T. Harada

Frustration of direct photoionization of Ar clusters in intense extreme ultraviolet pulses from a free electron laser

We have measured the kinetic energies of fragment ions from Ar clusters (average cluster size N~ 10?600) exposed to intense extreme ultraviolet free electron laser pulses (? ~ 61 nm, I~ 1.3? 1011 W cm?2). For small clusters (N 200), the average kinetic energy of ions strongly increases with increasing the cluster size, indicating a promotion of the multiple ionization, whereas the average kinetic energy is observed to be saturated for N 200. Considering how many photoelectrons can escape from the cluster, it was found that the size dependence of the ion kinetic energy exhibited the frustration of direct photoionization, which resulted from the strong Coulomb potential of the highly ionized cluster.

High throughput and wide field of view EUV microscope for blur-free one-shot imaging of living organisms

We present and demonstrate the use of an extreme ultraviolet (EUV) microscope that was developed in-house. Images are acquired using Bragg reflection multilayer optics and a laser-produced plasma light source. The upper-limit spatial resolution of the EUV microscope is 130 nm with a 10 ns exposure time and 250 x 250 microm(2) field of view. Resolution is superior to that of visible microscopes with the same size of field of view, and the exposure time is short enough to observe fine structures in-vivo. Observation of the cerebral cortex of a mouse is demonstrated.

Phase change observation in reflection multilayers by total electron yield and reflection spectra

Precise optical elements for use in the extreme ultraviolet region are necessary for controlling both the uppermost layer thickness and the reflection phase in a reflection multilayer system. In this study, a phase value corresponding to both the uppermost layer thickness and the reflection phase was derived from the reflectance and total electron yield (TEY) intensity. Mo∕Si multilayers were fabricated on a silicon wafer with various thicknesses of the uppermost Mo layer. Phase values obtained from the reflection and TEY measurements were found to change in accordance with increases in the thickness of the uppermost Mo layer and a concomitant change in the reflection phase.

Frustration of direct photoionizations of rare gas clusters in intense extreme ultraviolet free-electron laser pulses

We performed a momentum imaging measurements of Ar clusters irradiated by extreme ultraviolet free electron laser pulses (61nm 1.3?1011W/cm2) for various cluster sizes. Dominant fragment ions were Ar+ and Ar2+ ions with significant kinetic energy (up to 40eV). This indicates that Ar clusters absorbed many photons, become highly ionized and finally dissociated into many fragments through Coulomb explosion. The size dependence of the ion kinetic energy distribution indicates that larger clusters significantly suffer from the frustration of direct photoelectron emissions and multiple ionizations.

Momentum spectroscopy of fragment ions emitted from Xe clusters irradiated by EUV-FEL at SPring-8

We have studied multiple ionization of Xe clusters by 61-nm 1011−1012 W/cm2extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan. Kinetic energy distributions of Xe+, Xe+2, Xe+3, and Xe+4 ions emitted from Xe clusters were measured.

Frustration of direct photoionizations of Argon clusters irradiated with intense EUV-FEL pulses

We have measured the kinetic energies of fragment ions from Ar clusters (average cluster size ~ 10 to 600) exposed to intense extreme ultraviolet free-electron laser pulses (? ~ 61nm, I ~ 1.3?1011 [W/cm2]). We found that the average kinetic energy of fragment ions was saturated for 200.

Optical constant measurements of the uppermost layer of a reflection multilayer using reflection and total electron yield spectra

Total electron yield (TEY) is a method for obtaining optical constants by measuring the angle dependence of the yield intensity in the soft X-ray region [S. V. Pepper, J. Opt. Soc. Am. 60, 805 (1970)]. In this study, previous methods are extended by rewriting the previous formulae of yield intensity: the intensity was directly related to a reflectance and phase value corresponding to both the thickness of the uppermost layer and the reflection phase. Phase values obtained practically from the reflection and TEY measurements were found to change in accordance with increases in the thickness of the uppermost Mo layer. Refractive indices were derived from the phase differences between the two different phase values corresponding to the variation in the uppermost Mo layer. Practical study showed that the refractive indices of the uppermost Mo layer are close to those of MoO2.