Atomic Physics Department, where the principal interest was to generate
higher coherent frequencies than were currently available. is was about
the time that the ammonia maser came about. Hughes had an intense inter-
est in maser research at that time. At rst, however, Maiman worked on a
dierent contract. When he nished this work, he had wanted to work in a
fundamental research capacity, but the Army Signal Corps, which sponsored
the research, required at that time a practical X-band (i.e., at a wavelength
of 3 cm) maser. ey did not want any state-of-the-art advances, but simply
wanted that maser, and Maiman was asked to head the project. He was not
very enthusiastic at rst because the project involved a practical device and
he was more research-oriented. But then he became more interested and even
though they had not demanded any tremendous advances, he decided he
could certainly make the maser more practical.
Masers at that time had two serious practical drawbacks. e main di-
culty was that a solid-state maser, which is a more useful type, needs to work
at very low temperatures. Indeed, liquid helium temperature was needed, that
is, only 4 K. e other problem was that the conventional maser used a huge
magnet, weighting about 2 tons, to obtain the Zeeman levels needed for the
maser action. Inside this magnet was a dewar in which had to be poured liquid
nitrogen in order to start lowering the temperature. Inside this dewar, another
one was placed which was full of liquid helium. e real maser was a small
microwave cavity, with the crystal in its interior, which was positioned in the
liquid helium dewar between the pole faces of the magnet (see Figure 6.1). e
magnet had to create a strong magnetic
eld within the whole volume occupied
by the two dewars and the maser cavity,
which justied its great size. e pre-
ferred maser material at that time was
ruby. Maiman decided that there were
a certain things he might be able to do
still using ruby. He made a miniature
cavity from ruby by cutting it into the
shape of a small parallelepiped. en he
painted a highly conductive silver paint
over the ruby and put a small hole in it.
In this way, the ruby behaved as both the
active material and the res