Gas-coupled laser acoustic detection (GCLAD) is a method for detecting acoustic waves based on optical beam deflection.  When an acoustic wave interacts with an optical beam, the refractive index gradient associated with the wave causes the beam to deflect.  We detect the deflection with a highly sensitive position sensitive detector (PSD).

Laser beam propagating perpendicular to an acoustic wave gets deflected by the refractive index gradient (grey) of the wave. The resulting deflection (Z) is recorded by a position-sensitive detector (PSD).

GCLAD is completely independent of the surface optical properties, therefore allowing for a fully non-contacting photoacoustic and laser-ultrasonic imaging system.  This opens up applications such as surgical guidance or imaging in situations where contact can cause harm or discomfort (such as burn diagnostics).

GCLAD was first developed for non-destructive testing, and we have recently characterized and developed GCLAD for medical imaging.  Furthermore, we have published the first photoacoustic images of tissue phantoms using GCLAD.

Left: Setup for photoacoustic (PA) imaging experiment.  A nanosecond pulse of light is absorbed by an optical absorber (mimicking hemoglobin) embedded in a tube 2 cm beneath the detection surface.  The GCLAD beam detects the PA wave 6 cm from the detection surface.  Right: reconstructed PA image.  Features 1 and 2 originate at the inner surface of the tube wall nearest the detection (1) and source (2) surfaces.