Page 177 - Tunable Lasers Handbook

156 Charles Freed

WAVE NUMBER Icm-')
iW00 3OlO0 20,OO 16pO 127 10p. 81" 7y
:: 31,j

I-
MBE GROWTH LATTICE-MATCHED TO PbTe SUBSTRATES
DOUBLE HETEROJUNCTION; SINGLE 300 8 QUANTUM-WELL
STRIPE WIDTH: 16-22 pm; CAVITY LENGTH: 326-460 urn
L I I I I I I

discontinued further development of lead-salt lasers shortly after the spin-off by
Laser Analytics. A periodically updated list of review articles and IR laser spec-
troscopy applications and techniques may be obtained from the company.
The remainder of this section describes two high-resolution spectroscopic
applications of TDLs in conjunction with the line-center-stabilized CO, (or CO)
lasers. Figure 25 illustrates a calibration method for locating and precisely cali-
brating reference lines that was used to determine the absorption spectra of UF,
isotopes in the vicinity of 12 ym [145,98]. In this experimental arrangement, a
beamsplitter combines the output of a lead-salt TDL and that of a 14C1602 laser.
A fast HgCdTe varactor photodiode [74] heterodynes one part of the combined
radiation, the beat note of which is displayed and measured by a microwave
spectrum analyzer (or frequency counter). The other part of the combined laser
radiation is used to probe an absorption cell that, in this particular experiment, is
filled with NH, gas at a pressure of 5 Torr. With the CO, laser stabilized to its
line center and the diode laser locked to the absorption line to be measured, het-
erodyne calibration provides an accuracy not currently available by any other
method. As an example, Fig. 26 shows a heterodyne beat frequency of 6775
MHz between a llCl60, laser and a diode laser tuned to one of the NH, absorp-
tion lines near 12.1 pm T145,98].