Page 261 - Handbook of Lasers

Section 1.4
COLOR CENTER LASERS

1.4.1 Introduction
The optically active centers in color center lasers are various types of point defects (i.e.,
color centers) in alkali halide and oxide crystals. The color centers are generally produced by
ionizing radiation or are thermally induced. Additional ions may be present to stabilize the
defect center and are included in the description of the active center. Other lasers in this
-
category are based on vibrational transitions of molecular defects, such as CN .

Color center lasers are usually excited by optical pumping with broadband or laser
radiation. Lasing involves allowed transitions between electronic energy levels, hence the
gain can be high. Color center lasers have been reported that operate in the wavelength range
from approximately 0.4 to 5 mm. Due to their large homogeneous emission bandwidths,
color center lasers have varying degrees of tunability. The tuning ranges of some of the
longer-lived alkali halide color center lasers are shown in Figure 1.4.1.

The output of color center lasers may be cw or pulsed. Representative average powers and
average energies of cw and pulsed color center lasers in alkali halides are summarized in Ref.
73. As in the case of paramagnetic ion lasers, picosecond pulses can be obtained using
various mode-locking techniques and femtoseconds pulses using saturable absorbers. The
operative lifetimes of the color centers in these lasers depend on the temperature and can vary
from hours to years. Many color center lasers require operation at low temperatures.

Further Reading
Baldacchini, G., Optical excitation and relaxation of solids with defects, in Spectroscopy and
Dynamics of Collective Excitations in Solids, Di Bartolo, B. Ed., Plenum Press, New
York (1997), p. 495. (This paper contains an interesting history of color center and color
center laser research.)

Basiev, T. T. and Mirov, S. B., Room Temperature Tunable Color Center Lasers, Vol. 16
of Laser Science and Technology Series, Gordon & Breach, New York (1994), p. 1.

Basiev, T. T., Mirov, S. B., and Osiko, V. V., Room-temperature color center lasers, IEEE
,

J. Quantum Electron. 24 1052 (1988).

Gellermann, W., Color center lasers, J. Phys. Chem. Solids 52, 249 (1991).
German, K. R., Color Center Laser Technology, in Handbook of Solid-State Lasers, Cheo,
P. K., Ed., Marcel Dekker, New York (1989), p. 457.

Mirov, S. B. and Basiev, T., Progress in color center lasers, in Semiconductor Lasers,
Selected Topics in Quantum Electronics 1 (June 1995).

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