|
Interference mechanism of laser disturbing infrared detector is analyzed. The disturbing grade was
separated into four levels according to interference effect. The levels are saturation, melting,
vaporization and plasma. The responsivity of a detector will drop and it can’t work effectively when it was saturated. Its performance wills recovery when the interference disappeared. Melting, Vaporization
and plasma will lead to permanent damage. The main damage to detector is thermal damage for
induced laser. The reason is that the detector will melt or evaporate when it absorbed the energy of induced laser. For HgCdTe detector, the damage appeared as Hg precipitation. It appeared as In exfoliated from welding outlet line of HgCdTe crystal or HgCdTe melting when the temperature of detector is higher. Since Vanadium Oxide has reversible transformation characteristic between
semi-conductor, metal and insulator, it can be used to protect detector from laser damage. Vanadium Oxide can be made as thin film coatings on optical system to protect the detector. the phase transformation point temperature of VO2 is 68°C,a few doping method can decrease the transformation
temperature. These mean that less energy can make VO2 film’s temperature increase to transformation
point. VO2 film protecting HgCdTe detector was used as an example to estimate the protection effect.
For an HgCdTe detector, its responsivity will drop two orders of magnitude when its temperature raises 70K. This case be regard as that the detector was disturbed. When a CO2 pulsed laser beam with 0.1μ
s∼10μs pulse width was incidence an HgCdTe detector, its heat conduction depth is 0.32∼3.2μm and its thermal diffusion can be ignored. The damage energy density threshold value is Ein=1.55J/cm2.
When CO2 pulsed laser beam incidence the detector through certain thickness VO2 film, the VO2 film
will has transformed from semiconductor state to metallic state before the laser beam damage the
detector. The energy of the laser beam will be total reflected. VO2 can be used as an intelligent preventer to protect detector against laser.
|
