Short-Wavelength Coherent Radiation: Generation and Application最新文献

{"title":"Calculations of High Intensity Multiphoton Ionization and Photoemission from Atoms*","authors":"K. Kulander, K. Schafer, J. Krause","doi":"10.1364/swcr.1991.mc1","DOIUrl":"https://doi.org/10.1364/swcr.1991.mc1","url":null,"abstract":"A surprising array of effects have been observed during high-intensity, short-pulse laser excitation of atoms and molecules. To model these measurements, methods have been developed to solve the time-dependent Schrödinger equation for an atom in a time varying, classical electromagnetic field. Studies on many atomic and molecular systems have been performed over a range of intensities from the regime within which perturbative techniques are valid up to field strengths well above an atomic unit (I > 3.51x1016 W/cm2). These calculations have provided predictions for ionization rates, photoelectron energy and angular distributions and photoemission rates. The effects of ac Stark shifted and intensity broadened intermediate states on the emission processes have been investigated. At high frequency and the highest intensities atoms are found to undergo a transition to a state or states which are surprisingly stable with respect to ionization. This had been predicted using a Floquet approach which did not allow for the time variation of the pulse envelope. The time-dependent calculations, however, show that an appreciable fraction of the electronic wave function can survive the rapid rise of an intense pulse and become stabilized with a greatly reduced ionization rate. Here we present a discussion of some of the most recent results.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126663986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Soft x-ray spectra from laser plasma effectively heated by a pulse train laser","authors":"H. Hirose, T. Hara, K. Andō, Fumiko Negishi-Tsuboi, H. Yashiro","doi":"10.1364/swcr.1991.wa1","DOIUrl":"https://doi.org/10.1364/swcr.1991.wa1","url":null,"abstract":"Considerable progress has been made in the development of soft x-ray laser since 19851-2). Until now a powerful laser of single or double pulses has often been used to produce high density plasma. Recently we observed ASE (amplified spontaneous emission) in some lines of Al X and Al XI in a recombining plasma produced by a very low power laser of only 2 J which was composed of a train of many low power pulses separated by about 350 picosecond3). To understand more clearly the effect of multipulse irradiation on the production of laser plasma and x-ray emissions including ASE, in this paper we constructed a pulse train forming system and investigated the emitted soft x-ray spectra for various pulse trains. Our final goal is to develop a table top x-ray laser in the water window wavelength.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"82 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122668931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral Blueshifts of Femtosecond Pulses in Atmospheric Density Kr and Xe Plasmas","authors":"W. M. Wood, M. Downer","doi":"10.1364/swcr.1991.md3","DOIUrl":"https://doi.org/10.1364/swcr.1991.md3","url":null,"abstract":"Collisionless multiphoton ionization of atmospheric density gases with intense femtosecond pulses can produce a cold, dense plasma of highly stripped ions, thus providing a promising medium for XUV recombination lasers[1]. We have shown in several recent papers [2-4] that rapid ionization and the subsequent development of of plasma temperature in atmospheric density plasmas cause macroscopic refractive index changes which in turn induce characteristic spectral shifts on the ionizing pulse, or a time delayed probing pulse. Theoretical analysis of detailed features of these shifts in the lighter rare gases (He, Ne, Ax) has revealed several key aspects of femtosecond ionization: 1) an ab initio model of spectral shifts based on fundamental strong field ionization theory (e.g. Keldysh, Ammosov [5,6]); 2) the occurence of anomalously large blue shifts at higher pressures and intensities, when the ionization rate is significantly enhanced by impact-ionizing collisions of the quivering electrons [4]; and 3) evidence for low plasma temperatures, based on red shifts induced on a time-delayed probe [4], In this paper we present new results with Kr and Xe gases, which reveal a distinct \"doublehumped\" feature in the blue shifted single pulse spectra not seen in the lighter noble gases. A quantitative model is presented that attributes this effect to two characteristic rates at which multiple stepwise ionization occurs: a \"fast\" rate corresponding to each ionization stage during the early part of the pulse (e.g. Krn+ -> Krn+1)+) that produces the more shifted peak; and a \"slow\" rate which corresponds to the primarily impact ionization during the peak and latter parts of the pulse. The dwell time following the saturation of each ionization level in the early part of the pulse also contributes to a significant broadening of the bluer shifted part of the spectrum. This two-humped effect is more pronounced in Kr and Xe because of the lower ionization potentials, and therefore greater ionization rates; in addition, the larger number of levels ionized in these heavier noble gases cause a greater broadening of the further-shifted peak. Details of the double-humped blue shifted spectra depend on the role of impact ionizing collisions in the strong field, and also on the presence of chirp on the incident pulse.