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Abstract
Attoscience is the study of physical processes that occur in less than a fraction of a cycle of visible light, in times less than a quadrillionth of a second. The motion of electrons inside atoms and molecules that are undergoing photoionization or chemical change falls within this time scale, as does the plasma motion that causes the reflectivity of metals. The techniques to study motion on this scale are based on careful control of strong-field laser-atom interactions. These techniques and new research opportunities in attosecond spectroscopy are reviewed.
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Florean AC, Carroll EC, Spears KG, Sension RJ, Bucksbaum PH. Optical control of excited-state vibrational coherences of a molecule in solution: The influence of the excitation pulse spectrum and phase in LD690. J Phys Chem B 2007; 110:20023-31. [PMID: 17020390 DOI: 10.1021/jp0627628] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Spectral and phase shaping of femtosecond laser pulses is used to selectively excite vibrational wave packets on the ground (S0) and excited (S1) electronic states in the laser dye LD690. The transient absorption signals observed following excitation near the peak of the ground-state absorption spectrum are characterized by a dominant 586 cm(-1) vibrational mode. This vibration is assigned to a wave packet on the S0 potential energy surface. When the excitation pulse is tuned to the blue wing of the absorption spectrum, a lower frequency 568 cm(-1) vibration dominates the response. This lower frequency mode is assigned to a vibrational wave packet on the S1 electronic state. The spectrum and phase of the excitation pulse also influence both the dephasing of the vibrational wave packet and the amplitude profiles of the oscillations as a function of probe wavelength. Excitation by blue-tuned, positively chirped pulses slows the apparent dephasing of the vibrational coherences compared with a transform-limited pulse having the same spectrum. Blue-tuned negatively chirped excitation pulses suppress the observation of coherent oscillations in the ground state.
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53
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Carroll EC, Pearson BJ, Florean AC, Bucksbaum PH, Sension RJ. Spectral phase effects on nonlinear resonant photochemistry of 1,3-cyclohexadiene in solution. J Chem Phys 2007; 124:114506. [PMID: 16555900 DOI: 10.1063/1.2168454] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have investigated the ring opening of 1,3-cyclohexadiene to form 1,3,5-cis-hexatriene (Z-HT) using optical pulse shaping to enhance multiphoton excitation. A closed-loop learning algorithm was used to search for an optimal spectral phase function, with the effectiveness or fitness of each optical pulse assessed using the UV absorption spectrum. The learning algorithm was able to identify pulses that increased the formation of Z-HT by as much as a factor of 2 and to identify pulse shapes that decreased solvent fragmentation while leaving the formation of Z-HT essentially unaffected. The highest yields of Z-HT did not occur for the highest peak intensity laser pulses. Rather, negative quadratic phase was identified as an important control parameter in the formation of Z-HT.
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54
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Hillyard PB, Gaffney KJ, Lindenberg AM, Engemann S, Akre RA, Arthur J, Blome C, Bucksbaum PH, Cavalieri AL, Deb A, Falcone RW, Fritz DM, Fuoss PH, Hajdu J, Krejcik P, Larsson J, Lee SH, Meyer DA, Nelson AJ, Pahl R, Reis DA, Rudati J, Siddons DP, Sokolowski-Tinten K, von der Linde D, Hastings JB. Carrier-density-dependent lattice stability in InSb. PHYSICAL REVIEW LETTERS 2007; 98:125501. [PMID: 17501133 DOI: 10.1103/physrevlett.98.125501] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2006] [Indexed: 05/15/2023]
Abstract
The ultrafast decay of the x-ray diffraction intensity following laser excitation of an InSb crystal has been utilized to observe carrier dependent changes in the potential energy surface. For the first time, an abrupt carrier dependent onset for potential energy surface softening and the appearance of accelerated atomic disordering for a very high average carrier density have been observed. Inertial dynamics dominate the early stages of crystal disordering for a wide range of carrier densities between the onset of crystal softening and the appearance of accelerated atomic disordering.
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55
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Fritz DM, Reis DA, Adams B, Akre RA, Arthur J, Blome C, Bucksbaum PH, Cavalieri AL, Engemann S, Fahy S, Falcone RW, Fuoss PH, Gaffney KJ, George MJ, Hajdu J, Hertlein MP, Hillyard PB, Horn-von Hoegen M, Kammler M, Kaspar J, Kienberger R, Krejcik P, Lee SH, Lindenberg AM, McFarland B, Meyer D, Montagne T, Murray ED, Nelson AJ, Nicoul M, Pahl R, Rudati J, Schlarb H, Siddons DP, Sokolowski-Tinten K, Tschentscher T, von der Linde D, Hastings JB. Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays. Science 2007; 315:633-6. [PMID: 17272718 DOI: 10.1126/science.1135009] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid.
