Page 21 - Tunable Lasers Handbook

4 F. J. Duarte

cavity compression [37]. Utilizing intracavity negative dispersion techniques,
Ti3+:Al,03 lasers have yielded 11 fs [381. Also, 62 fs have been reported in
OPOs using extracavity compression [39]. Emission from FELs is intrinsi-
cally in the short-pulse regime with pulses as short as 250 fs [17].

2. TUNABLE LASER COMPLEMENTARITY

From the data given previously it could be stated that tunable sources of
coherent radiation span the electromagnetic spectrum continuously from the near
ultraviolet to the far infrared. However, this claim of broad coverage is sustained
from a global and integrated perspective of the field. Further, a perspective of
complementarity is encouraged by nature, given that different sources of tunable
coherent radiation offer different optimized modes of operation and emission.
In this context, under ideal conditions, the application itself should deter-
mine the use of a particular laser [40,41]. This perspective should ensure the
continuation of the utilitarian function traditional of the early tunable lasers that
ensured their success and pervasiveness.
To determine an appropriate laser for a given application, the logic of selec-
tion should identify the simplest and most efficient means to yield the required
energy, or average power, in a specified spectral region. In practice, the issue
may be complicated by considerations of cost and availability. In this regard,
selection of a particular pulsed laser should include consideration of the follow-
ing parameters:
1. Spectral region
2. Pulse energy
3. Average power (or prf)
4. Cost (capital and operational)
5. Environment.

More subtle issues that are also a function of design include the following:
6. Emission linewidth
7. Wavelength and linewidth stability
8. Pulse length (femtoseconds, nanoseconds, or microseconds)
9. Physical and optical ruggedness
10. Amplified spontaneous emission (ASE) level.
A basic illustration of complementarity is the use of different types of lasers
to provide tunable coherent radiation at different spectral regions. For instance.
FELs can be recommended for applications in need of far-infrared emission,
whereas dye lasers are suitable for applications requiring high average powers in
the visible.