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126069888","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ionization and Dissociation of Molecular Hydrogen by Ultrashort Light Pulses.","authors":"A. Zaviyev, D. Schumacher, F. Weihe, P. Bucksbaum, J. Squier","doi":"10.1364/swcr.1991.mb4","DOIUrl":"https://doi.org/10.1364/swcr.1991.mb4","url":null,"abstract":"Much research has been done lately to investigate the interaction of intense coherent light with molecules. Even simple homonuclear diatomic molecules exhibit very complicated behavior in an intense light field, including multiphoton ionization and dissociation, multiple ionization, above-threshold ionization (ATI), and bondsoftening, which has also been called above-threshold dissociation (ATD).1","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122508394","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transport in ultra-dense plasmas produced by 1 ps laser pulse","authors":"M. Chaker, Y. Beaudoin, J. Kieffer, H. Pépin, C. Chien","doi":"10.1364/swcr.1991.tua2","DOIUrl":"https://doi.org/10.1364/swcr.1991.tua2","url":null,"abstract":"The recent developement of picosecond laser technology1 has made possible the production of extremely-bright laser sources which are used to produce ultra-dense plasmas2. In the present work we describe the first experimental study of transport in ultrashort scalelength plasmas (L/λ « 0,1).","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114251751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Density Profile Steepening by the Ponderomotive Force of an Intense Picosecond Laser","authors":"D. Umstadter, X. Liu, J. Coe, C. Chien","doi":"10.1364/swcr.1991.tua4","DOIUrl":"https://doi.org/10.1364/swcr.1991.tua4","url":null,"abstract":"The high-density plasmas produced by the interaction of short-pulse lasers with solid targets have been proposed as candidate coherent x-ray sources [1]. Large absorption of laser light and rapid cooling of the plasma—both of which are required for this scheme to work—depend strongly on the evolution of the electron-density profile during the laser pulse. We report experimental and theoretical results indicating that when the quiver energy of the electrons exceeds their thermal energy, the ponderomotive pressure of the laser significantly modifies the density profile.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117021286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Search for Gain on 2p-2s Transitions in a Collisionally Excited Ge Plasma","authors":"G. Enright, H. Baldis, J. Dunn, B. Lafontaine, D. Villeneuve","doi":"10.1364/swcr.1991.wa4","DOIUrl":"https://doi.org/10.1364/swcr.1991.wa4","url":null,"abstract":"Soft x-ray amplification in collisionally excited Ne-like Ge plasmas has been extensively studied. Gains in excess of 4 cm-1 have been reported for the 3p-3s transitions. Significant gains have been observed over a wide range of irradiance conditions. The present experiments make use of a novel focusing arrangement[1] that employs a segmented wedge array (SWA) to overlap several line foci to produce a highly uniform linear plasma. The reproducibility of the XUV spectra was improved allowing gain to be inferred on a core-excited 2s2p63d-2s2p63p J=2-1 transition[2]. The 3d-2s quadrupole (E2) emission from the upper state of this transition was also identified in the L-shell emission spectrum. These measurements have now been extended into the 60-80 Å region where gain on 2s2p63s-2s2p53s and 2s2p63d-2s22p63d transitions is expected. Observation of gain on these Ne-like transitions would be significant as it would allow Ne-like lasers to scale to shorter wavelengths, into the \"water window\".","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131208399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Integration of the Schrödinger Equation on a Massively Parallel Processor","authors":"J. Parker, S. Blodgett-Ford, C. Clark","doi":"10.1364/swcr.1991.tua6","DOIUrl":"https://doi.org/10.1364/swcr.1991.tua6","url":null,"abstract":"The behavior of atoms in strong radiation fields depends critically upon the time evolution of the field. For example, it has been found1 that above-threshold ionization (ATI) spectra show radical changes as the duration of the exciting laser pulse decreases; there is also theoretical evidence2 for novel phenomena, such as population trapping, which occur only for relatively short pulses. In order to treat problems of this sort theoretically, one must employ methods that accommodate general time variation of the radiation field. The most direct such method is numerical integration of the time-dependent Schrödinger equation. This would be an entirely non-controversial approach if vast computational resources were not required to implement it in practice. To date there have been only a few reports3 of direct integration of the time-dependent Schrodinger equation for a three dimensional, one-electron atom in a radiation field.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114264377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Harmonic Generation by an Intense Picosecond Laser in an Underdense Plasma","authors":"X. Liu, J. Coe, C. Chien, D. Umstadter","doi":"10.1364/swcr.1991.mc4","DOIUrl":"https://doi.org/10.1364/swcr.1991.mc4","url":null,"abstract":"Modest power lasers interacting with a neutral gas have been observed to produce coherent harmonic radiation (up to the 61\u0000 st\u0000 harmonic) at odd multiples of the fundamental laser frequency[1]. This is a result of the laser field causing the bound electrons to oscillate in the anharmonic atomic potential. The process is limited to relatively low powers since increasing the fundamental laser power leads to ionization of the gas and to the production of unbound electrons. A very high-power laser interacting with a fully ionized plasma, however, may lead to the generation of large levels of coherent radiation at high harmonics (including even harmonics) of the incident laser frequency based on an entirely new mechanism. If the laser pulse is sufficiently intense, the plasma electron mass becomes modulated because of nonlinear relativistic effects [2]. We describe in this paper the theory and some experiments in which we observe signatures of this mechanism.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"315 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116811413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Creation of relativistic plasmas using ultra-high-intensity laser radiation","authors":"J. Bardsley, B. Penetrante","doi":"10.1364/swcr.1991.tub1","DOIUrl":"https://doi.org/10.1364/swcr.1991.tub1","url":null,"abstract":"Theories of ponderomotive forces, relativistic focusing, and harmonic generation are reviewed, and nonlinear effects are demonstrated by using numerical simulations of plasmas produced by subpicosecond lasers.","PeriodicalId":286766,"journal":{"name":"Short-Wavelength Coherent Radiation: Generation and Application","volume":"1972 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130317672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}