Sol-Gel Glasses Doped with Pt-Acetylides and Gold Nanoparticles for Enhanced Optical Power Limiting

Abstract

High power laser pulses can be a threat to sensors, including the human eye. Traditionally this threat has been alleviated by colour filters that blocks radiation in chosen wavelength ranges. Colour filters' main drawback is that they block radiation regardless of it being useful or damaging, information is removed for wavelengths at which the filter protect. Protecting the entire wavelength range of a sensor would block or strongly attenuate the radiation needed for the operation of the sensor.Sol-gel glasses highly doped with Pt-Acetylide chromophores have previously shown high optical quality in combination with efficient optical power limiting through reverse saturable absorption 1 . These filters will transmit visible light unless the light fluence is above a certain threshold. A key design consideration of laser protection filters is linear absorption in relation to threshold level. By increasing chromophore concentration the threshold is lowered at the expense of higher linear absorption. This means that the user's view is degraded through the filter.Adding small amounts of gold nanoparticles to the glasses resulted in an increase in optical power limiting performance. The optimal concentration of gold nanoparticles corresponded to a mean particle distance of several micrometers. The work in this licentiate thesis is about the characterization and explanation of this effect.The glasses investigated in this work were MTEOS Sol-Gel glasses doped with either only gold nanoparticles of varying shape and concentration, 50 mM of PE2-CH 2 OH codoped with gold nanoparticles or 50 mM of PE3-CH 2 OH codoped with gold nanoparticles. The glasses only doped with gold nanoparticles showed high optical power limiting performance at 532 nm laser wavelength, but no optical power limiting at the fluences tested at 600 nm. The PE2-CH 2 OH glasses codoped with gold nanoparticles showed an enhancement of optical power limiting at 600 nm for the low gold nanoparticle concentration glasses. The enhancement was weak-1 Standard nomenclature, see section 1.3.3.iii iv ened or not present for higher concentrations. A similar enhancement above noise level for the PE3-CH 2 OH glasses was not found.A population model is used to give a qualitative explanation of the findings. The improvement in optical power limiting performance for the PE2-CH 2 OH glasses is explained by the gold nanoparticles helping to more quickly populate the highly absorbing triplet state during the rising edge of the laser pulse by enhancing two-photon absorption. The lack of any marked enhancement for the PE3-CH 2 OH glasses is explained by the PE3-CH 2 OH chromophore already being of sufficiently high performance to quickly populate the highly absorbing triplet state during the rising edge of the laser pulse. Further work is necessary to validate this model against other chromophores and improving its quantitative predictive power. Populärvetenskaplig sammanfattningLaserpulser med hög effekt kan vara ett hot mot sensorer, inklusive människoögat. Traditi...

Nonlinear materials for optical power limiting : characterization and modelling

“…", I've had ample opportunity to scrutinize our experimental methods. In my licentiate thesis I therefore had chosen to include a frank and thorough investigation of potential weaknesses in our previous OPL measurement protocol [1]. I also identified several potential pitfalls that I believed far too many workers in the OPL field ignored.…”

“…This thesis is in large parts based on my licentiate thesis [1], in particular chapter 1 and 4. Chapter 2 & 3 are a summary of article 4 [16], while also reusing parts of the licentiate thesis.…”

“…A distant 7 mm aperture functions as an alignment aid and beam clean-up. 1 3. A 3x Keplerian telescope is used to expand the beam.…”