Bright Attosecond Pulse Generation

Photograph of a typical experimental setup at the JETI40 laser system
Photograph of a typical experimental setup at the JETI40 laser system
Close up of a shot glass target surface which must be moved after each shot to provide a fresh surface
Close up of a shot glass target surface which must be moved after each shot to provide a fresh surface
Experimentally observed ROM spectrum from JETI40 laser with frequency on the vertical axis and angle of emission on the horizontal.
Here, clear beamed XUV emission is observed up the 30th harmonic (27nm or 47eV).
Experimentally observed ROM spectrum from JETI40 laser with frequency on the vertical axis and angle of emission on the horizontal. Here, clear beamed XUV emission is observed up the 30th harmonic (27nm or 47eV).
(a) Upshift due to reflection from a mirror moving with a constant velocity, v, as predicted by Special Relativity.  
(b) Mirror surface with an effective reflection point X(t) which oscillates with the laser frequency. (a) Upshift due to reflection from a mirror moving with a constant velocity, v, as predicted by Special Relativity. (b) Mirror surface with an effective reflection point X(t) which oscillates with the laser frequency.

Intense Laser Driven Plasma Surfaces:
 
During the interaction of an ultra-intense laser pulse (>1018Wcm-2) with a solid surface, electrons in the target material’s atoms are ripped away, resulting in an ionised plasma. The electric field of the incident laser is then able to enact extreme forces on this newly formed flat plasma surface, accelerating electrons in it to velocities approaching the speed of light. In a remarkable demonstration of the Doppler effect – the shift in frequency of radiation due to the motion of its source – the laser light reflected back from this surface is heavily upshifted to very high frequencies in the extreme ultraviolet (wavelengths of 10nm to 100nm) or even X-ray (<10nm) regions of the electromagnetic spectrum. In our everyday experience we are familiar with this effect when hearing the change in pitch of a siren from a passing vehicle but the equivalent effect for light waves is properly described by application of Einstein’s Special Relativity. The regular observations of this upshifted light in laboratory experiments serves as a surprising demonstration of this important theory.
 

The Relativistically Oscillating Mirror:

As the electric field of the laser is cyclical, this upshift process happens periodically at the frequency of the laser light which is typically in the visible or infrared. This results in a series of ultrashort sub-cycle duration XUV bursts emitted in a pulse train which interfere in the spectral domain and manifest themselves as harmonics of the laser frequency. This is analogous to the diffraction of monochromatic light at a set of evenly spaced slits which forms an interference pattern on a distant screen with the spacing of the maxima depending on the distance between the slits. The harmonics that appear in the experimentally observed spectra are a remarkable demonstration of a coherent and ordered process emerging from the complex and extreme environment of a relativistic plasma. Furthermore, the spatial coherence of the driving laser is also imprinted on the generated radiation, leading to a directed beam of XUV light which can be transported and refocussed elsewhere. The manner in which these harmonics are generated, through upshifting of the reflected radiation, means that for many purposes, the plasma surface can be described as a Relativistically Oscillating Mirror (ROM). This model is a useful macroscopic view of the generation mechanism and provides some important insights into how the properties of the reflected radiation behave.

A Source of Attosecond XUV Radiation:

The resulting radiation has potential applications as a small scale laser based source of coherent ultra-bright XUV as compared to alternative accelerator sources such as synchrotrons or free electron lasers which require massive infrastructure. The unique aspect of the ROM radiation is, however, that it contains very short, attosecond (10-18s) scale pulses. This is the temporal scale of electron orbits in atoms and molecules. With access to light pulses of this duration, we effectively have an ultrashort flash that can be used to take snapshots of the dynamics of such systems.

Our Role:

Here at the CPP, in collaboration with groups across the globe, researchers are engaged at the forefront of research into this source. Our work takes places at several different internationally recognised laser facilities including:

The Trident Laser Facility at Los Alamos National Laboratories in the USA
http://www.lanl.gov/science-innovation/science-facilities/trident-laser-facility/

The twin laser beams of the Astra Gemini facility based at the Central Laser Facility in the UK
http://www.clf.stfc.ac.uk/Facilities/Astra/Astra+Gemini/12258.aspx

The JETI40 and JETI200 lasers based at the Helmholtz Institute Jena in Germany
https://www.hi-jena.de/en/helmholtz_institute_jena/experimental_facilities/local/jeti40-laser/
https://www.hi-jena.de/de/helmholtz_institute_jena/experimental_facilities/local/jeti200-laser/

