MULTIBAND SENSOR USING THICK HOLOGRAPHIC GRATING FOR SULFUR DETECTION BY LIBS

1. MULTIBAND SENSOR USING THICK HOLOGRAPHIC GRATING FOR SULFURDETECTION BY LIBS Photon etc. inc., 5795 Avenue de Gaspé #222, Montréal, Canada Industrial Materials Institute, NRC Canada, Boucherville, Canada

2. Introduction • Thick Holographic Grating • Optical and Mechanical Design of LIBS Detection Sensor • Built-in Custom Gating and Detection • Prototyped Concept • Proof of Concept and Conclusion

3. INTRODUCTION Increasing need for multiband detection by LIBS Few predetermined bands are required We propose a novel multiband sensor using thick holographic gratings Preliminary study on sulfur’s NIR lines in order to evaluate its performance. Atomic emission spectrum of sulfur from 150nm to 1µm

4. Thick holographic gratings are resonant optical elements (non dispersive) VBG in PTR glass used to producehigh-end spectroscopy instruments THICK HOLOGRAPHIC GRATING

5. OPTICAL AND MECHANICAL DESIGN OF LIBS DETECTIONSENSOR Mechanical Design

6. OPTICAL AND MECHANICAL DESIGN OF LIBS DETECTIONSENSOR ReflectionGrating Design

7. Photodiode • Photodiode • Amplifier • Amplifier • Comparator • ADC • FPGA • µC • USB Comm ∫ BUILT-IN CUSTOM GATING AND DETECTION High Sensivity Signal Acquisition and Digitization High-Speed Integrator and Trigger Sync. High-PrecisionGating (Photonic trigger)

8. PROTOTYPED CONCEPT

9. Experimental setup 1/3 Hz, 25 mJKigreNd:YAG laser Standard uncoated 250 mm focal lens Manual X-Y-Z linear stage Laptop using USB link to the sensor Prototyped multiband sensor PROOF OF CONCEPT AND CONCLUSION

10. Experimental plan Samples: compressed avicel / lactose powder containing 0%, 1%, 2% 2.5% and 3% of sulfur Atmospheric conditions: Ambient air 25 laser shots on each sample Random sample acquisition Use of photonic trigger only (no external trigger) Direct collection of plasma light Analysis method 5 groups of data Each group corresponds to the average of 5 consecutivemeasurements The calculation of LOD wasperformedaccording to the IUPAC definition 4 differentscases PROOF OF CONCEPT AND CONCLUSION

11. Results PROOF OF CONCEPT AND CONCLUSION LOD = 0.74% As per IUPAC

12. Results PROOF OF CONCEPT AND CONCLUSION LOD = 0.6% As per IUPAC Comparative measurementtakenwith a PharmaLIBS250 havingCzerny-Turner configuration and interline readout scientific grade CCD on the same bands shows a LOD of 0.2% (www.pharmalaser.com)

13. Conclusion Report uses of PTR glass VBGs in a LIBS multiband detection sensor Sensitive concept: LOD of 0.6 % on sulfur using NIR bands compared to 0.2% with high-end system Compact sensor: Non-dispersive technology and double-pass optical design on central lens Autonomous sensor: Built-in spectral filtering, detection and gating Inexpensive concept: Uses of VBG and Si photodiode Further improvement on LOD could be obtained : By tuning the electronics Prototyped concept close to deployment for sulfur detection Future version could use multiple VBS’s for multi-elemental analysis: Each band configurable from 400nm to 2500nm PROOF OF CONCEPT AND CONCLUSION