共查询到20条相似文献，搜索用时 359 毫秒
1.
Modern laser technology has revolutionized the sensitivity and precision of spectroscopy by providing coherent light in a spectrum spanning the infrared, visible, and ultraviolet wavelength regimes. However, the generation of shorter-wavelength coherent pulses in the x-ray region has proven much more challenging. The recent emergence of high harmonic generation techniques opens the door to this possibility. Here we review the new science that is enabled by an ability to manipulate and control electrons on attosecond time scales, ranging from new tabletop sources of coherent x-rays to an ability to follow complex electron dynamics in molecules and materials. We also explore the implications of these advances for the future of molecular structural characterization schemes that currently rely so heavily on scattering from incoherent x-ray sources. 相似文献
2.
Colombelli R Srinivasan K Troccoli M Painter O Gmachl CF Tennant DM Sergent AM Sivco DL Cho AY Capasso F 《Science (New York, N.Y.)》2003,302(5649):1374-1377
We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics. 相似文献
3.
Park HG Kim SH Kwon SH Ju YG Yang JK Baek JH Kim SB Lee YH 《Science (New York, N.Y.)》2004,305(5689):1444-1447
We report the experimental demonstration of an electrically driven, single-mode, low threshold current (approximately 260 microA) photonic band gap laser operating at room temperature. The electrical current pulse is injected through a sub-micrometer-sized semiconductor wire at the center of the mode with minimal degradation of the quality factor. The actual mode of interest operates in a nondegenerate monopole mode, as evidenced through the comparison of the measurement with the computation based on the actual fabricated structural parameters. As a small step toward a thresholdless laser or a single photon source, this wavelength-size photonic crystal laser may be of interest to photonic crystals, cavity quantum electrodynamics, and quantum information communities. 相似文献
4.
We demonstrate polarization mode selection in a two-dimensional (2D) photonic crystal laser by controlling the geometry of the unit cell structure. As the band diagram of the square-lattice photonic crystal is influenced by the unit cell structure, calculations reveal that changing the structure from a circular to an elliptical geometry should result in a strong modification of the electromagnetic field distributions at the band edges. Such a structural modification is expected to provide a mechanism for controlling the polarization modes of the emitted light. A square-lattice photonic crystal with the elliptical unit cell structure has been fabricated and integrated with a gain media. The observed coherent 2D lasing action with a single wavelength and controlled polarization is in good agreement with the predicted behavior. 相似文献
5.
Popmintchev T Chen MC Popmintchev D Arpin P Brown S Alisauskas S Andriukaitis G Balciunas T Mücke OD Pugzlys A Baltuska A Shim B Schrauth SE Gaeta A Hernández-García C Plaja L Becker A Jaron-Becker A Murnane MM Kapteyn HC 《Science (New York, N.Y.)》2012,336(6086):1287-1291
High-harmonic generation (HHG) traditionally combines ~100 near-infrared laser photons to generate bright, phase-matched, extreme ultraviolet beams when the emission from many atoms adds constructively. Here, we show that by guiding a mid-infrared femtosecond laser in a high-pressure gas, ultrahigh harmonics can be generated, up to orders greater than 5000, that emerge as a bright supercontinuum that spans the entire electromagnetic spectrum from the ultraviolet to more than 1.6 kilo-electron volts, allowing, in principle, the generation of pulses as short as 2.5 attoseconds. The multiatmosphere gas pressures required for bright, phase-matched emission also support laser beam self-confinement, further enhancing the x-ray yield. Finally, the x-ray beam exhibits high spatial coherence, even though at high gas density the recolliding electrons responsible for HHG encounter other atoms during the emission process. 相似文献
6.
Witte S Zinkstok RT Ubachs W Hogervorst W Eikema KS 《Science (New York, N.Y.)》2005,307(5708):400-403
Precision spectroscopy at ultraviolet and shorter wavelengths has been hindered by the poor access of narrow-band lasers to that spectral region. We demonstrate high-accuracy quantum interference metrology on atomic transitions with the use of an amplified train of phase-controlled pulses from a femtosecond frequency comb laser. The peak power of these pulses allows for efficient harmonic upconversion, paving the way for extension of frequency comb metrology in atoms and ions to the extreme ultraviolet and soft x-ray spectral regions. A proof-of-principle experiment was performed on a deep-ultraviolet (2 x 212.55 nanometers) two-photon transition in krypton; relative to measurement with single nanosecond laser pulses, the accuracy of the absolute transition frequency and isotope shifts was improved by more than an order of magnitude. 相似文献
7.
