Characterization of Laser Eyewear Using Varying Pulse Conditions and Wavelengths

Transcription

1 Characterization of Laser Eyewear Using Varying Pulse Conditions and Wavelengths Michael D. Thomas, Andrew Griffin Spica Technologies Inc. 18 Clinton Dr. #3 Hollis, NH Bonnie Simmons Kentek Corporation 32 Broadway Pittsfield, NH 03263

2 Important To Understand Short Pulse Effects On Laser Absorbing Dyes Original title implied testing solely at 200 fs Revised goal of the effort was to identify dyes which may saturate using pulses < 1ns Implement laser tools in our laboratory that provide short pulses. Includes multiple wavelengths and multiple pulse widths. Effect of the saturation and the validity of using the EN 207 M rating as a blanket for all pulse widths over the range of 10fs-1ns.

3 Choose Laser Systems Which Provide Proper Data Set 2 wavelengths chosen because of laser pulse width range Many laser blocking filters can not be measured on a spectrophotometer due to high optical density Important to have equivalent long pulse system to make initial measurements 800 nm Ti:Al 2 O 3 15 ns / 200fs 1064 nm YAG Laser Source 6 ns / 600ps / 6 ps

4 Variance In Pulse Width Requires Different Experimental Procedures Longer pulses can be measured accurately with fast oscilloscope and known calibrated filters (High energy, low average power) Short pulse measurement methodology require sensitive, integrating power meter (Lasers are typically low energy moderate average power)

5 Experimental Setup For Longer Pulse Testing

6 Optical Density Measurement Procedure Adjust collimator to provide proper spot size at test plane Adjust attenuator to provide proper fluence in test plane Place calibrated neutral density filters in test plane and measure peak voltage f(od) for various filters.

7 Data Analysis And Measurement Use linear regression to generate equation of line Place unknown sample at test plane. Measure and average desired number of pulses using digital oscilloscope Place unknown sample in beam and measure voltage proportional to the transmitted laser energy Calculate Optical Density

8 Experimental Setup For Extreme Short Pulse Testing Similar to long pulse testing schematic Integrating sphere replaced with silicon photodetector Known (measured) attenuator placed in beam (not absorbing) Power on photodetector measured with known attenuator and sample in place Absolute transmission calculated

9 Laser Parameter Overview Pulse Width/Amplitude Measurement

10 Laser Parameter Overview Measurement Employees Gaussian Beam

11 Beam Profiles For Lasers Used In These Measurements

12 Different Samples Chosen To Represent Range Of Protective Materials Attenuating glasses Dye in polycarbonate Comingled dye for multiple wavelength applications Dye in acrylic Dye sourced overseas Novel nanoparticle (high VLT) dyes

13 Measurement Procedures 1064 nm Samples measured using spectrophotometer Samples measured using 6ns, 600 ps and 6 fs pulsed lasers. Samples measured at various fluence levels at each pulse width.

14 Measurement Procedures 1064 nm Samples measured using Spectrophotometer Samples Measured using 6ns, 600 ps and 6 fs pulsed lasers. Samples measured at various fluence levels at each pulse width.

15 Optical Densities Various Filters 6 ns (±.07 OD)

16 Optical Densities Various Filters 600 ps (±.1)

17 Optical Densities Various Filters 6 ps

18 Optical Density Measurement 6 ns/600ps

19 Optical Density Various Filters 15 ns (800 nm)

20 Optical Density Various Filters 200 ps (800 nm) Optical Density Various Filters 15 ns (800 nm)

21 Conclusion Certain dyes exhibit severe bleaching when irradiated as higher fluences and shorter pulse widths Glasses stable at 1064 nm down to 7 ps. Some variability at 200 fs Is this real or in noise Eyewear manufacturers should be aware of these instabilities EN 207 M range may not be sufficient to properly characterize short pulse eyewear.