We report an observation of essentially full spatial coherence in a high average power soft-x-ray laser. Rapid coherence buildup due to strong refractive antiguiding in a long plasma column is experimentally demonstrated. This allows the generation of fully coherent, milliwatt-level average power soft-x-ray radiation by a tabletop device. The peak brightness of this laser reaches 2ϫ10 25 photons s Ϫ1 mm Ϫ2 mrad Ϫ2 within 0.01% spectral bandwidth, making it one of the brightest soft-x-ray sources available. Applications such as high-resolution microscopy, interferometry, lithography, and holography motivate the development of advanced light sources at soft-x-ray wavelengths. Current approaches for the generation of high brightness coherent radiation in this spectral region include undulators at modern synchrotron radiation ͑SR͒ facilities ͓1͔, high-order harmonic generation ͑HHG͒ of optical lasers ͓3,4͔, and softx-ray lasers ͓2͔. The degree of spatial coherence of radiation plays a critical role in many of the most important applications. For SR sources, high spatial coherence is achieved at the expense of photon flux by spatial filtering ͓1͔. HHG sources driven by coherent optical lasers have shown high spatial coherence with average powers reaching the order of microwatts by using a phase-matching technique ͓4͔. Compared with SR and HHG sources, soft-x-ray lasers have substantially higher pulse energy and narrower linewidth. However, to date they have been characterized by rather low spatial coherence ͓5-9͔. The demonstration of nearly full spatial coherence has been one of the main goals of soft-xray laser research.Soft-x-ray laser beams are generally limited to single-pass or double-pass amplification of spontaneous emission ͑ASE͒ through the plasma. From the van Cittert-Zernike theorem ͓10͔, a high degree of spatial coherence from an ASE-based laser can be achieved when the gain medium has a Fresnel number less than unity. However, this is difficult to achieve in a plasma column, unless some forms of spatial filtering are used ͓11,12͔. Here we experimentally demonstrate that refraction in a plasma with sharp density gradients can reduce the effective transverse source size significantly and result in essentially full spatial coherence. Although theoretical results have suggested that refractive antiguiding and gain guiding along a long plasma column could result in improved spatial coherence ͓13-15͔, in previous experiments the coherence buildup was limited to values significantly below full coherence ͓7,16͔. In the present work, we utilized fast capillary discharge excitation to produce plasma columns with both very high axial uniformity and the length-todiameter ratio exceeding 1000:1, in which strong refractive antiguiding makes it possible to achieve essentially full spatial coherence with a plasma column length of 36 cm.The laser beam in our experiments is generated by excitation of an Ar-filled capillary channel with a fast discharge current pulse that rapidly compresses the plasma to form a dense and ...

We report the demonstration of laser amplification at 52.9 nm in Ne-like Cl with a compact capillary discharge. Laser output pulses with energies of as much as 10 muJ have been obtained. The beam divergence was approximately 4 mrad. This new 23.4-eV tabletop laser is of particular interest for applications that require high peak fluxes of photons with energy slightly below the He photoionization threshold.

Abstract.For many years, researchers have envisioned the development of compact high repetition rate tabletop soft X-ray lasers that could be routinely used in application in numerous disciplines. With demonstrated average powers of several mW and mJ-level pulse energy at 46.9 nm, capillary discharge-pumped lasers are the first compact lasers to reach this goal. In this paper we summarize the development status of high repetition rate tabletop soft X-ray lasers based on capillary discharge excitation, and give examples of their successful use in several applications. Results of the use of a capillary discharge pumped 46.9 nm laser in dense plasma interferometry, soft X-ray reflectometry for the determination of optical constants, and laser ablation are described. The observation of lasing at 53 nm line in Ne-like Cl with output pulse energy up to 10 µJ is also reported. © 2000 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS tabletop soft X-ray lasers Vers de nouvelles longueurs d'onde et applications pour les lasers X-UV compacts à décharge capillaire Résumé. Depuis de nombreuse années, les chercheurs prévoient le développement de laser X-UV compacts, dits « de table », qui pourraient être utilisés en routine pour les applications à des disciplines variées. Avec des puissances moyennes mesurées de plusieurs

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We have demonstrated the use of a high-repetition-rate 46.9-nm tabletop laser to characterize diffraction gratings designed for grazing-incidence operation in the soft-x-ray spectral region. The efficiencies for various diffraction orders were measured as a function of angle of incidence and compared with the results of model simulations. This measurement technique provides benchmarks with which to improve electromagnetic codes used in the design of soft-x-ray diffraction gratings. The results illustrate the potential of compact tabletop soft-x-ray lasers for use as a new tool for characterization of shortwavelength optics at the manufacturer's site.