This document summarizes research on measuring scattering losses of laser components using the Total Integrated Scattering (TIS) method with different beam diameters. The study found that using smaller beam diameters (less than 0.4mm required by standards) increased the resolution of surface maps but also increased measurement durations and scattering loss values. Smaller beams made smaller defects and damages more visible. Beam diameters from 0.2mm to 1.12mm produced scattering loss measurements that varied within ±10% and are suitable for measurements.

1. MEASUREMENT OF SCATTERING LOSSES OF LASER COMPONENTS BY TOTAL INTEGRATED SCATTERING METHOD USING DIFFERENT BEAM DIAMETERSS.Liukaitytė, V. Sirutkaitis Quantum Electronics Department, Vilnius University, Saulėtekio ave. 9 – III, LT – 10222 Vilnius, LithuaniaSimona.Liukaityte@ff.stud.vu.lt Introduction Scattering looses is one of the factors that limit quality of optical components [1]. The scattering of the optical component is caused by : surface topography, surface contamination, bulk index fluctuations, and bulk particulates . Light scatter is proving to be an ideal method to get information about surface, because it is fast, noncontact, and performs well on very smooth surfaces [2]. The measurement principle of Total Integrated Scattering (TIS) described in International Standard ISO 13696:2001 is based on an Ulbricht sphere as the integrating element for scattered radiation and cw laser [3]. This work explores modified TIS measurement scheme based on repetitively Q-switched laser source. The main aim of this work was evaluation of the influence of the laser beam diameter on the TIS measurement accuracy and roughness estimation of the polished substrates. Experiment The measurementswere taken in the tight box which protects measuring area outside light. The box meets 6th ISO cleanroom class as special air filtrers are used. Air filters clean the air and reduces Rayleigh and Mi scattering influence for the measurement. An integrating Ulbricht sphere is employed for the collection and integration of the radiation scattered by the sample. The Ulbricht sphere is standard scattering sphere coated with suitable light–scattering surface and fitted with a suitable detector for the wavelength of interest. The scattered signal was registered by Hamamatsu H5784-20 photomultiplier which sends a signal to the computer. A diffuse reflectance standard is used for calibration of the detector signal. The standard total reflectance is more than 98%. The laser beam is focused to the investigated sample by the 1 m focus lens. The scanning of the samples in two axes was performed. This allowsto make a map of surface scattering. Measurement of TIS was based on 1 kHz repetition rate Q-switched laser and capable to perform measurements at 532 nm and 355 nm wavelengths (the maximum pulse energy at 532 nm is – 0.9 mJ, at 355 nm is 0.6 mJ). ISO 13696:2001 requires that laser beam diameter on the measured surface would be larger than 0.4 mm for correct surface roughness estimation. Measurements in this work were taken using four different diameters – some of them bigger (up to 1.12 mm) and some smaller (0.2 mm) than required by the standard. The mirrors with high coefficient of reflection’s beam for scanning were used for research. Experiment setup Results Scattering losses of the entire mirror surface measured using different beam diameters are presented in the Figure 1. When the beam diameter was reduced, maximum, mean and standard deviation of scattering results grew up, minimum and median of scattering results reduced. Results of surface roughness correlate with results of scattering. The maps of surface roughness made using different beam diameters are presented in the Figure 2 and Figure 3. A decrease of the beam diameter allows to make the surface roughness map with better resolution. It is possible to find more precise coordinates of maximum and minimum values of scattering losses. Conclusions 1. A decrease of the beam diameter increases resolution of the scattering centers, but increases the duration of the measurements. 2. With an increase of resolution smallerdefects and damages becomevisible. 3. The usage of beam diameters from 0.2 mm to 1.12 mm changes average scattering losses in the range of ±10% and can be used in measurements. Fig. 1 Scattering losses of the entire mirror surface measured using different beam diameters. λ = 532 nm Fig. 3 Surface roughness of the entire mirror using different beam diameters.λ = 532 nm Fig. 2 Surface roughness of the entire mirror using different beam diameters.λ = 355 nm References [1] J.C. Stover, OpticalScattering: MeasurementandAnalysis, S P I E-InternationalSocietyforOpticalEngineering, Bellingham, Washington, USA, 1995. [2] M. Maciulevičius, Optinių dangų ir lazerinių elementų švesos sklaidos tyrimai plačiame spektro ruože, Daktaro disertacija, Vilniaus universitetas, Vilnius, 2009. [3] I.O.f. Standardization, International Standard ISO 13696, Opticsandopticalinstruments - Testmethodsforradiationscatteredbyopticalcomponents, Geneva, Switzerland, 2002.