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Gaffney KJ, Lindenberg AM, Larsson J, Sokolowski-Tinten K, Blome C, Synnergren O, Sheppard J, Caleman C, MacPhee AG, Weinstein D, Lowney DP, Allison T, Matthews T, Falcone RW, Cavalieri AL, Fritz DM, Lee SH, Bucksbaum PH, Reis DA, Rudati J, Macrander AT, Fuoss PH, Kao CC, Siddons DP, Pahl R, Moffat K, Als-Nielsen J, Duesterer S, Ischebeck R, Schlarb H, Schulte-Schrepping H, Schneider J, von der Linde D, Hignette O, Sette F, Chapman HN, Lee RW, Hansen TN, Wark JS, Bergh M, Huldt G, van der Spoel D, Timneanu N, Hajdu J, Akre RA, Bong E, Krejcik P, Arthur J, Brennan S, Luening K, Hastings JB. Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb. PHYSICAL REVIEW LETTERS 2005; 95:125701. [PMID: 16197085 DOI: 10.1103/physrevlett.95.125701] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2005] [Indexed: 05/04/2023]
Abstract
The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs. This structural anisotropy indicates that the initially generated fluid differs significantly from the equilibrium liquid.
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Lindenberg AM, Larsson J, Sokolowski-Tinten K, Gaffney KJ, Blome C, Synnergren O, Sheppard J, Caleman C, Macphee AG, Weinstein D, Lowney DP, Allison TK, Matthews T, Falcone RW, Cavalieri AL, Fritz DM, Lee SH, Bucksbaum PH, Reis DA, Rudati J, Fuoss PH, Kao CC, Siddons DP, Pahl R, Als-Nielsen J, Duesterer S, Ischebeck R, Schlarb H, Schulte-Schrepping H, Tschentscher T, Schneider J, von der Linde D, Hignette O, Sette F, Chapman HN, Lee RW, Hansen TN, Techert S, Wark JS, Bergh M, Huldt G, van der Spoel D, Timneanu N, Hajdu J, Akre RA, Bong E, Krejcik P, Arthur J, Brennan S, Luening K, Hastings JB. Atomic-Scale Visualization of Inertial Dynamics. Science 2005; 308:392-5. [PMID: 15831753 DOI: 10.1126/science.1107996] [Citation(s) in RCA: 292] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids.
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60
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Cavalieri AL, Fritz DM, Lee SH, Bucksbaum PH, Reis DA, Rudati J, Mills DM, Fuoss PH, Stephenson GB, Kao CC, Siddons DP, Lowney DP, Macphee AG, Weinstein D, Falcone RW, Pahl R, Als-Nielsen J, Blome C, Düsterer S, Ischebeck R, Schlarb H, Schulte-Schrepping H, Tschentscher T, Schneider J, Hignette O, Sette F, Sokolowski-Tinten K, Chapman HN, Lee RW, Hansen TN, Synnergren O, Larsson J, Techert S, Sheppard J, Wark JS, Bergh M, Caleman C, Huldt G, van der Spoel D, Timneanu N, Hajdu J, Akre RA, Bong E, Emma P, Krejcik P, Arthur J, Brennan S, Gaffney KJ, Lindenberg AM, Luening K, Hastings JB. Clocking femtosecond X rays. PHYSICAL REVIEW LETTERS 2005; 94:114801. [PMID: 15903864 DOI: 10.1103/physrevlett.94.114801] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Indexed: 05/02/2023]
Abstract
Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of the x-ray pulse duration are hampered by the inability to precisely synchronize an external laser to the accelerator. At the Sub-Picosecond Pulse Source at the Stanford Linear-Accelerator Center we solved this problem by measuring the arrival time of each high energy electron bunch with electro-optic sampling. This measurement indirectly determined the arrival time of each x-ray pulse relative to an external pump laser pulse with a time resolution of better than 60 fs rms.
