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CHIMERA: Can we do better than Fourier in analysing signal from a novel electrostatic ion trap mass spectrometer? Jason Greenwood Centre for Plasma Physics

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1. Ultrafast Dynamics Group 2. Linear Electrostatic Ion Trap 3. Application to Mass Spectrometry 4. Frequency Analysis: Comb Function vs 5. Results / Future Directions Outline

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1. Ultrafast Dynamics in Intense Fields Dr. Jason Greenwood Prof. Ian Williams Dr. Chris Calvert Orla Kelly Raymond King Leigh Graham Martin Duffy Louise Belshaw

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Ultrafast Pump(10fs)-probe(10fs) Scheme Theoretical and Experimental Studies of Nuclear Wavepackets in H 2 +

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Europhysics News Highlight: 41/2 (2010) Control

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1. Source 2. m/q Analysing Magnet CEM 3. Trapping and Interaction Region fs Laser D 3 +, HD + Trapping to radiatively cool molecules Dissociation of Fundamental Molecular Ions Linear Electrostatic Ion Beam Trap

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2. Linear Electrostatic Ion Trap Field Free Region Focusing Region Reflecting Region “Weizmann Trap” – Dahan et al., Rev. Sci. Instrum., 69, 76 (1997)

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Ion Trapping Ion bunches injected from ECR ion source 200 nA beam of 1 keV HD + ions Initial ion bunch injection 3 x 10 6 ions to CEM neutralisation

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Advantages of Linear Electrostatic traps Compact alternative to large storage ring – Ions have beamlike properties – Long field-free region Ion bunches monitored by non-destructive pickup detector High resolution mass spectrometry possible Static Potentials – Trapping dependent on E/q only – Mass independent trapping! H 2 O – 18u Butadiene – 54u Cyanohydroxycinnamic acid – 189u Proteins ?

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Einzel Lens Electrostatic Mirror Field Free Drift Region POTENTIAL ENERGY SURFACE Image Charge Detection Einzel Lens Electrostatic Mirror KILOVOLT ELECTROSTATIC ION REFLECTION ANALYSER (KEIRA) Electrostatic storage device for mass spectrometry of femtosecond laser produced ions 3. Application to Mass Spectrometry

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pick-up signal time smaller m/q m 1 larger m/q m 2 t1t1 t2t2 fs laser KEIRA electrostatic trapping region Gas Period of oscillation ~ (m/q) 1/2 Electrostatic Ion Trap as a Mass Spectrometer

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Image Charge Signal – H 2 O + Centre Pickup Offset Pickup

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Ion Loss and Diffusion Loss Mechanisms Unstable Trajectories Elastic and Inelastic collisions with background gas Bunch Elongation – differences in oscillation times Trajectories Energy differences 30 oscillations 150 oscillations750 oscillations

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Mass Separation Capability Isotopes of Xenon

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Mass Separation 180 oscillations 600 oscillations 6000 oscillations 5 km

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4. Fourier Analysis Centre Pickup - Fast Fourier Transform (FFT) H 2 O + Offset Pickup - FFT

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Time Signal twtw t T T/4

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Fourier Transform f ~ f 2/ T FT

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Mass Resolution Ion velocity Oscillation Frequency Mass Resolution If f constant, R increases linearly with harmonic order

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2 nd harmonic R = th harmonic R = Xe Xe Xe Xe Xe Xe Xe + Fast Fourier Transform Xe Data

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Fourier Transform best for Our Signal? Harmonics make it hard to convert frequency to mass spectrum Better resolution possible?

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Fourier Analysis - sinusoids Non-local Poorly describes discontinuities Wavelet Analysis Local Wavelet functions Gives time-frequency (delay – scale) information Try Mexican hat wavelet – a better match to our signal? Yes, but gives temporal rather than frequency information. Uncertainty means temporal resolution reduces frequency precision A Wavelet Transform?

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A Comb Function?