Additionally, it is expected that the new TARANIS-X laser upgrade, by virtue of its unique combination of high energy and few cycle pulse duration, will provide exciting new opportunities to explore the attosecond properties of this source by allowing the gating of the process to only a single, isolated attosecond pulse.
http://www.qub.ac.uk/research-centres/CentreforPlasmaPhysics/ProjectsFacilities/TARANIS-X/

Our current research aims are constantly evolving and include:

⦁ Isolating individual attosecond pulses from the pulse train
⦁ Developing novel techniques for characterisation of the attosecond pulse duration
⦁ Optimising the XUV yield from the interaction using laser pulses of multiple frequencies
⦁ Pushing towards higher photon energies in the soft X-ray regime
⦁ Investigating the effects of different plasma density profiles
⦁ Simulating the interaction using the particle-in-cell (PIC) method which is ideal for modelling relativistic plasmas

Review Articles:

⦁ C. Thaury and F. Quéré, “High-order harmonic and attosecond pulse generation on plasma mirrors: basic mechanisms”, J Phys. B: At. Mol. Opt. Phys. 43 213001 (2010)

⦁ U. Teubner and P. Gibbon, “High-order harmonics from laser-irradiated plasma surfaces”, Rev. Mod. Phys. 81 445 (2009)

Recent CPP papers:

