Masers and Lasers, 2nd Edition

163

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

164

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 resonant cavity

and so space was saved. He then decided

that instead of putting the double dewar

inside the monster magnet, he could

put a small permanent magnet inside

the dewar. It was thought that the mag-

net would crack and break although it

Pump

Dewar

MagnetMagnet

Maser material

Resonant

cavity

Signal

FIGURE 6.1 A typical set-up of a

traditional solid-state maser.