We report the demonstration of an amplitude-division soft-x-ray interferometer that can be used to generate high-contrast interferograms at the wavelength of any of the saturated soft-x-ray lasers (5.6 -46.9 nm) that are available at present. The interferometer, which utilizes grazing-incidence diffraction gratings as beam splitters in a modif ied Mach -Zehnder conf iguration, was used in combination with a tabletop 46.9-nm laser to probe a large-scale ͑ϳ2.7-mm-long͒ laser-created plasma.

Light microscopy has greatly advanced our understanding of nature. The achievable resolution, however, is limited by optical wavelengths to Ϸ200 nm. By using imaging and labeling technologies, resolutions beyond the diffraction limit can be achieved for specialized specimens with techniques such as near-field scanning optical microscopy, stimulated emission depletion microscopy, and photoactivated localization microscopy. Here, we report a versatile soft x-ray diffraction microscope with 70-to 90-nm resolution by using two different tabletop coherent soft x-ray sources-a soft x-ray laser and a high-harmonic source. We also use field curvature correction that allows high numerical aperture imaging and neardiffraction-limited resolution of 1.5. A tabletop soft x-ray diffraction microscope should find broad applications in biology, nanoscience, and materials science because of its simple optical design, high resolution, large depth of field, 3D imaging capability, scalability to shorter wavelengths, and ultrafast temporal resolution.imaging ͉ lensless ͉ nanoscale ͉ extreme-ultraviolet ͉ ultrafast

We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain -length product GL of 15.5 is obtained in the 4d 1 S 0 4p 1 P 1 laser line of Ni-like Mo in plasmas heated at grazing incidence with ϳ1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm. There is great interest in the development of compact saturated high-repetition-rate lasers capable of producing significant average output powers at soft-x-ray wavelengths for applications. Ne-like Ar capillary-discharge-pumped lasers operating at repetition rates of up to 10 Hz have been demonstrated to produce milliwatt average powers at 46.9 nm. 1,2More recently, saturated optical f ield ionization lasers operating in Pd-like Xe at 41.8 nm and in Ni-like Kr at 32.8 nm were obtained by use of 0.33-and 0.76-J pulses, respectively, from a femtosecond 10-Hz pump laser. 3,4 Longitudinal pumping of Mo plasma with short pulses from 10-Hz lasers produced nonsaturated amplification at 18.9 nm in Ni-like Mo, 5,6 a laser line first observed in a small-scale pump system using 80-ps pump pulses. 7Transient collisional electron excitation of targets at normal incidence with 3-10 J of pump energy has produced several saturated lasers in the 12-33-nm range at repetition rates of one shot every several minutes. 8,9 Excitation of a Mo target with 150-fs, 300-mJ pulses impinging at 60 ± from normal incidence resulted in the appearance of the 18.9-and 22.6-nm laser lines of Ni-like Mo. 10 Recently, it was shown that the pumping energy necessary for lasing could be significantly reduced by directing the short pulse onto the target at grazing incidence. 11,12This inherently traveling-wave pumping geometry takes advantage of the refraction of the pump beam to increase the path length of the rays in the gain region of the plasma, thereby increasing the fraction of the pump energy absorbed in that region. A gain -length product of ϳ15 was reported in the 18.9-nm line of Ni-like Mo with 150 mJ of total pumping energy from a 10-Hz laser. 13A normal-incidence 200-ps prepulse was focused into a 15-mm-wide line focus and followed by a 1.5-ps short pulse impinging at a grazing-incidence angle of 14 ± . Lasing was observed to occur over only an extremely narrow ϳ50-ps range of prepulse-to-short-pulse time delays.Herein, we report saturated laser operation in the 18.9-nm line of Ni-like Mo and strong amplif ication at 22.6 nm by use of a 5 -10-Hz tabletop pump laser.Lasing was obtained over a very broad range of time delays. The gain medium was created by the combination of laser pulses generated by an 800-nm tabletop Ti:sapphire laser system with three stages of amplification. A beam splitter directed 20% of the third-stage output to the prepulse arm (120 ps FWHM, 350 mJ), and the re...