Ultrafast spectroscopy was used to study vibrational energy transfer between vibrational reporter groups on different parts of a molecule in a liquid. When OH stretching vibrations of different alcohols were excited by mid-infrared laser pulses, vibrational energy was observed to move through intervening CH2 or CH groups, taking steps up and down in energy, ending up at terminal CH3 groups. For each additional CH2 group in the path between OH and CH3, the time for vibrational energy transfer increased by about 0.4 picosecond. 相似文献
8.
Drescher M Hentschel M Kienberger R Tempea G Spielmann C Reider GA Corkum PB Krausz F 《Science (New York, N.Y.)》2001,291(5510):1923-1927
Single soft-x-ray pulses of approximately 90-electron volt (eV) photon energy are produced by high-order harmonic generation with 7-femtosecond (fs), 770-nanometer (1.6 eV) laser pulses and are characterized by photoionizing krypton in the presence of the driver laser pulse. By detecting photoelectrons ejected perpendicularly to the laser polarization, broadening of the photoelectron spectrum due to absorption and emission of laser photons is suppressed, permitting the observation of a laser-induced downshift of the energy spectrum with sub-laser-cycle resolution in a cross correlation measurement. We measure isolated x-ray pulses of 1.8 (+0.7/-1.2) fs in duration, which are shorter than the oscillation cycle of the driving laser light (2.6 fs). Our techniques for generation and measurement offer sub-femtosecond resolution over a wide range of x-ray wavelengths, paving the way to experimental attosecond science. Tracing atomic processes evolving faster than the exciting light field is within reach. 相似文献
9.
Huismans Y Rouzée A Gijsbertsen A Jungmann JH Smolkowska AS Logman PS Lépine F Cauchy C Zamith S Marchenko T Bakker JM Berden G Redlich B van der Meer AF Muller HG Vermin W Schafer KJ Spanner M Ivanov MY Smirnova O Bauer D Popruzhenko SV Vrakking MJ 《Science (New York, N.Y.)》2011,331(6013):61-64
Ionization is the dominant response of atoms and molecules to intense laser fields and is at the basis of several important techniques, such as the generation of attosecond pulses that allow the measurement of electron motion in real time. We present experiments in which metastable xenon atoms were ionized with intense 7-micrometer laser pulses from a free-electron laser. Holographic structures were observed that record underlying electron dynamics on a sublaser-cycle time scale, enabling photoelectron spectroscopy with a time resolution of almost two orders of magnitude higher than the duration of the ionizing pulse. 相似文献
10.
A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers. 相似文献
11.
van der Wal CH Eisaman MD André A Walsworth RL Phillips DF Zibrov AS Lukin MD 《Science (New York, N.Y.)》2003,301(5630):196-200
We experimentally demonstrate emission of two quantum-mechanically correlated light pulses with a time delay that is coherently controlled via temporal storage of photonic states in an ensemble of rubidium atoms. The experiment is based on Raman scattering, which produces correlated pairs of spin-flipped atoms and photons, followed by coherent conversion of the atomic states into a different photon beam after a controllable delay. This resonant nonlinear optical process is a promising technique for potential applications in quantum communication. 相似文献
12.
Collet E Lemée-Cailleau MH Buron-Le Cointe M Cailleau H Wulff M Luty T Koshihara SY Meyer M Toupet L Rabiller P Techert S 《Science (New York, N.Y.)》2003,300(5619):612-615
We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-p-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level. 相似文献
13.
Schoenlein RW Chattopadhyay S Chong HH Glover TE Heimann PA Shank CV Zholents AA Zolotorev MS 《Science (New York, N.Y.)》2000,287(5461):2237-2240
Femtosecond synchrotron pulses were generated directly from an electron storage ring. An ultrashort laser pulse was used to modulate the energy of electrons within a 100-femtosecond slice of the stored 30-picosecond electron bunch. The energy-modulated electrons were spatially separated from the long bunch and used to generate approximately 300-femtosecond synchrotron pulses at a bend-magnet beamline, with a spectral range from infrared to x-ray wavelengths. The same technique can be used to generate approximately 100-femtosecond x-ray pulses of substantially higher flux and brightness with an undulator. Such synchrotron-based femtosecond x-ray sources offer the possibility of applying x-ray techniques on an ultrafast time scale to investigate structural dynamics in condensed matter. 相似文献
14.
