RAMAN SPECTROSCOPY practice, instrumentation and some tips José A. Manrique University of Valladolid Centro de Astrobiología

Basis of the effect

Excited electronic states fluorescence emission

Fluorescence: your enemy Fluorescence competes with Raman effect Organics, and impurities in the samples usually present fluorescence. It actually can cover the Raman emission Its a challenge that has been approached with very different and imaginative solutions

Parts of a Raman Spectrometer CCD Spectrometer + Raman probe Optics Laser

Parts of a Raman spectrometer Raman probe:

Dealing with CCD’s Not all the CCDs behave the same Not all the rows in a CCD have the same sensitivity Associated problems: noise, etaloning…

NIR Raman? How to deal with etaloning

Spectrometer Several types and several optical configurations with different performances and behaviours Is your device propperly calibrated? Don’t take it for granted

Optics for collection/focalization Raman spectroscopy is highly versatile: – Micro raman – Macro raman – Remote raman Instrumental function: different in every case

Laser Different types Not all the lasers are good for Raman Safety must be considered

How do we start solving problems? The raman spectroscopist working kit Calibration: the importance of the Calibration target – Exomars: 1 sample – Supercam: 25 samples Second Item in your kit: Acetaminophen

Instrument function, artifacts and other pains – Calibration lamp – NIST SRM – Just get your own refence… we did Third item in your kit: Reference material for intensity

Fluorescence Excited electronic states fluorescence emission Approach 1: move from VIS Raman spectroscopy Approach 2: Photobleaching Approach 3: Time resolved Raman

Enviroment Ambient light Cosmic rays Background due to the enviroment  dark scans Fourth item in your kit: hat, cap, jacket…

“Contact” Raman devices for Mars exploration

Raman Laser Spectrometer The (RLS) has been designed under a modularity concept: three units connected by means of electrical and optical harness. This configuration provides flexibility for being accommodated.

Raman Laser Spectrometer

Main instrument characteristics  It weighs ~ 2.3 kg.  Laser excitation wavelength: 532 nm  Irradiance on sample: 0.6 – 1.2 kW/cm 2  Spectral range: cm-1  Spectral resolution: 6 cm-1 lower spectral wavenumbers; 8 cm-1 long spectral wavenumbers  Spot size: 50 microns Science capabilities within Raman Shift range of cm-1

JPL

Remote Raman

General view of the Remote Raman Short distances: Micro-Raman Long distances: Remote-Raman

Remote Raman Inconvenients Figure from Wikipedia 5 mm 4  5·10 -3 ) 2 5 m 4  · Main difficulty: inverse square law Special requiremets

Changes in the equipment GATED CCD Spectrometer + Raman probe Increase light collection - Telescope Increase Raman emission - Pulsed Laser Improve the detection - Gated CCD Synchronism -Pulse 8ns -Delay (30 ns)

It’s worthy given the advantages Ambient light is not an incovenient Easy to combine with other techniques: LIBS, LIDAR, … No need of contact: Hostile enviroments, Simplify rover operations

Our setup

Operation 1/3 second Ambient light sec sec 0.01 sec 0.1 sec 300 accumulations

Sample preparation Identification of pure substances

Lysine: sec. and 300 accumulations

Pure substances (vials) Without a gated CCD With “small” collection optics High Repetition rate We could perform the identification of the Selected biomarkers at a distance of 5 meters.

What if we include a mineralogical context? Cysteine and Glycine: dried a solution of both substances at 50ºC on a basalt. Apocarotenal: mixture of water and propanol at room temperature. Dolomite

Less ammount of substance, less penetration of the laser, less emmiters. Contribution of the substrate Higger ammount of Raman emmiters thanks to the penetration of the laser

Glycine

Postprocessed: Noise reduction filter, baseline correction

Cysteine S-H st. ~ 2550 cm -1 S-S st. ~ 500 cm -1

Even with low quality spectra we could identify both substances over a mineralogical substrate The spectra are good enough to discover changes in one of the substances induced by the experiment. Those changes were confirmed with later experiments, FT-Raman, … Basalt Glass slide (same conditions)

Carotenoids Apocarotenal - Dolomite Remote spectra of apocarotenal over dolomite (red) and apocarotenal solution in a glass vial (blue)

Living colony of hematococcus pluvialis This alga produces a carotenoid called astaxanthin for UV protection

Remote raman FT- Raman

MARS 2020

Based onMSL Crédit: NASA/JPL-Caltech/Malin Space Science Systems (2012)

Distances of operation of Supercam SuperCam proposal for Mars 2020.

Synergies between techniques