Quarktet
has acquired the full ownership of the GCLAD patent! See News for details.
Airborne acoustic waves create
changes in the air's density. This is the general description of a
sound
wave. The changes in density also produce changes in the air's index
of refraction. A light beam travelling through this section will
deflect slightly from its intended path. A position-sensitive
photodetector that
receives the light beam could translate the acoustic signals into
electrical signals without any mechanical components. This is the
concept of Gas-coupled Laser Acoustic Detection, or GCLAD.
This type of detection has been
demonstrated
before as the light travelled through acoustic fields in liquids or
solids,
but I was the first to demonstrate this property in air. Since the
discovery,
the instrumentation has evolved such that highly resolved waveforms
have
been detected in both the ultrasonic and audio frequency ranges.
As of December 10, Quarktet has
rebuilt
the GCLAD instruments in our Laboratory. To the best of our
knowledge,
this is the only GCLAD test bed in operation today. The system
will
be used to investigate new optical, mechanical, and electrical designs
that
will further enhance the capabilities and sensitivity.
Ultrasound
GCLAD was developed at the
University
of Delaware as an alternative method to detect ultrasound after it has
been
transmitted through a solid material, primarily for composite
materials.
This technique was incorporated into our laser-based ultrasound system.
Laser Ultrasonics (or Laser-based
Ultrasound) is the generation and detection of ultrasonic waves with
lasers. When a laser pulse strikes a material, the material converts
the light energy into thermal energy causing the material to locally
expand near the impact point. This expansion creates the ultrasonic
wave. There are several ways to detect the wave once it has passed
through the material. Typically these methods reflect a laser
beam off of the surface of the
material. The reflected light is gathered in an interferometer
which
then converts that to an electrical signal.
These
techniques have one major disadvantage, the system is inherently
dependent
on the optical qualities of the system. They function really well
on
mirror-like surfaces, and not-so-well on others. With GCLAD, the
detection
beam never touches the surface, so it works well on all types of
materials. GCLAD also requires no electro-optic stabilization, or
fine-tuning. A general setup is shown below
