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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 Slide 2 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 Slide 3 1. Ultrafast Dynamics in Intense Fields www.ultrafastbelfast.co.uk Dr. Jason Greenwood Prof. Ian Williams Dr. Chris Calvert Orla Kelly Raymond King Leigh Graham Martin Duffy Louise Belshaw Slide 4 Ultrafast Pump(10fs)-probe(10fs) Scheme Theoretical and Experimental Studies of Nuclear Wavepackets in H 2 + Slide 5 Europhysics News Highlight: 41/2 (2010) Control Slide 6 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 Slide 7 2. Linear Electrostatic Ion Trap Field Free Region Focusing Region Reflecting Region Weizmann Trap Dahan et al., Rev. Sci. Instrum., 69, 76 (1997) Slide 8 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 Slide 9 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 ? Slide 10 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 Slide 11 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 Slide 12 Image Charge Signal H 2 O + Centre Pickup Offset Pickup Slide 13 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 Slide 14 Mass Separation Capability Isotopes of Xenon Slide 15 Mass Separation 180 oscillations 600 oscillations 6000 oscillations 5 km Slide 16 4. Fourier Analysis Centre Pickup - Fast Fourier Transform (FFT) H 2 O + Offset Pickup - FFT Slide 17 Time Signal twtw t T T/4 Slide 18 Fourier Transform f ~ f 2/ T FT Slide 19 Mass Resolution Ion velocity Oscillation Frequency Mass Resolution If f constant, R increases linearly with harmonic order Slide 20 2 nd harmonic R = 2600 20 th harmonic R = 20000 136 Xe + 134 Xe + 132 Xe + 131 Xe + 130 Xe + 128 Xe + 129 Xe + Fast Fourier Transform Xe Data Slide 21 Fourier Transform best for Our Signal? Harmonics make it hard to convert frequency to mass spectrum Better resolution possible? Slide 22 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? Slide 23 A Comb Function? Slide 24 Slide 25 Slide 26 Slide 27 Slide 28 Slide 29 Slide 30 Measuring the Frequency of a Comb t 0 1/f 0 Slide 31 Measuring the Frequency of a Comb t 0 1/f 0 Slide 32 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 Slide 33 Comb Sampling Spectrum of Perfect Comb Data A = B = - 1 / 28 (AB) 1/2 Slide 34 Comb Sampling Spectrum of Simulated Data A = C = - 0.06 B = - 1 / 28 Slide 35 (AB) 1/2 (ABC) 1/3 Comb Sampling Spectrum of Simulated Data Combined Spectra Slide 36 Comb Sampling Spectrum of Real Data vs FFT FFT Comb (2 pickup signals combined) Xe isotopes Slide 37 Advantages Over Fourier Transform Single harmonic per ion with high frequency precision Xe ions trapped for 100 ms FFT resolution 2600 Comb resolution 25000 Resolution currently limited by Ion lifetime (background gas pressure) Power supply stability Slide 38 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 Slide 39 Advantages Over Fourier Transform FFT Comb Electronic Noise Slide 40 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 Slide 41 Fourier Windowing Some windows and their Fourier response Rectangle Blackman Spectral leakage Slide 42 Comb Windowing No spectral leakage Better ion bunch separation at later times. Can weight asymmetrically Slide 43 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 Slide 44 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) Slide 45 2+ 1+ C2Hn+C2Hn+ CH n + C3Hn+C3Hn+ H2O+H2O+ Allene C 3 H 4 800 nm, Intensity 2 10 14 Wcm -2 1 st ionization potential 9.6 eV 2 nd ionisation potential 25.6 eV 150 fs Slide 46 2+ 1+ 105 fs Slide 47 2+ 1+ 71 fs Slide 48 2+ 1+ 37 fs Slide 49 2+ 1+ 15 fs Slide 50 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 Slide 51 Electron Impact Ionisation 70 eV Slide 52 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, 1300-1600 nm Butadiene Slide 53 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) http://spie.org/x41567.xml?ArticleID=x41567 Gas phase biomolecules attained via Slide 54 For example: Observation of Electron Wavepackets Photosynthesis The quantum life Physics World, July 2009 YC Cheng & GR Fleming 2009 Ann Rev Phys Chem 60 241 Future Directions: Ultrafast processes in Complex Molecules Peptide Trp(Leu) 3 from Remacle and Levine, PNAS, 103, 6793 (2006) Slide 55 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 Slide 56 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 Slide 57 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