The IR FEL at the Fritz Haber Institute Berlin: A Tool for IR Spectroscopy of Molecules, Clusters, and Solids

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1 The IR FEL at the Fritz Haber Institute Berlin: A Tool for IR Spectroscopy of Molecules, Clusters, and Solids Wieland Schöllkopf Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin

2 Outline 1. Design and specs of FHI FEL 2. Characterization of IR output Selected results from user experiments Possible future upgrades of FHI FEL

3 Interaction of molecules with IR light Far IR : large amplitude motion / folding metal-metal stretch van der Waals modes adsorbate modes on surfaces C=O Stretch: Amide I in biomolecules C=O on surfaces Fingerprint: skeletal motion in molecules X-H Stretch: H-bonding conformation of small biomolecules

4 Schematic layout of FHI FEL Mid-IR: 4 50 µm Far-IR: µm Linac MeV W. Schöllkopf et al., Proc. of SPIE Vol. 9512, 95121L (2015) Linac and electron beamline made by Advanced Energy Systems Inc., NY, USA

5 Linac specs summary Normal-conducting S-band accelerator: electron energy: RF frequency: bunch rep. rate: bunch charge: bunch length: macro-bunch length: macro-bunch rep. rate: Macro-bunch temporal structure MeV 3 GHz 1 GHz > 200 pc 1-5 ps 8 µs / 15 µs 10 Hz (typical) (18, 26, 38, 42 MeV) (220 pc) (10 µs) (5 Hz)

6 Specs of FHI FEL Mid-IR: IR wavelength: installed and commissioned Far-IR: projected IR cavity length: IR waveguide: ~3.5 ~50 µm 5.4 m none Undulator: planar hybrid, NdFeB period: number of periods: length: rms-k: IR cavity length: IR wavelength: IR waveguide: 40 mm 50 2m m ~30 ~500 µm 1-dim. 10 mm height Undulator: planar PPM or hybrid, SmCo or NdFeB period: 110 mm number of periods: 40 length: 4.4 m rms-k: 1 3

7 Specs of FHI FEL Time structure of IR output given by electrons: micro-pulses and macro-pulses IR output: macro-pulse length up to > 10 µs 100 mj / macro-pulse µj / micro-pulse micro-pulse length 0.3 >5 ps FT-limited bandwidth: 0.3 5% of central frequency

8 Photograph of FHI FEL IR mirror 2 Linac 2 Linac 1 Undulator Dump IR mirror 1

9 Time Structure of FEL Pulses Macro-pulses: Bursts of micropulses at 1 ns separation Fast MCT detector Vigo PEM-10.6 and 4 GHz oscilloscope

10 Time Structure of FEL Pulses Macro-pulses: Bursts of micropulses at 1 ns separation Fast MCT detector Vigo PEM-10.6 and 4 GHz oscilloscope

11 Macro-pulse energies at narrow bandwidth ( %) at 3.3 to 47 µm Wavelength (micron) Electron energy Wavenumber (1/cm)

12 FHI FEL Spectrum Line spectrum measured with a grating spectrometer (Acton, 75 g / mm) FEL spectrum Typically % FWHM for IR spectroscopic experiments

13 Outline 1. Design and specs of FHI FEL 2. Characterization of IR output Selected results from user experiments Possible future upgrades of FHI FEL

14 FHI FEL IR-Beamline Stations 1. André Fielicke (FHI, TU Berlin): Chemistry of transition metal clusters 2. Knut Asmis (FHI, U Leipzig): Vibrational spectroscopy of gas-phase metal-oxide clusters 3. Knut Asmis (FHI, U Leipzig): Vibrational spectroscopy of gas-phase clusters: ion solvation 4. Gert von Helden (FHI): Bio-molecules embedded in superfluid helium nano-droplets 5. Gert von Helden (FHI): Bio-molecules: IR spectroscopy combined with ion mobility spectrometry 6. Alexander Paarmann (FHI): Nonlinear spectroscopy of solids Starting spring 2015: Helmut Kuhlenbeck (FHI): Vibrational spectroscopy of surface-deposited clusters

15 IR Spectroscopy of Aluminum Oxide Clusters Experimental Blue-Al Red-O K. Asmis, M. Fagiani, X. Song, N. Heine, T. Esser, H. Knorke Theory: F. Bischoff, J. Sauer, HU Berlin Theoretical Experimental Experimental Theoretical Theoretical

16 IR spectroscopy of bio-molecules Structural analysis of molecules in the gas phase by IR multiple photon dissociation (IR-MPD) Benzocaine Commonly used local anesthetic IR Spectroscopy of protonated Benzocaine Different sites for proton attachment: protomers

17 IR spectroscopy of bio-molecules Ion mobility Expt. FEL N-protonated Theory O-protonated S. Warnke et al. Protomers of Benzocaine: Solvent and Permittivity Dependence, J. Am. Chem. Soc., 137, 4236 (2015).

18 Nonlinear IR-Spectroscopy of Solids Second harmonic generation (SHG) spectroscopy Spectral peaks near TO and LO phonon modes (Reststrahlen band) Group of Alex Paarmann (FHI Berlin) TO phonon ~12 µm A. Paarmann et al., Appl. Phys. Lett. 107, (2015) LO phonon ~10 µm

19 Outline 1. Design and specs of FHI FEL 2. Characterization of IR output Selected results from user experiments Possible future upgrades of FHI FEL

20 Outlook II Possible FHI FEL upgrade; FIR/THz Undulator projected Far-IR: IR wavelength: ~30 ~500 µm IR cavity length: 7.2 m IR waveguide: 1-dim. 10 mm height (?) Undulator: PPM or hybrid period: 110 mm number of periods: 40 length: 4.4 m rms-k: 1 3

21 Outlook III Idea for 2-color FEL Possible applications: IR pump-probe experiments: MIR/MIR and MIR/FIR 2-d IR spectroscopy Sum frequency generation