⦁ M. Yeung, J. Bierbach, E. Eckner, S. Rykovanov, S. Kuschel, A. Sävert, M. Förster, C. Rödel, G. G. Paulus, S. Cousens, M. Coughlan, B. Dromey and M. Zepf, “Noncollinear Polarization Gating of Attosecond Pulse Trains in the Relativistic Regime”, Phys. Rev. Lett. 115 193903 (2015)
⦁ J. Bierbach, M. Yeung, E. Eckner, C. Roedel, S. Kuschel, M. Zepf, and G. G. Paulus, “Long-term operation of relativistic surface high-harmonic generation using a spooling tape”, Opt. Express, 23 12321 (2015)
⦁ T. Hahn, J. Bierbach, C. Rödel, D. Hemmers, M. Yeung, B. Dromey, S. Fuchs, A. Galestian, S. Kuschel, M. Zepf, G. G. Paulus and G. Pretzler, “Broadband XUV polarimetry of high harmonics from plasma surfaces using multiple Fresnel reflections“, Appl. Phys. B 118 241 (2015)
⦁ M. Yeung, B. Dromey, S. Cousens, T. Dzelzainis, D. Kiefer, J. Schreiber, J. H. Bin, W. Ma, C. Kreuzer, J. Meyer-ter-Vehn, M. J. V. Streeter, P. S. Foster, S. Rykovanov and M. Zepf, “Dependence of Laser-Driven Coherent Synchrotron Emission Efficiency on Pulse Ellipticity and Implications for Polarization Gating“, Phys. Rev. Lett. 112 123902 (2014)
⦁ W. J. Ma, J. H. Bin, H. Y. Wang, M. Yeung, C. Kreuzer, M. Streeter, P. S. Foster, S. Cousens, D. Kiefer, B. Dromey, X. Q. Yan, J. Meyer-ter-Vehn, M. Zepf, and J. Schreiber, “Bright Subcycle Extreme Ultraviolet Bursts from a Single Dense Relativistic Electron Sheet”, Phys. Rev. Lett. 113 235002 (2014)
⦁ M. Yeung, B. Dromey, D. Adams, S. Cousens, R. Hörlein, Y. Nomura, G. D. Tsakiris, and M. Zepf, “Beaming of High Order Harmonics Generated from Laser-Plasma Interactions”, Phys. Rev. Lett. 110 165002 (2013)
⦁ D. Kiefer, M. Yeung, T. Dzelzainis, P.S. Foster, S.G. Rykovanov, C.L.S. Lewis, R.S. Marjoribanks, H. Ruhl, D. Habs, J. Schreiber, M. Zepf and B. Dromey, “ Relativistic electron mirrors from nanoscale foils for coherent frequency upshift to the extreme ultraviolet”, Nat. Commun. 4 1763 (2013)
⦁ B. Dromey, S. Cousens, S. Rykovanov, M. Yeung, D. Jung, D. C. Gautier, T. Dzelzainis, D. Kiefer, S. Palaniyppan, R. Shah, J. Schreiber, J. C. Fernandez, C. L. S. Lewis, M. Zepf, and B. M. Hegelich, “Coherent synchrotron emission from dense electron nanobunches in relativistic laser plasmas”, New J. Phys. 15 015025 (2013)
⦁ S. Kahaly, S. Monchocé, H. Vincenti, T. Dzelzainis, B. Dromey, M. Zepf, Ph. Martin, and F. Quéré, “Direct Observation of Density-Gradient Effects in Harmonic Generation from Plasma Mirrors”, Phys. Rev. Lett. 110 175001 (2013)
⦁ B. Dromey, S. Rykovanov, M. Yeung, R. Hörlein, D. Jung, D. C. Gautier, T. Dzelzainis, D. Kiefer, S. Palaniyppan, R. Shah, J. Schreiber, H. Ruhl, J. C. Fernandez, C. L. S. Lewis, M. Zepf and B. M. Hegelich, “Coherent synchrotron emission from electron nanobunches formed in relativistic laser–plasma interactions”, Nat. Phys. 8 804 (2012)
⦁ C. Rödel, D. an der Brügge, J. Bierbach, M. Yeung, T. Hahn, B. Dromey, S. Herzer, S. Fuchs, A. Galestian Pour, E. Eckner, M. Behmke, M. Cerchez, O. Jäckel, D. Hemmers, T. Toncian, M. C. Kaluza, A. Belyanin, G. Pretzler, O. Willi, A. Pukhov, M. Zepf, and G. G. Paulus, “Harmonic Generation from Relativistic Plasma Surfaces in Ultrasteep Plasma Density Gradients”, Phys. Rev. Lett. 109 125002 (2012)
⦁ J. Bierbach, C. Rödel, M. Yeung, B. Dromey, T. Hahn, A. Galestian Pour, S. Fuchs, A. E. Paz, S. Herzer, S. Kuschel, O Jäckel, M. C. Kaluza, G. Pretzler, M. Zepf and G. G. Paulus, “Generation of 10μW relativistic surface high-harmonic radiation at a repetition rate of 10 Hz”, New J. Phys. 14 065005 (2012)
⦁ B. Dromey, D. Adams, R. Hörlein, Y. Nomura, S. G. Rykovanov, D. C. Carroll, P. S. Foster, S. Kar, K. Markey, P. McKenna, D. Neely, M. Geissler, G. D. Tsakiris and M. Zepf, “Diffraction-limited performance and focusing of high harmonics from relativistic plasmas”, Nat. Phys. 5 146 (2009)
⦁ B. Dromey, S. G. Rykovanov, D. Adams, R. Hörlein, Y. Nomura, D. C. Carroll, P. S. Foster, S. Kar, K. Markey, P. McKenna, D. Neely, M. Geissler, G. D. Tsakiris, and M. Zepf, “Tunable Enhancement of High Harmonic Emission from Laser Solid Interactions”, Phys. Rev. Lett. 102 225002 (2009)
⦁ Y. Nomura, R. Hörlein, P. Tzallas, B. Dromey, S. Rykovanov, Zs. Major, J. Osterhoff, S. Karsch, L. Veisz, M. Zepf, D. Charalambidis, F. Krausz and G. D. Tsakiris, “Attosecond phase locking of harmonics emitted from laser-produced plasmas”, Nat. Phys. 5 124 (2009)
⦁ M. Zepf, B. Dromey, S. Kar, C. Bellei, D. C. Carroll, R. J. Clarke, J. S. Green, S. Kneip, K. Markey, S. R. Nagel, P. T. Simpson, L. Willingale, P. McKenna, D. Neely, Z. Najmudin, K. Krushelnick and
P. A. Norreys, “High harmonics from relativistically oscillating plasma surfaces—a high brightness attosecond source at keV photon energies” Plasma Phys. Control Fusion 49 B149 (2007)
⦁ B. Dromey, S. Kar, C. Bellei, D. C. Carroll, R. J. Clarke, J. S. Green, S. Kneip, K. Markey, S. R. Nagel, P. T. Simpson, L. Willingale, P. McKenna, D. Neely, Z. Najmudin, K. Krushelnick, P. A. Norreys, and M. Zepf, “Bright Multi-keV Harmonic Generation from Relativistically Oscillating Plasma Surfaces” Phys. Rev. Lett. 99 085001 (2007)
⦁ B. Dromey, M. Zepf, A. Gopal, K. Lancaster, M. S. Wei, K. Krushelnick, M. Tatarakis, N. Vakakis, S. Moustaizis, R. Kodama, M. Tampo, C. Stoeckl, R. Clarke, H. Habara, D. Neely, S. Karsch and P. Norreys, “High harmonic generation in the relativistic limit”, Nat. Phys. 2 456 (2006)