Page 321 - Tunable Lasers Handbook

6 Transition Metal Solid-State Lasers 281

Flashlamp-pumped laser performance of Co:MgF,, Ni:MgF,, and VMgF,
have all been achieved at cryogenic temperatures [56]. V!MgF2 did little more th&
achieve threshold. Even at cryogenic temperatures, the threshold for flashlamp-
pumped operation occurred at flashlamp energies of about 1150 J. Part of this high
threshold is associated with the low concentration of V in the sample. On the other
hand, thresholds for Ca:MgF, and Ni:MgF, devices were achieved at somewhat
lower flasMamp energies, around 690 and l<O J. respectively. Slope efficiencies for
these materials were not quoted. Peak emission wavelengths were 1.750 and 1.623
pm for these two laser materials.
Laser-pumped performance of Co:MgF, has been achieved at temperatures
up to room temperature. Laser pumping can utilize a Nd:YAG laser operating at
1.33 pm [62]. As an example, with an output mirror reflectivity of 0.98 and at a
temperature of 248 K. slope efficiencies of 0.59 have been achieved for both x
and CT polarizations. The threshold for the 0 polarization was 17 mJ. whereas
threshold for the x polarization was 27 mJ. At a temperature of 299 K, slope effi-
ciencies of the 0 and x polarizations decreased to 0.48 and 0.39, respectikely.
Thresholds increased to 28 and 41 mJ at this temperature for the two polariza-
tions. To achieve this performance, low-loss laser material was essential to
achieve the low threshold and high slope efficiency. Note that the high slope effi-
ciency was achieved despite the high output mirror reflectivity. Using laser pump-
ing, cw operation has been achieved in both Co:MgF, and Ni:MgF, [63,64].
Dr. Peter Moulton kindly provided figures for this subsection, some of
which have not been published previously.

10. WAVELENGTH CONTROL METHODS

Most applications of transition metal solid-state lasers benefit from the tuning
characteristics of these devices. However, to capitalize on the tuning characteris-
tics, wavelength control devices are needed. Wavelength control of solid-state
lasers falls into three general categories: broadband wavelength control. narron -
band wavelength control, and injection wavelength control. For broad tuning.
only a coarse wavelength control device is required. It may be ncted that with
lanthanide series lasers, broad wavelength control devices are usually not
required. Broad wavelength control devices include prisms, gratings, and bire-
fringent filters. With these devices. the spectral bandwidth of the transition metal
laser can be reduced to the order of a nanometer. For narrow tuning. a narrox.
n avelength control device must be utilized in addition to the broad wavelength
control device. Narrow wavelength control devices are primarily etalons. The
transmission peaks of these devices are approximately cyclic with u avelength.
so they are usually used in conjunction with a broad wavelength control device.
With these devices, the spectral bandwidth of the transition can be reduced to Lhe
order of a picometer or less. With injection control, a narrow spectral bandwidth