Nam SW Chung HS Lo YC Qi L Li J Lu Y Johnson AT Jung Y Nukala P Agarwal R 《Science (New York, N.Y.)》2012,336(6088):1561-1566
Phase-change materials undergo rapid and reversible crystalline-to-amorphous structural transformation and are being used for nonvolatile memory devices. However, the transformation mechanism remains poorly understood. We have studied the effect of electrical pulses on the crystalline-to-amorphous phase change in a single-crystalline Ge(2)Sb(2)Te(5) (GST) nanowire memory device by in situ transmission electron microscopy. We show that electrical pulses produce dislocations in crystalline GST, which become mobile and glide in the direction of hole-carrier motion. The continuous increase in the density of dislocations moving unidirectionally in the material leads to dislocation jamming, which eventually induces the crystalline-to-amorphous phase change with a sharp interface spanning the entire nanowire cross section. The dislocation-templated amorphization explains the large on/off resistance ratio of the device. 相似文献
15.
We used strong-field laser pulses that were tailored with closed-loop optimal control to govern specified chemical dissociation and reactivity channels in a series of organic molecules. Selective cleavage and rearrangement of chemical bonds having dissociation energies up to approximately 100 kilocalories per mole (about 4 electron volts) are reported for polyatomic molecules, including (CH3)2CO (acetone), CH3COCF3 (trifluoroacetone), and C6H5COCH3 (acetophenone). Control over the formation of CH(3)CO from (CH3)2CO, CF3 (or CH3) from CH3COCF3, and C6H5CH3 (toluene) from C6H5COCH3 was observed with high selectivity. Strong-field control appears to have generic applicability for manipulating molecular reactivity because the tailored intense laser fields (about 10(13) watts per square centimeter) can dynamically Stark shift many excited states into resonance, and consequently, the method is not confined by resonant spectral restrictions found in the perturbative (weak-field) regime. 相似文献
16.
Gibson EA Paul A Wagner N Tobey R Gaudiosi D Backus S Christov IP Aquila A Gullikson EM Attwood DT Murnane MM Kapteyn HC 《Science (New York, N.Y.)》2003,302(5642):95-98
We demonstrate enhanced generation of coherent light in the "water window" region of the soft x-ray spectrum at 4.4 nanometers, using quasi-phase-matched frequency conversion of ultrafast laser pulses. By periodically modulating the diameter of a gas-filled hollow waveguide, the phase mismatch normally present between the laser light and the generated soft x-ray light can be partially compensated. This makes it possible to use neon gas as the nonlinear medium to coherently convert light up to the water window, illustrating that techniques of nonlinear optics can be applied effectively in the soft x-ray region of the spectrum. These results advance the prospects for compact coherent soft x-ray sources for applications in biomicroscopy and in chemical spectroscopy. 相似文献
17.
Mairesse Y de Bohan A Frasinski LJ Merdji H Dinu LC Monchicourt P Breger P Kovacev M Taïeb R Carré B Muller HG Agostini P Salières P 《Science (New York, N.Y.)》2003,302(5650):1540-1543
Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attoseconds in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter. 相似文献
18.
Jones DJ Diddams SA Ranka JK Stentz A Windeler RS Hall JL Cundiff ST 《Science (New York, N.Y.)》2000,288(5466):635-640
We stabilized the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. We confirmed control of the pulse-to-pulse carrier-envelope phase using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which we used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock. 相似文献
19.
We report on stimulated Raman scattering in an approximately 1-meter-long hollow-core photonic crystal fiber filled with hydrogen gas under pressure. Light was guided and confined in the 15-micrometer-diameter hollow core by a two-dimensional photonic bandgap. Using a pulsed laser source (pulse duration, 6 nanoseconds; wavelength, 532 nanometers), the threshold for Stokes (longer wavelength) generation was observed at pulse energies as low as 800 +/- 200 nanojoules, followed by a coherent anti-Stokes (shorter wavelength) generation threshold at 3.4 +/- 0.7 microjoules. The pump-to-Stokes conversion efficiency was 30 +/- 3% at a pulse energy of only 4.5 microjoules. These energies are almost two orders of magnitude lower than any other reported energy, moving gas-based nonlinear optics to previously inaccessible parameter regimes of high intensity and long interaction length. 相似文献
20.
The application of the chirped-pulse amplification technique to solid-state lasers combined with the availability of broad-bandwidth materials has made possible the development of small-scale terawatt and now even petawatt (1000-terawatt) laser systems. The laser technology used to produce these intense pulses and examples of new phenomena resulting from the application of these systems to atomic and plasma physics are described. 相似文献