A filtered optical feedback cavity ring down (FOF-CRD) technique employing a continuous wave Fabry-Perot diode
laser is employed to measure the total optical losses, i.e., absorption and scattering in optical components with arbitrary
thickness. The FOF from the ring down cavity (RDC) is re-injected into the oscillator cavity of the diode laser, and the
coupling efficiency of the laser into the RDC is significantly enhanced due to the FOF effect. An optical component
having parallel optical surfaces is inserted exactly normal to the light beam in the RDC. The optical losses of the
component are obtained from the change in the ring-down time of the RDC containing the component with respect to
that of the empty RDC. The measurement results for different samples are in good agreement with conventional laser
calorimetry data. The experimental results have demonstrated that the FOF-CRD technique is simple, inexpensive and
fast for measuring optical losses of optical components used in high-power laser system.
Cavity ring-down (CRD) techniques based on measuring the rate of decay of light intensity inside the optical cavity,
are widely used for trace gas analysis and high reflectivity measurement. In this presentation a filtered optical feedback
CRD (FOF-CRD) technique employing a multi-longitudinal-mode continuous-wave diode laser is investigated for
measuring high reflectivity of high reflective mirrors. The original spectrum of the diode laser without the effect of FOF
has two longitudinal modes covering tens of the free spectral ranges (FSR) of the ring down cavity (RDC). Due to the
relatively broadband spectrum, the theoretical efficiency of coupling the laser power into the RDC is less than 0.05%. In
the FOF-CRD scheme, on the other hand, the FOF induced overall spectrum broadening is experimentally observed,
with the diode laser running with several longitudinal modes. However the bandwidth of each longitudinal mode is
significantly reduced. The coupling efficiency of the laser power into the RDC is higher than 20% in FOF-CRD
technique. The enhancement of the coupling efficiency induced by the FOF effect is nearly three orders of magnitude.
High accuracy measurements of high reflectivity are achieved with this simple FOF-CRD scheme.
The absorptance and high reflectance measurements of laser optics are presented. In the absorptance measurement, the
laser calorimetry (LC) technique is investigated. A rigorous theoretical model describing the laser irradiation induced
temperature rise in a coated sample, in which both the finite thermal conductivity and the finite size of sample are taken
into account, is developed to optimize the temperature detection geometry to further improve the accuracy of the
absorptance measurement. For the high reflectivity measurement, an optical feedback cavity ring-down (OF-CRD)
technique, in which a continuous-wave (CW) Fabry-Perot (FP) diode laser is used as the light source, is employed for
high reflectivity measurement. The linear and V-shaped schemes are investigated to measure the reflectivity of cavity
mirrors and planar test mirrors, respectively. For cavity mirrors with reflectance larger than 99.99%, the measurement
error is less than 1ppm.