Simultaneous mapping of reflectance, transmittance and optical loss of highly reflective and anti-reflective coatings with two-channel cavity ring-down technique

Abstract

We demonstrate the use of a two-channel cavity ring-down (CRD) technique for simultaneously measuring/mapping the reflectance R, transmittance T and optical loss L (absorption plus scattering losses) of highly reflective (HR) and anti-reflective (AR) laser components. High reflectance/transmittance of HR/AR components is measured with the ring-down time of CRD signals, while the low residual transmittance/ reflectance of HR/AR components is determined by the amplitude ratio of two CRD signals, and the optical loss is then determined via L = 1-R-T. Experiments are performed to measure and map R, T, and L of HR mirrors with different transmittance levels from below 1ppm to about 70 ppm (part-per-million) and of one AR window at 635nm. For a 4 ppm-transmittance HR mirror, the measured R, T, and L at one position are 99.99821 ± 0.00004%, 4.042 ± 0.008 ppm and 13.9 ± 0.4 ppm, respectively. For the AR sample, the measured T, R, and L at one position are 99.99279 ± 0.00004%, 50.0 ± 0.7 ppm and 22.0 ± 0.4 ppm, respectively. The sub-ppm standard deviations for R, T, and L indicate the high accuracy of the two-channel CRD technique for the simultaneous measurements of reflectivity, transmittance and optical loss of HR and AR components. High-resolution mappings of R, T, and L of both HR and AR samples are demonstrated. The simultaneous measurements/mappings of reflectance, transmittance, and optical loss with sub-ppm accuracy are of great importance to the preparation of high-performance laser optics for applications such as gravitational-wave detection and laser gyroscopes.

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors

“…Cavity ring-down (CRD) spectroscopy was used for a precise determination of the reflectance of the mirrors at 355 and 532 nm, respectively. , The measurement was performed on the mirrors deposited on the fused silica substrates of dimension 25 mm × 25 mm × 3.05 mm using Layertec’s custom-built CRD setup. Therefore, a pulse from an EKSPLA NT242 SH+SFG OPO is coupled into an optical cavity consisting of two highly reflecting mirrors.…”

Advance on transmittance measurements methods

“…The transmittance is expressed as, At the same time, the folded cavity can also be used to measure the transmittance of the diaphragm (Fig. 5) [25] , in which, 1 R and 2 R are the cavity mirror, 3 R is the high-reflection mirrors with known transmittance, L is a lens and p is a polarizer.…”

Near-infrared scanning cavity ringdown for optical loss characterization of supermirrors

“…For the sample size of 100 repeated measurements, the standard error of the mean provides a precision of 0.01 ppm, but drifts begin to become apparent at this level. We hypothesize that the difference in statistics is driven by the spatial mode stability of the 1064 nm diode laser under optical feedback since this is known to be a strong contributor to the measurement noise [11,12]. In Figure 2(b), we explored the spatial reproducibility by repeating measurements over a particular high-loss feature.…”