LINC: an Interdepartmental Laboratory at ENEA for Femtosecond CARS Spectroscopy

Transcription

1 LINC: an Interdepartmental Laboratory at ENEA for Femtosecond CARS Spectroscopy Mauro Falconieri ENEA FSN-TECFIS C.R. Casaccia via Anguillarese 301, Rome (Italy) LIMS Frascati May 17 th 2018

2 outline 1. the LINC project: a. motivation and basic ideas b. history c. ingredients 2. present status and first experimental results 3. planned work

3 1. a. motivations spectroscopy is an ubiquitous tool which can address many topics relevant for ENEA activities full exploitation of concentrated expertise and equipment is more efficient than the use of entry-level, sparse systems basic ideas sharing expertise and tools to address different topics by vibrational spectroscopy joint deployment of resources for the implementation of the project LINC: laboratorio interdipartimentale per la spettroscopia CARS

4 1. b. history August 2014: proposal for the development of a micro-cars system for bioelectromagnetism studies (M. Falconieri, C. Merla) February 2017: LINC proposal (M. Falconieri, M. Marrocco, C. Merla) February 2017: workshop «Prospettive per un laboratorio CARS al femtosecondo» (M. Falconieri, M. Marrocco, C. Merla) May 2017: feasibility study (M. Falconieri, M. Marrocco, C. Merla) November 2017: allocation of funds for LINC December 2017: purchase of optical and optomechanical components January 2018: set-up of the microcars March 2018: first CARS signal

5 1.c. ingredients vibrational spectroscopy: CARS ultrashort pulses & hyperspectral imaging topics of interest

6 ingredients: vibrational spectroscopy detection of vibrational frequencies associated to chemical bonds non-destructive techniques, fingerprinting, chemical mapping Raman scattering: inelastic scattering of photons due to interaction with vibrational modes P P (3) i (3) χ 0 (3) e E 3 E i A e i iwt third-order nonlinear process c.c. (3) (3) w D χ w ; w, w, w E w E w E w 4 Coherent Anti-Stokes Raman Scattering (CARS) 0 j, k, l ijkl 4 generation of a polarization at w 4 using three fields at w 1, w 2, and w 3 1 w 2 3 j 1 4 w1 w2 w3 k 2 l energy conservation 3 (four-wave mixing) w w w if S P vib vibrational resonance molecules driven into a vibrational state strong w AS w AS 2w P w S 3 fields at 2 different frequencies (w p = w p, w s ) are necessary to monitor a vibrational frequency w AS

7 I why CARS CARS Raman (3) w AS w AS I PI S N I PI I w Nz I S Raman wraman 0 process is nonlinear & coherent anisotropic emission superlinear dependence on laser power and sample concentration anti-stokes emission not influenced by fluorescence linear, spontaneous process isotropic emission incoherent signal fluorescence can be problem CARS signal can be much stronger than in spontaneous Raman

8 CARS & ultrashort pulses: imaging ultrashort pulses (t<10-12 s) high peak power high repetition rate Coherent MIRA 900-F ultrafast laser with pump laser t=80 fs Dt=13.6 ns r=76 MHz Kerr-lens mode-locked laser pulse train maximization of nonlinear effects high repetition rate measurements E pulse 10 nj P peak 80 kw P ave 0.8 W 720 nm λ 1020 nm imaging by CARS with ultrafast laser 40 mw on sample 50 ms/pixel 20 frame acquisition time (600X400 pixels) Parekh et al. Biophysical Journal 99, 2695 (2010) short acquisition time + intrinsic spatial resolution imaging by spontaneous Raman 1 s/pixel to avoid photodamage of biological materials

9 CARS & ultrashort pulses: multiplex CARS narrow bandwidth (ns) laser narrow bandwidth pump & probe large bandwidth Stokes single vibrational level addressed multiplex CARS: simultaneous measurement of vibrational bands a spectrally broad Stokes beam can be obtained by white light generation in a nonlinear Photonic Crystal Fiber (PCF) PCF vibrational spectra up to 3000 cm -1

10 ingredients: topics of interest FSN (Fusion and Technology for Nuclear Safety and Security Dept.) TECFIS division (Physical Technologies for Safety and Health): development of a micro-cars system as an advanced laser diagnostic tool applications : biophotonics, environmental diagnostics SSPT (Territorial and Production Systems Sustainability Dept.) TEC division (Technologies and methods for the protection of health): imaging of animal tissues and cells and their modifications caused by EM exposure (Caterina Merla) DTE (Energy Technologies Dept.) PCU division (Efficient Production, Conversion and Use of Energy): energy materials (ionic liquids, carbon allotropies), biofuels (Michele Marrocco)