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DeCamp MF, Reis DA, Fritz DM, Bucksbaum PH, Dufresne EM, Clarke R. X-ray synchrotron studies of ultrafast crystalline dynamics. JOURNAL OF SYNCHROTRON RADIATION 2005; 12:177-192. [PMID: 15728970 DOI: 10.1107/s0909049504033679] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2004] [Accepted: 12/17/2004] [Indexed: 05/24/2023]
Abstract
Ultrafast X-ray experiments at synchrotron sources hold tremendous promise for measuring the atomistic dynamics of materials under a wide variety of transient conditions. In particular, the marriage of synchrotron radiation and ultrafast laser technology is opening up a new frontier of materials research. Structural changes initiated by femtosecond laser pulses can be tracked in real time using time-resolved X-ray diffraction on picosecond time scales or shorter. Here, research at the Advanced Photon Source is described, illustrating the opportunities for ultrafast diffraction with some recent work on the generation of impulsive strain, coherent phonon generation and supersonic diffusion of electron-hole plasmas. The flexibility of time-resolved Bragg and Laue diffraction geometries are both utilized to illuminate the strain generation and evolution process. Time-resolved X-ray science will become increasingly important with the construction of linac-based ultrafast X-ray sources.
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63
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Malinovskaya SA, Bucksbaum PH, Berman PR. On the role of coupling in mode selective excitation using ultrafast pulse shaping in stimulated Raman spectroscopy. J Chem Phys 2004; 121:3434-7. [PMID: 15303906 DOI: 10.1063/1.1774985] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The coherence of two coupled two-level systems, representing vibrational modes in a semiclassical model, is calculated in weak and strong fields for various coupling schemes and for different relative phases between initial state amplitudes. A relative phase equal to pi projects the system into a dark state. The selective excitation of one of the two, two-level systems is studied as a function of coupling strength and initial phases.
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64
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Pearson BJ, Bucksbaum PH. Control of Raman lasing in the nonimpulsive regime. PHYSICAL REVIEW LETTERS 2004; 92:243003. [PMID: 15245081 DOI: 10.1103/physrevlett.92.243003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2003] [Indexed: 05/24/2023]
Abstract
We explore coherent control of stimulated Raman scattering in the nonimpulsive regime. Optical pulse shaping of the coherent pump field leads to control over the stimulated Raman output. A model of the control mechanism is investigated.
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65
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Rangan C, Bloch AM, Monroe C, Bucksbaum PH. Control of trapped-ion quantum states with optical pulses. PHYSICAL REVIEW LETTERS 2004; 92:113004. [PMID: 15089132 DOI: 10.1103/physrevlett.92.113004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2003] [Indexed: 05/24/2023]
Abstract
We present new results on the quantum control of systems with infinitely large Hilbert spaces. A control-theoretic analysis of the control of trapped-ion quantum states via optical pulses is performed. We demonstrate how resonant bichromatic fields can be applied in two contrasting ways--one that makes the system completely uncontrollable and the other that makes the system controllable. In some interesting cases, the Hilbert space of the qubit-harmonic oscillator can be made finite, and the Schrödinger equation controllable via bichromatic resonant pulses. Extending this analysis to the quantum states of two ions, a new scheme for producing entangled qubits is discovered.
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66
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DeCamp MF, Reis DA, Cavalieri A, Bucksbaum PH, Clarke R, Merlin R, Dufresne EM, Arms DA, Lindenberg AM, MacPhee AG, Chang Z, Lings B, Wark JS, Fahy S. Transient strain driven by a dense electron-hole plasma. PHYSICAL REVIEW LETTERS 2003; 91:165502. [PMID: 14611411 DOI: 10.1103/physrevlett.91.165502] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2002] [Indexed: 05/06/2023]
Abstract
We measure transient strain in ultrafast laser-excited Ge by time-resolved x-ray anomalous transmission. The development of the coherent strain pulse is dominated by rapid ambipolar diffusion. This pulse extends considerably longer than the laser penetration depth because the plasma initially propagates faster than the acoustic modes. X-ray diffraction simulations are in agreement with the observed dynamics.
