Black optical coating for high-power laser measurements from carbon nanotubes and silicate.

We describe a coating based on potassium silicate, commonly known as water glass, and multiwall carbon nanotubes. The coating has a high absorbance (0.96 at 1064 nm in wavelength) and a laser damage threshold that is comparable to that of ceramic coatings presently used for commercial thermopiles for high-power laser measurements. In addition to a potassium silicate-based coating we discuss sodium silicate, lithium silicate, and a commercially available ceramic coating. We document the coating process and experiments that demonstrate that the laser damage threshold at 1064 nm is 15 kW/cm(2).

Reflective attenuator for high-energy laser measurements.

A high-energy laser attenuator in the range of 250 mJ (20 ns pulse width, 10 Hz repetition rate, 1064 nm wavelength) is described. The optical elements that constitute the attenuator are mirrors with relatively low reflectance, oriented at a 45 degrees angle of incidence. By combining three pairs of mirrors, the incoming radiation is collinear and has the same polarization orientation as the exit. We present damage testing and polarization-dependent reflectance measurements for 1064 nm laser light at 45 degrees angle of incidence for molybdenum, silicon carbide, and copper mirrors. A six element, 74 times (18 dB) attenuator is presented as an example.

Foam-based optical absorber for high-power laser radiometry.

We report damage threshold measurements of novel absorbers comprised of either liquid-cooled silicon carbide or vitreous carbon foams. The measurements demonstrate damage thresholds up to 1.6x10(4) W/cm(2) at an incident circular spot size of 2 mm with an absorbance of 96% at 1.064 microm. We present a summary of the damage threshold as a function of the water flow velocity and the absorbance measurements. We also present a qualitative description of a damage mechanism based on a two-phase heat transfer between the foam and the flowing water.

Optical trap detector for calibration of optical fiber powermeters: coupling efficiency.

The optical trap detector is based on two, 1 cm x 1 cm silicon photodiodes and a spherical mirror contained in a package that is highly efficient for measuring light diverging from the end of an optical fiber. The mathematical derivation of the coupling efficiency relies on the integral directional response weighted by the angular intensity distribution of an idealized parabolic optical beam. Results of directional-uniformity measurements, acquired with the aid of a six-axis industrial robotic arm, indicate that the trap has a collection efficiency greater than 99.9% for a fiber numerical aperture of 0.24. Spatial uniformity measurements indicate that the variation of detector response as a function of position is less than 0.1%. The detector's absolute responsivity at 672.3, 851.7, and 986.1 nm is also documented by comparison with other optical detectors and various input conditions and indicates that the design is well suited for laser and optical fiber power measurements.