We have directly probed the conditions in which the Ni-like Pd transient collisional x-ray laser is generated and propagates by measuring the near-field image and by utilizing picosecond resolution soft x-ray laser interferometry of the preformed Pd plasma gain medium. The electron density and gain region of the plasma have been determined experimentally and are found to be in good agreement with simulations. We observe a strong dependence of the laser pump-gain medium coupling on the laser pump parameters. The most efficient coupling occurs with the formation of lower density gradients in the preformed plasma and when the duration of the main heating pulse is comparable to the gain lifetime ͑ϳ10 ps for mid-Z Ni-like schemes͒. This increases the output intensity by more than an order of magnitude relative to the commonly utilized case where the same pumping energy is delivered within a shorter heating pulse duration ͑Ͻ3 ps͒. In contrast, the higher intensity heating pulses are observed to be absorbed at higher electron densities and in regions where steep density gradients limit the effective length of the gain medium. A detailed understanding of the plasma that constitutes the gain medium is crucial for the development of efficient x-ray lasers. Use of the prepulse technique has allowed x-ray lasers to achieve saturated output using many different elements for the lasing media ͓1͔. However, even the best laser-pumped x-ray lasers typically have an efficiency of 10 −6 . In the transient collisional excitation ͑TCE͒ scheme a low intensity long pulse preforms a plasma, which is allowed to expand and cool before being heated by a high intensity short pulse ͓2͔. This short pulse, in some cases with subpicosecond duration, rapidly heats the plasma to generate a high gain coefficient, saturated x-ray laser output ͓3͔, and x-ray laser pulses as short as 2 ps ͓4͔. In experiments reported on high power laser drivers the pulse duration of the short pulse generated by chirped pulse amplification ͑CPA͒ is in the range of 0.3-3 ps ͓3-7͔. It has been assumed to some extent that by maximizing the intensity of the main heating pulse the temperature, collisional pumping, and local gain coefficient will also be maximized. Under these conditions the lowest saturated wavelength currently demonstrated is 7.3 nm for Nilike Sm ͓5͔.To improve the efficiency we need to better understand the laser-plasma coupling and plasma characteristics of the x-ray laser media. In this paper we combine the techniques of near-field imaging with recently developed picosecond x-ray laser interferometry ͓8͔ to characterize the lasing medium for a Ni-like Pd x-ray laser. It is observed that a combination of controlling and reducing the plasma density gradients while matching the duration of the main pumping pulse to the gain lifetime at a specific density optimizes the coupling efficiency. This increases the x-ray laser output by an order of magnitude over the case where the same pumping energy is delivered into a higher intensity, shorter pulse. In contr...

The authors present a self-imaging lithographic technique, capable of patterning large area periodic structures of arbitrary content with nanoscale resolution. They start from the original concept of Talbot imaging of binary gratings-and introduce the generalized Talbot imaging ͑GTI͒ where periodic structures of arbitrary shape and content form high-definition self-images. This effect can be used to create the complex, periodic patterns needed in the many lithographic fabrication steps of modern semiconductor devices. Since the process is diffraction limited, the achievable resolution depends only on the wavelength, mask patterning, and degree of coherence of the source. Their approach removes all the complex extreme ultraviolet ͑EUV͒ reflective masks and optics, replacing them with nanopatterned transmission masks and makes the whole process simple and cost effective. They have successfully verified the GTI concept using first a He-Ne laser, and then demonstrated its potential as a nanolithography method using a compact table-top soft x-ray ͑EUV͒ 46.9 nm laser source. These sources provide the high degree of coherence needed by diffraction-based imaging and are extendable to shorter wavelengths. They have recorded EUV GTI images up to the sixth Talbot plane, with consistent high quality good results, clearly demonstrating the ability of the GTI method to record high-resolution patterns at large distances.

As an in-plane charge current flows in a heavy metal film with spin–orbit coupling, it produces a torque on and thereby switches the magnetization in a neighbouring ferromagnetic metal film. Such spin–orbit torque (SOT)-induced switching has been studied extensively in recent years and has shown higher efficiency than switching using conventional spin-transfer torque. Here we report the SOT-assisted switching in heavy metal/magnetic insulator systems. The experiments used a Pt/BaFe12O19 bilayer where the BaFe12O19 layer exhibits perpendicular magnetic anisotropy. As a charge current is passed through the Pt film, it produces a SOT that can control the up and down states of the remnant magnetization in the BaFe12O19 film when the film is magnetized by an in-plane magnetic field. It can reduce or increase the switching field of the BaFe12O19 film by as much as about 500 Oe when the film is switched with an out-of-plane field.

Starting with the discovery of x-ray lasers in 1984, laser-created plasmas remained for almost a decade, the only medium in which large amplification of soft-x-ray radiation could be obtained. In this paper the recent first demonstration of large soft-x-ray amplification in a discharge-created plasma column, realized utilizing a fast capillary discharge to collisionally excite the 46.9 nm transition of Ne-like, Ar is reviewed. Results of the parametrization of the Ar IX discharge-pumped amplifier, the study of the dynamics of its plasma column, and the measurement of the time history of the laser pulse are reported. Prospects for laser operation at shorter wavelengths are also discussed. 0 1995 American Institute of Physics.

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 m of the target surface. A series of highquality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.