23.4 Lasers
661
Fig. 23.31 Evolution of optical data storage technology, ‘CD’: compact disk (laser: 780 nm, pitch: 1.6 µm, capacity:
0.7 GB), ‘DVD’: digital versatile disk (laser: 635–650 nm, pitch: 0.74 µm, capacity: 4.7 GB for one layer), ‘BD’: ‘Blu-ray’
disk (laser: 405 nm, pitch: 0.32 µm, capacity: 27 GB for one layer)
• optical information storage and retrieval (CD, DVD, BD
16 ) with as short of a wavelength as possible,
as shown in Fig. 23.31, currently 405 nm.
• pumping of solid-state lasers, typically 910 or 940 nm for pumping Nd:YAG
• portable projectors, laser TV, entertainment.
• laser pointers, see Fig. 23.32. A red laser pointer simply uses the collimated red emission of a GaAsbased diode. In a green laser pointer, an infrared diode pumps a Nd:YAG or Nd:YVO 4 crystal. The
emitted beam is then frequency doubled, typically with a KTiOPO 4 (KTP) crystal.
• medical instruments with a variety of wavelengths in ophthalmology, dermatology, cosmetics (hair
removal, tattoo removal).
• various other uses, such as remote control, position detection, distance measurement, printing, scientific instrumentation.
The market for photonic devices is much more dynamic than the electronics market. An example is the
rapid change of dominating laser applications. For diode lasers, the two most prominent applications
are telecommunication (77% market share in 2000, 25% in 2003, 45% in 2008) and optical data storage
(17% market share in 2000, 60% in 2003, 44% in 2008).
23.4.3 Gain
Due to current injection,
17 a nonequilibrium carrier distribution is created. After fast thermalization
processes (phonon scattering), it can mostly described by quasi-Fermi levels. Sufficiently strong pumping leads to inversion, i.e. conduction-band states are more strongly populated with electrons than
valence-band states (Fig. 23.33). In this case, the stimulated emission rate is stronger than the absorption rate (cf. Sect. 10.2.6). The thermodynamic laser condition (cf. (10.23)) requires the difference of
16 16 million 405 nm laser diodes were shipped in 2006–2008. 85% of those are built into SONY’s PS3, the rest into
HD-DVD and other Blu-ray™disc (BD) players.
17 or due to optical pumping. If electrical contacts are not available, the laser action can be invoked by supplying a
high-intensity light beam, possibly in a stripe-like shape. For optically pumped semiconductor lasers see Sect. 23.4.15.
661
Fig. 23.31 Evolution of optical data storage technology, ‘CD’: compact disk (laser: 780 nm, pitch: 1.6 µm, capacity:
0.7 GB), ‘DVD’: digital versatile disk (laser: 635–650 nm, pitch: 0.74 µm, capacity: 4.7 GB for one layer), ‘BD’: ‘Blu-ray’
disk (laser: 405 nm, pitch: 0.32 µm, capacity: 27 GB for one layer)
• optical information storage and retrieval (CD, DVD, BD
16 ) with as short of a wavelength as possible,
as shown in Fig. 23.31, currently 405 nm.
• pumping of solid-state lasers, typically 910 or 940 nm for pumping Nd:YAG
• portable projectors, laser TV, entertainment.
• laser pointers, see Fig. 23.32. A red laser pointer simply uses the collimated red emission of a GaAsbased diode. In a green laser pointer, an infrared diode pumps a Nd:YAG or Nd:YVO 4 crystal. The
emitted beam is then frequency doubled, typically with a KTiOPO 4 (KTP) crystal.
• medical instruments with a variety of wavelengths in ophthalmology, dermatology, cosmetics (hair
removal, tattoo removal).
• various other uses, such as remote control, position detection, distance measurement, printing, scientific instrumentation.
The market for photonic devices is much more dynamic than the electronics market. An example is the
rapid change of dominating laser applications. For diode lasers, the two most prominent applications
are telecommunication (77% market share in 2000, 25% in 2003, 45% in 2008) and optical data storage
(17% market share in 2000, 60% in 2003, 44% in 2008).
23.4.3 Gain
Due to current injection,
17 a nonequilibrium carrier distribution is created. After fast thermalization
processes (phonon scattering), it can mostly described by quasi-Fermi levels. Sufficiently strong pumping leads to inversion, i.e. conduction-band states are more strongly populated with electrons than
valence-band states (Fig. 23.33). In this case, the stimulated emission rate is stronger than the absorption rate (cf. Sect. 10.2.6). The thermodynamic laser condition (cf. (10.23)) requires the difference of
16 16 million 405 nm laser diodes were shipped in 2006–2008. 85% of those are built into SONY’s PS3, the rest into
HD-DVD and other Blu-ray™disc (BD) players.
17 or due to optical pumping. If electrical contacts are not available, the laser action can be invoked by supplying a
high-intensity light beam, possibly in a stripe-like shape. For optically pumped semiconductor lasers see Sect. 23.4.15.