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Measuring the Frequency of a Comb t 0 1/f 0

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Measuring the Frequency of a Comb t 0 1/f 0

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Offset Comb t 0 /f0 /f0 S ( f ) significant only if recurring m, n values satisfy If is irrational, no harmonics, i.e. contributions only when m=n

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Comb Sampling Spectrum of “Perfect Comb” Data A = ¼ B = ¼ - 1 / 28 (AB) 1/2

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Comb Sampling Spectrum of Simulated Data A = ¼ C = ¼ B = ¼ - 1 / 28

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(AB) 1/2 (ABC) 1/3 Comb Sampling Spectrum of Simulated Data Combined Spectra

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Comb Sampling Spectrum of Real Data vs FFT FFT Comb (2 pickup signals combined) Xe isotopes

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Advantages Over Fourier Transform Single harmonic per ion with high frequency precision Xe ions trapped for 100 ms FFT resolution 2600 Comb resolution Resolution currently limited by Ion lifetime (background gas pressure) Power supply stability

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Advantages Over Fourier Transform Single harmonic per ion with high frequency precision Direct conversion to mass spectrum possible Phase information ultilised. Uncorrelated electronic noise suppressed FFT Comb

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Advantages Over Fourier Transform FFT Comb Electronic Noise

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Advantages Over Fourier Transform Single harmonic per ion with high frequency precision Direct conversion to mass spectrum possible Phase information ultilised. Uncorrelated electronic noise suppressed No limitations on data windowing

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Fourier Windowing Some windows and their Fourier response Rectangle Blackman Spectral “leakage”

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Comb Windowing No spectral leakage Better ion bunch separation at later times. Can weight asymmetrically

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Optimum Conditions for Comb Sampling Narrower impulses yield Fewer fractional harmonics Higher frequency precision Well defined phase/offset Oscillation period ( 1/f 0 ) proportional to initial time offset ( /f 0 ) is constant for electrostatic ion optics Offset - ideally avoids well factorised fractional values Multiple acquisition signals with different offsets enhance Spectral purity Signal to noise

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5. Future Applications in Mass Spectrometry Generation of intact molecular ions using fs lasers Very high ionisation efficiency Low fragmentation? (Conventional electron impact ionisation - 70 eV)

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2+ 1+ C2Hn+C2Hn+ CH n + C3Hn+C3Hn+ H2O+H2O+ Allene C 3 H nm, Intensity 2 Wcm -2 1 st ionization potential 9.6 eV 2 nd ionisation potential 25.6 eV 150 fs

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fs

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fs

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fs

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fs

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Shortening pulse length closes excitation channels as molecule becomes “frozen” reduces dissociation, 2+ production Increased intensity More fragmentation Increases time molecule exposed to fixed intensity

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Electron Impact Ionisation 70 eV

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Shortening pulse length closes excitation channels as molecule becomes “frozen” reduces dissociation, 2+ production Increased intensity More fragmentation Increases time molecule exposed to fixed intensity Currently Studying Wavelength dependence, 400 nm, nm Butadiene

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Future Applications in Mass Spectrometry Generation of intact molecular ions using fs lasers Very high ionisation efficiency Low fragmentation under appropriate pulse parameters (Conventional electron impact ionisation - 70 eV) Biopolymer sequencing (e.g. proteins) Gas phase biomolecules attained via

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For example: Observation of Electron Wavepackets Photosynthesis The quantum life Physics World, July 2009 YC Cheng & GR Fleming 2009 Ann Rev Phys Chem Future Directions: Ultrafast processes in Complex Molecules Peptide Trp(Leu) 3 from Remacle and Levine, PNAS, 103, 6793 (2006)

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Summary Novel Electrostatic Ion Trap Mass Spectrometer (KEIRA) Very high resolution possible Trapping mass independent Detection mass independent, non-destructive Fs laser generates ions in-situ fs laser interactions with organic molecule Parent ion production dominates as intensity, pulse length reduced Applications in mass spectrometry, e.g. complex mixture of chemicals Comb Sampling Frequency Analysis High Resolution “Pure” spectrum Reduction in electronic noise Utilises multiple detection signals

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Are we doing better than Joseph Fourier with CHIMERA? CHIMERA has also come to mean, an impossible or foolish fantasy, hard to believe CHIMERA Comb-sampling for High-resolution IMpulse-train frequency ExtRAction

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Acknowledgements Ian Williams John Alexander Ray King Chris Calvert Orla Kelly Martin Duffy Louise Belshaw Leigh Graham Emma Springate Edmond Turcu Cephise Cacho Will Bryan

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