23.4 Lasers
659
(a)
(b)
(c)
(d)
Fig. 23.28 Images of the first semiconductor lasers, 1962: a GaAs laser, Lincoln Laboratories and b GaInP laser, N.
Holonyak and S.F. Bevacqua, Urbana Champaign. c Laser (at the end of gold bond wire) mounted on Peltier heat sink
and a TO chip, Universität Leipzig. d Size comparison of an ant with a laser chip (underneath the bond wire)
23.4 Lasers
23.4.1 Introduction
Semiconductor lasers
13 [1976, 1977] contain a zone (mostly called the active layer) that has gain if
sufficiently pumped and that overlaps with an optical wave. The wave bounces back and forth in an
optical cavity that leads to optical feedback. The part of the wave that exits the semiconductor forms
the laser beam. Some of the first semiconductor lasers and a mounting design are shown in Fig. 23.28.
Generally, two main geometrical laser types, edge emitters (Fig. 23.29a) and surface emitters
(Fig. 23.29b), are distinguished. The emission of the edge emitter exits through cleaved {110} side
facets
14 (≈ 30% reflectance), of which an opposite pair acts as a Fabry–Perot optical cavity. The surface emission is directed along (001), since this is the (standard) growth direction of the heterostructure
sequence making up the laser. The mirrors in a vertical-cavity surface-emitting laser (VCSEL) are made
from dielectric Bragg mirrors (cf. Sect. 19.1.4) with typically R > 99.6%. Using antireflection coating
13 The term ‘laser’ is an acronym for ‘light amplification by stimulated emission of radiation’. The amplification relies on
stimulated emission, theoretically predicted by Einstein in 1917. The laser concept was first explored in the microwave
wavelength region (1954, MASER using ammonia, Ch.H. Townes, Nobel prize 1964). The first optical laser (1958,
US patent No. 2,929,922 awarded 1960, A.L. Schawlow, Ch.H. Townes) was the ruby laser developed in 1960 by Th.
Maiman. A device is a laser when it emits stimulated light. This light must neither be monochromatic nor be emitted in
a narrow, directed beam.
14 Or etched facets in possibly any direction.
659
(a)
(b)
(c)
(d)
Fig. 23.28 Images of the first semiconductor lasers, 1962: a GaAs laser, Lincoln Laboratories and b GaInP laser, N.
Holonyak and S.F. Bevacqua, Urbana Champaign. c Laser (at the end of gold bond wire) mounted on Peltier heat sink
and a TO chip, Universität Leipzig. d Size comparison of an ant with a laser chip (underneath the bond wire)
23.4 Lasers
23.4.1 Introduction
Semiconductor lasers
13 [1976, 1977] contain a zone (mostly called the active layer) that has gain if
sufficiently pumped and that overlaps with an optical wave. The wave bounces back and forth in an
optical cavity that leads to optical feedback. The part of the wave that exits the semiconductor forms
the laser beam. Some of the first semiconductor lasers and a mounting design are shown in Fig. 23.28.
Generally, two main geometrical laser types, edge emitters (Fig. 23.29a) and surface emitters
(Fig. 23.29b), are distinguished. The emission of the edge emitter exits through cleaved {110} side
facets
14 (≈ 30% reflectance), of which an opposite pair acts as a Fabry–Perot optical cavity. The surface emission is directed along (001), since this is the (standard) growth direction of the heterostructure
sequence making up the laser. The mirrors in a vertical-cavity surface-emitting laser (VCSEL) are made
from dielectric Bragg mirrors (cf. Sect. 19.1.4) with typically R > 99.6%. Using antireflection coating
13 The term ‘laser’ is an acronym for ‘light amplification by stimulated emission of radiation’. The amplification relies on
stimulated emission, theoretically predicted by Einstein in 1917. The laser concept was first explored in the microwave
wavelength region (1954, MASER using ammonia, Ch.H. Townes, Nobel prize 1964). The first optical laser (1958,
US patent No. 2,929,922 awarded 1960, A.L. Schawlow, Ch.H. Townes) was the ruby laser developed in 1960 by Th.
Maiman. A device is a laser when it emits stimulated light. This light must neither be monochromatic nor be emitted in
a narrow, directed beam.
14 Or etched facets in possibly any direction.