11 outline 2. present status and first experimental results

12 2. experimental setup SOLAR LS2 monochromator + cooled PMT n mapping detection systems TRIAX 320 monochromator + EM CCD spectral CARS microscope optical layout single laser oscillator photonic crystal fibre FEMTOWHITE-CARS microscope optical interface ( low available energy) Kano et al. Appl. Phys. Lett. 86, (2005)

13 2. experimental setup microscope

14 Stokes beam characterization_1 in multiplex CARS the spectral width of the Stokes beam defines the measurable Raman band was 2w P ws the Stokes beam is derived from a supercontinuum whose spectral distribution depends on the phase dispersion (chirp) of the laser beam at the PCF input the laser chirp depends on the optical elements in the laser cavity and in the layout we purposely varied the chirp of the laser beam by controlled insertions of optical elements: optical isolator & objectives: positive chirp prism compressor: negative chirp we measured the spectrum of the supercontinuum in the range 600 nm-1200 nm using calibrated detectors

15 power spectral density (W/nm) power spectral density (W/nm) power spectral density (W/nm) Stokes beam spectral power density (W/cm -1 ) Stokes beam characterization_2 chirp was estimated from the measured autocorrelator pulsewidth of the beam at different points of the layout GDD MIRA (fs 2 ) t AC MIRA (fs) optical elements - 1.5x isolator+ compressor GDD@in OB1 (fs 2 ) t OB1 (fs) GDD@fiber in (fs 2 ) 3.5x x x compressor - 4.1x x x compressor - 6.1x x x10-4 attained chirp conditions GDD>0 7.5x10-4 supercontinuum total power: 18 mw 25 mw 35 mw 5.0x mw 52 mw 61 mw GDD»0 5.0x10-4 supercontinuum total power: 17 mw 23 mw 29 mw 33 mw 39 mw 43 mw 2.5x x10-4 GDD<0 5.0x x10-4 supercontinuum total power: 18 mw 23 mw 35 mw 50 mw 60 mw 68 mw 5x10-5 4x10-5 3x10-5 2x10-5 1x10-5 l=780 nm, supercontinuum power: 50 mw GDD>0 GDD 0 GDD< w Raman shift (cm -1 ) AS 2w w P S wavelength (nm) wavelength (nm) wavelength (nm)

16 Stokes beam modeling Supercontinuum generation was modeled using a published MATLAB code input parameters: PCF specifications and beam dispersion parameters the code was modified to account for the actual excitation beam chirp the model is capable to reproduce the major features of the experimental data the exact position of the supercontinuum bands, which depends strongly on the beam dispersion, is not always accurately predicted. work is in progress to improve the agreement by finely tuning the input parameters in order to exploit the predictive power of the modeling

17 Stokes spectral power density (a.u.) CARS signal (a. u.) Stokes spectral power density (a.u.) CARS signal (a. u.) CARS signal from bulk solvent the spectral distribution of the Stokes beam strongly influences the shape of the CARS signal: l exc =780 nm GDD»0 l exc =780 nm GDD>0 cyclohexane CARS cyclohexane CARS Raman shift (cm -1 ) Raman shift (cm -1 ) measured spontaneous Raman spectrum of cyclohexane the ratio of the two cyclohexane Raman bands is altered whenever the Stokes beam intensity is uneven

18 3. planned work outline

19 planned work coupling of microscope to optical layout implementation of software modules to control the experimental setup: mapping, signal and sample image acquisition test on inorganic samples (typically polystyrene&polymethylmethacrylate beads) test on biological tissues next month: project workshop at C.R. Casaccia

20 conclusions an internal project for the establishment of an interdepartmental laboratory for femtosecond coherent anti-stokes Raman spectroscopy was presented and funded the project exploits a multidisciplinary approach and a joint deployment of resources to address topics relevant for ENEA activities, such as energy materials characterization, biomedicine, and environmental safety using coherent vibrational spectroscopy the experimental setup of a micro-cars apparatus using a femtosecond oscillator was defined and realized and first CARS data have been measured on simple solvents next experimental work will be aimed to collection of hyperspectral Raman maps

21 people Mauro Falconieri, Michele Marrocco, Caterina Merla proposers Serena Gagliardi, Flaminia Rondino LINC crew Mahsa Ghezelbash (ENEA-ICTP grant) LINC guest starting 1 st June acknowledgments Roberta Fantoni for support and discussion Mario Tucci (DTE-FSN-TEF) for sharing some instrumentation contact: mauro.falconieri@enea.it