Supercontinuum based mid-ir imaging Nikola Prtljaga workshop, Munich, 30 June 2017 PAGE 1 workshop, Munich, 30 June 2017
Outline 1. Imaging system (Minerva Lite ) wavelength range: 3-5 µm, 2. Scanning system wavelength range: 2 9 µm, b) Short wavelength system: 2-5 µm, c) Long wavelength system: 6 9 µm. PAGE 2 workshop, Munich, 30 June 2017
MINERVA Lite λ= 3 5 µm Imaging system PAGE 3 workshop, Munich, 30 June 2017
Imaging system basic concept Light Source Sample Image Y Image cube Wavelength λ 1 λ 2 Wavelength X Spectroscopic features of interest (well defined in broad spectral region) λ N Requirements: Narrow and fast wavelength selection Fast and high definition imaging G.Lloyd, N. Stone, Appl. Spect. 69, 1066-1073 (2015) PAGE 4 workshop, Munich, 30 June 2017
Imaging system basic concept Light Source Sample Image Y Hypercube Wavelength λ 1 λ 2 Wavelength X Spectroscopic features of interest (well defined in broad spectral region) λ N Requirements: Narrow and fast wavelength selection Imaging system Fast and high definition imaging G.Lloyd, N. Stone, Appl. Spect. 69, 1066-1073 (2015) PAGE 5 workshop, Munich, 30 June 2017
Imaging system - details NKT supercontinuum source Xenics camera G&H AOTF PAGE 6 workshop, Munich, 30 June 2017
Imaging system - details Supercontinuum source Spectral range: 1.8 4.5 µm Repetition rate: 2.5 MHz AOTF Spectral range: 2 4.5 µm Spectral resolution: 1-4 nm Camera Spectral range: 3 (1) 5 µm Resolution: 640 x 512 Pixel pitch: 20 µm Frame rate: 90 fps Equipment System Optical head Reflection Transmission Acquisition speed: 50 fps (limited by frame grabber) Field of view: 3 mm Pixel resolution: 5 µm Actual resolution: 30 µm (limited by optics simple refractive optics) PAGE 7 workshop, Munich, 30 June 2017
Imaging system Visible image Supercontinuum light is coherent. Coherence is largely preserved in the single mode fiber. Speckle occurrence in biological issues Mid-IR image Multimode input : Speckle suppressed (Residual ~ 10 %) Zoom in PAGE 8 workshop, Munich, 30 June 2017
Imaging system Comparison with commercial system Paraffinated sample Frozen sample Spatially averaged to reduce the speckle. Scanning system introduced to solve speckle issue and extend the spectral range. There is a penalty in acquisition speed (imaging system acquires full spatial and spectroscopic information in matter of seconds). PAGE 9 workshop, Munich, 30 June 2017
MINERVA λ= 2 9 µm Scanning system PAGE 10 workshop, Munich, 30 June 2017
Scanning system basic concept Light Source Sample Image Y Image cube λ 1 Wavelength λ 2 λ N x 0,y 0 x 0,y 0 Y Wavelength X Image cube x 0,y 0 Wavelength Position λ 1 λ N x 1,y 0 X Significantly slower than imaging. x N,y N PAGE 11 workshop, Munich, 30 June 2017
Scanning system short λ PAGE 12 workshop, Munich, 30 June 2017
Scanning system short λ Piezo scanner Step time: 30 ms Range: 800 x 800 µm Visible camera Field of view: 800 x 640 µm Pixel resolution: 0.6 µm Actual resolution: 4 µm Detector Spectral range: 1.5 4.8 µm Bandwidth: 10kHz Cassegrain objectives Magnification: 15x NA: 0.3 Software LabVIEW on Windows Optical head Data saved as.png image 1 step = 1 pixel GUI System 16 ms per point acquisition time (non-deterministic OS) PAGE 13 workshop, Munich, 30 June 2017
Scanning system short λ Sample 1 Multimode input Sample 2 Mid-IR image @ 3µm Mid-IR image @ 3µm 3D representation Area size: 600µm x 600µm Pixel resolution: 5µm Time averaging: 10ms No speckle spatial averaging Current work: Testing Building larger data set. PAGE 14 workshop, Munich, 30 June 2017
Broadband system scheme Coloured elements are interchangeable depending on the wavelength requirements 2-4.5 µm 2-4.5 µm Source AOTF Single point detector + Lock-in (Short λ SC) Source (Long λ SC) (Short λ) Reflective optics (Collimation and focusing) Sample with fast X-Y motion Reflective optics (Collimation and focusing) (Short λ) Spectrometer + Array detector 6-9 µm (Long λ) 6-9 µm PAGE 15 workshop, Munich, 30 June 2017
Scanning system long λ Experiment conducted at DTU Visible image λ = 6030 nm λ = 6450 nm Technical difficulties lead to limited data set Area size: 600µm x 600µm Pixel resolution: 5µm Time averaging: 100ms Demonstrated supercontinuum imaging above 5µm. PAGE 16 workshop, Munich, 30 June 2017
Conclusions Supercontinuum source is a viable option for imaging in Mid-IR. In combination with the AOTF and the camera, it allows for very fast data acquisition (~s). Speckle is an issue when used system is used in the imaging mode. Spatial averaging solves the speckle issues. Further development needed for operation above 5 µm. PAGE 17 workshop, Munich, 30 June 2017
Thank you for your attention. PAGE 18 workshop, Munich, 30 June 2017