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69
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DeCamp MF, Reis DA, Bucksbaum PH, Adams B, Caraher JM, Clarke R, Conover CW, Dufresne EM, Merlin R, Stoica V, Wahlstrand JK. Coherent control of pulsed X-ray beams. Nature 2001; 413:825-8. [PMID: 11677601 DOI: 10.1038/35101560] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Synchrotrons produce continuous trains of closely spaced X-ray pulses. Application of such sources to the study of atomic-scale motion requires efficient modulation of these beams on timescales ranging from nanoseconds to femtoseconds. However, ultrafast X-ray modulators are not generally available. Here we report efficient subnanosecond coherent switching of synchrotron beams by using acoustic pulses in a crystal to modulate the anomalous low-loss transmission of X-ray pulses. The acoustic excitation transfers energy between two X-ray beams in a time shorter than the synchrotron pulse width of about 100 ps. Gigahertz modulation of the diffracted X-rays is also observed. We report different geometric arrangements, such as a switch based on the collision of two counter-propagating acoustic pulses: this doubles the X-ray modulation frequency, and also provides a means of observing a localized transient strain inside an opaque material. We expect that these techniques could be scaled to produce subpicosecond pulses, through laser-generated coherent optical phonon modulation of X-ray diffraction in crystals. Such ultrafast capabilities have been demonstrated thus far only in laser-generated X-ray sources, or through the use of X-ray streak cameras.
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71
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Reis DA, DeCamp MF, Bucksbaum PH, Clarke R, Dufresne E, Hertlein M, Merlin R, Falcone R, Kapteyn H, Murnane MM, Larsson J, Missalla T, Wark JS. Probing impulsive strain propagation with X-ray pulses. PHYSICAL REVIEW LETTERS 2001; 86:3072-5. [PMID: 11290110 DOI: 10.1103/physrevlett.86.3072] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2000] [Indexed: 05/22/2023]
Abstract
Pump-probe time-resolved x-ray diffraction of allowed and nearly forbidden reflections in InSb is used to follow the propagation of a coherent acoustic pulse generated by ultrafast laser excitation. The surface and bulk components of the strain could be simultaneously measured due to the large x-ray penetration depth. Comparison of the experimental data with dynamical diffraction simulations suggests that the conventional model for impulsively generated strain underestimates the partitioning of energy into coherent modes.
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72
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Ahn J, Hutchinson DN, Rangan C, Bucksbaum PH. Quantum phase retrieval of a Rydberg wave packet using a half-cycle pulse. PHYSICAL REVIEW LETTERS 2001; 86:1179-1182. [PMID: 11178038 DOI: 10.1103/physrevlett.86.1179] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2000] [Indexed: 05/23/2023]
Abstract
A terahertz half-cycle pulse was used to retrieve information stored as quantum phase in an N-state Rydberg atom data register. The register was prepared as a wave packet with one state phase reversed from the others (the "marked bit"). A half-cycle pulse then drove a significant portion of the electron probability into the flipped state via multimode interference.
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73
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Abstract
Information was stored as quantum phase in an N-state Rydberg atom data register. One or more flipped states stored in an eight-state atomic wave packet could be retrieved in a single operation, in agreement with a recent proposal by Grover.
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74
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Lindenberg AM, Kang I, Johnson SL, Missalla T, Heimann PA, Chang Z, Larsson J, Bucksbaum PH, Kapteyn HC, Padmore HA, Lee RW, Wark JS, Falcone RW. Time-resolved X-Ray diffraction from coherent phonons during a laser-induced phase transition. PHYSICAL REVIEW LETTERS 2000; 84:111-4. [PMID: 11015847 DOI: 10.1103/physrevlett.84.111] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/1999] [Indexed: 05/22/2023]
Abstract
Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.
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Larsson J, Chang Z, Judd E, Schuck PJ, Falcone RW, Heimann PA, Padmore HA, Kapteyn HC, Bucksbaum PH, Murnane MM, Lee RW, Machacek A, Wark JS, Liu X, Shan B. Ultrafast x-ray diffraction using a streak-camera detector in averaging mode. OPTICS LETTERS 1997; 22:1012-1014. [PMID: 18185736 DOI: 10.1364/ol.22.001012] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We demonstrate an apparatus for measuring time-dependent x-ray diffraction. X-ray pulses from a synchrotron are diffracted by a pair of Si(111) crystals and detected with an x-ray streak camera that has single-shot resolution of better than 1 ps. The streak camera is driven by a photoconductive switch, which is triggered by 100-fs laser pulses at a repetition rate of 1 kHz. The laser and the streak camera are synchronized with the synchrotron pulses. In the averaging mode, trigger jitter results in 2-ps temporal resolution. We measured the duration of 5-keV pulses from the Advanced Light Source synchrotron to be 70ps.
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