Page 327 - High Power Laser Handbook

296 So l i d - S t at e La s e r s Heat-Capacity Lasers 297

• 64 high-powered diode arrays at 84 kW of average output
power per array and a duty cycle of 20 percent
These parameters follow the aforementioned general power scal-
ability formula for a heat-capacity laser: increasing the number of
laser gain media, increasing the size of the laser gain media, and
increasing the duty cycle of the high-powered diode arrays.
Although many details of the entire laser system’s architecture
remain to be resolved, there is no fundamental reason that the HCL
cannot attain megawatt-class output power using the same nominal
architecture that is currently used today. In addition, the only tech-
nology that has not been physically demonstrated to date is the
20-cm transparent ceramic laser gain media. Thus, the “leap” to sig-
nificantly higher laser output power levels is more of an evolution-
ary engineering process, rather than a wait for a significant
technological breakthrough to occur.

11.6 Applications and Related Experimental Results
Because of its large output power capability, as well as its simple archi-
tecture resulting from the ease of operation and compact footprint, the
heat-capacity laser is often used to conduct a variety of laser-material
interaction experiments. Several investigations using the HCL at Law-
11
rence Livermore National Laboratory are cited to provide examples
of the various capabilities of the heat-capacity laser.
11.6.1 Rapid Material Removal (Boring/Ablation)
Experiments have been conducted that showed the laser interaction
on steel targets, initially in a static configuration. The collected data
are often represented by the term Q* (Q star), or the amount of energy
required to remove 1 g of material. In this particular experiment, a
25-kW beam produced by the heat-capacity laser, with a laser spot
size of approximately 2.5 × 2.5 cm and a pulse frequency of 200 Hz, is
impinged on a 1-in-thick block of carbon steel. The results of the laser-
target interaction after 10 s of continuous laser operation are shown
in Fig. 11.32. The initial hole through the steel block was generated
after just 6 s of runtime.
A significant amount of material was removed during this laser-
target interaction. This type of experimental data can be useful in
determining machining rates for laser cutting tools, as well as in esti-
mating burn-through times for targets of military interest.

11.6.2 Aerodynamic Imbalance Due to Airflow Interaction
The sequence shown in Fig. 11.33 shows an experimental simula-
tion of a laser beam interacting with a thin aluminum structure in
flight. The laser beam heats the material surface (13 × 13 cm spot