Influencing supercontinuum generation by phase distorting an ultrashort laser pulse.

We show that the spectral distribution of the supercontinuum (SC) generated in barium fluoride is amenable to alteration simply by controlling the second- and third-order phase distortion of incident femtosecond-duration pulses. The second- and third-order phase distortions are controlled by an acoustic-optic programmable dispersive filter (AOPDF). The spectral extent on the blue side of the SC is influenced by independently varying the phase distortion of an ultrashort laser pulse.

Selective breaking of bonds in water with intense, 2-cycle, infrared laser pulses.

One of the holy grails of contemporary science has been to establish the possibility of preferentially breaking one of several bonds in a molecule. For instance, the two O-H bonds in water are equivalent: given sufficient energy, either one of them is equally likely to break. We report bond-selective molecular fragmentation upon application of intense, 2-cycle pulses of 800 nm laser light: we demonstrate up to three-fold enhancement for preferential bond breaking in isotopically substituted water (HOD). Our experimental observations are rationalized by means of ab initio computations of the potential energy surfaces of HOD, HOD(+), and HOD(2+) and explorations of the dissociation limits resulting from either O-H or O-D bond rupture. The observations we report present a formidable theoretical challenge that need to be taken up in order to gain insights into molecular dynamics, strong field physics, chemical physics, non-adiabatic processes, mass spectrometry, and time-dependent quantum chemistry.

Carrier-envelope-phase effects in ultrafast strong-field ionization dynamics of multielectron systems: Xe and CS2.

Carrier-envelope-phase- (CEP) stabilized 5 and 22 fs pulses of intense 800 nm light are used to probe the strong-field ionization dynamics of xenon and carbon disulfide. We compare ion yields obtained with and without CEP stabilization. With 8-cycle (22 fs) pulses, Xe(6+) yields are suppressed (relative to Xe(+)) by 30%-50%, depending on phase, reflecting the phase dependence of nonsequential ionization and its contribution to the formation of higher charge states. Ion yields for Xe(q+) (q = 2-4) with CEP-stabilized pulses are enhanced (by up to 50%) compared to those with CEP-unstabilized pulses. Such enhancement is particularly pronounced with 2-cycle (5 fs) pulses and is distinctly phase dependent. Orbital shape and symmetry affect how CS(2) responds to variations in optical field that are effected as CEP is altered, keeping intensity constant. Molecular fragmentation is found to depend on field strength (not intensity); the relative enhancement of fragmentation when CEP-stabilized 2-cycle pulses are used is found to be at the expense of molecular ionization.

Intense two-cycle laser pulses induce time-dependent bond hardening in a polyatomic molecule.

A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules such as TMS do not exhibit a prominent molecular ion (TMS(+)) as unimolecular dissociation into [Si(CH(3))(3)](+) proceeds very fast. Under a strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond hardening: a field-induced potential well is created in the TMS(+) potential energy curve that effectively traps a wave packet. The time dependence of this bond-hardening process is verified using longer-duration (≥100 fs) pulses; the relatively slower falloff of optical field in such pulses allows the initially trapped wave packet to leak out, thereby rendering TMS(+) unstable once again.

Telecytology in Hokkaido Island, Japan: results of primary telecytodiagnosis of routine cases.

In 1997, an Internet-based static image telepathology system was built at Sapporo National Hospital, Japan. We can exchange high-resolution microscopical images through a file transfer protocol server and discuss cytological findings and diagnosis on an electronic mailing list. We applied the system to primary telecytodiagnosis. From May 1997 to April 1999 we have made diagnoses of 614 daily cases only by looking at the video monitor images transmitted from the cytotechnologist of Wakkanai Municipal Hospital 300 km distant from Sapporo. The concordance between telecytodiagnosis and glass slide diagnosis was 88.6%. Kappa statistics for cervical smears was 0.919 and that for specimens other than uterine cervix was 0.810. The accuracy of telecytodiagnosis was 91.4%, and was not substantially different from that of the conventional mail-based cytology in a previous year. We had five cases with a severely inappropriate diagnosis in telecytology, all of which however were quickly corrected by follow-up histological or cytological specimens. With the use of an electronic mailing list the participants had quick and sufficient discussions. We conclude that telecytology is very useful for primary cytodiagnosis in regional medicine and that it may raise the accuracy of cytodiagnosis in future, if we make consistent efforts to reflect the benefits of telecytology in daily practices. This is the first report of clinical results of telecytology from Japan.