Single Shot Measurement of Ultra-high Peak Intensities A. Link 1, E. A. Chowdhury 1, D. Offermann 1, L. Van Woerkom 1, R. R. Freeman 1, J. Pasley 2, F. N. Beg 2, P. Rambo 3, J. Schwarz 3, M. Geissel 3, E. Brambrink 3, A. D. Edens 3, B. W. Atherton 3 and J. L. Porter 3 1 The Ohio State University 2 The University of California, San Diego 3 Sandia National Laboratories Theory: Tunneling ionization - Single shot intensity calibration of focused laser is possible - Semi-classical tunneling ionization 3 experimentally verified - up to W/cm 2 by Chowdhury et. al. 4 - since the probability of tunnel ionization ~ I 5 below saturation - highest peak intensity is confined to very small focal volume - Lower and upper bound for the peak focal intensity - Single shot detection of a high charge state (saturation) - non-detection of the next high charge state (non-saturation) - requires high ion detection efficiency and spatial filtering. Above: A Cartoon representation of tunneling ionization (actual barrier is 3D). Right: Constant intensity surfaces of a focused Gaussian beam at intensities of 1/2, 1/4, 1/8, 1/16, and 1/e 2 of the maximum intensity. Higher intensities are confined to smaller volumes and measuring the highest ionization states is an accurate indication of the peak intensity of the focused beam. Experimentally measured intensity dependence of ionization yield for Ne 5+ (diamond), Ne 6+ (filled circle), Ne 7+ (square), and Ne 8+ (filled triangle). The calculated tunneling ionization yield curves are also shown for Ne 5+ (dotted curve), Ne 6+ (dotted–dashed curve), Ne 7+ (solid curve), and for Ne 8+ (short–dashed curve) 5 (a)Plot of Semi-classical ionization yields at intensities 0.7 × W/cm 2, 0.8×10 19 W/cm 2,1x10 19 W/cm 2,and 2 x10 19 W/cm 2, represented by open diamonds, solid triangles, crosses and open circles, respectively. Experimental data points at an intensity of 2 × W/cm 2 are shown as solid squares. (b)Plot of experimental (  ) ion yields at an intensity of 2×10 19 W/cm 2 and best fit calculated ionization yields scaled to the experimental yield (  ) at 0.8×10 19 W/cm 2. The yields have been normalized relative to the experimental yield of Ar9+. 3 References 1.R. R. Freeman, D. Batani, S. Baton, M. Key, R. Stephens, Fusion Science and Technology, 49, 297 (2006). 2.A. Link, E. Chowdhury, et. al. Rev. Sci. Inst. 77, 10E723 (2006). 3.B. M. Smirnov and M. I. Chibisov, Zh. Eksp. Teor. Fiz. 49, p. 841, 1965 [Sov. Phys. JETP 22, p. 585, 1966]; A. M. Perelomov, V. S. Popov, and M. V. Terent’ev, Zh. Eksp. Teor. Fiz. 50, p. 1393, 1966 [Sov. Phys. JETP 23, p ]. 4.E. Chowdhury, C. P. J. Barty, B. C. Walker, Phys. Rev. A, 63, (2001). 5.E. Chowdhury, PhD Thesis, University of Delaware (2004). -TOF tube aligned & calibrated using 2 mJ 10 Hz OPCPA beam - Various levels of amplification used to ionize Ar and Ne w/ base/target pressure of 1 × torr/5 × torr - As energy increases SNR decreases due to increasing space charge & degradation of the focal spot quality - Despite decrease in SNR, still possible to distinguish peaks and calculate m/q - With known amounts of background gases, one can label each ion available in the spectra - Shots at each energy consistent with each other  average several shots to increase the SNR mJ level it is possible to see up to Ar 7+  intensity estimated to be 1 × W/cm 2 - Ne 8+ at 1.7 J  2 × W/cm 2 (Ne 8+ ) for 1.7 J/pulse - Ar 12+ at 15-16J  2 × W/cm 2 for 16 J/pulse - Indirect measurements - ~3 ps pulse duration & ~20 micron diameter focal spot  peak intensity at 16 J is 1.6 × W/cm 2 - agrees well with experimental data. It can be done!! Calculated intensity dependent volume integrated tunnel ionization yield curves for L-shell argon charge states Calculated intensity dependent tunnel ionization probability curves for L-shell neon charge states Cartoon contrasting ‘real’ and ‘ideal’ pulses 2 Laser Intensity dependent hot electron coupling efficiency. 1 Motivation Peak focal Intensity a crucial parameter in Fast Ignition Fusion But estimated via difficult indirect measurements… Not measured 2 mJ 2 J 2 J w AO 20 J Non-ideal focus Not fully amplified Pulse duration measurement Leakage through dispersive medium Un-amplified beams Low dynamic range Significant pulse Energy may reside in the pedestal Actual Intensity  Estimated Intensity!!! - Ion products collected by a time of flight (TOF) detector - Sample gas atoms supplied via an effusive jet and a skimmer - Apparatus  acceleration plates, drift tube, ion selector & MCP - Laser focus between plates 2 and 3 ( kV ) - quick extraction & limits space charge effects on signal. - Additional acceleration region between plates 3 and 4 - provides spatio-temporal lensing & improves collection efficiency - Final plate  limits collected ions to the regions of high intensity - Ion selector in field free drift tube blocks copious ions of large m/q The Apparatus Front End (General Atomics) Nd:glass rod-amps Beamlet slab-amps sub-aperture Beamlet slab-amps full aperture Probe Beam 10TW PW 100TW Z-PetaWatt Laser System Pulse energies up to 18 J/shot compressed have been used in these experiments Single Shot Intensity Calibration: Challenges Typical Field ionization experiments require base pressure torr Low event probability/time bin 10 4 – 10 8 laser shots Energy/pulse – 1 J Small dedicated chamber: detector solid angle relatively large Typical Petawatt facility like Sandia ZPW have Base pressure torr High event probability Single Shot Energy/pulse 1 – 10 2 J Large target chamber: detector solid angle small Experimental Confirmation