Soft X-ray characterization of an elongated gas-puff target dedicated for laser–matter interaction experiments and high harmonic generation P.W. Wachulak ⇑ , A. Bartnik, H. Fiedorowicz, R. Jarocki, J. Kostecki, M. Szczurek Institute of Optoelectronics, Military University of Technology, ul. Gen. S. Kaliskiego 2, 00-908 Warsaw, Poland article info Article history: Received 18 October 2011 Received in revised form 19 January 2012 Available online 30 January 2012 Keywords: Soft X-rays Soft X-ray measurements Gas-puff target Laser applications Laser-produced plasma Backlighting method High harmonic generation abstract A slit-shaped elongated nozzle, capable of forming an extended gas density profile, is presented and stud- ied in detail. Argon and xenon target density backlighting measurements revealed the elongated density profiles with gas density that can be tuned by changing valve backing pressure and valve timing. Two dimensional density maps for Ar and Xe targets, obtained at soft X-ray wavelengths around 7 Å, are shown and spatially characterized. Moreover the influence of valve backing pressure and valve timing on gas puff target density is studied. This geometry of the nozzle has potential applications in high har- monic generation for an efficient conversion of femto-second duration, intense infrared pulses to extreme ultraviolet (EUV) region. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Studies of laser-matter interactions promote the accelerated development of compact extreme ultraviolet (EUV) and soft X- ray (SXR) sources. A strong demand for such sources is driven by the opportunity to perform experiments, previously restricted to large synchrotron and free electron laser facilities, on table top in the comfort of own laboratory. Moreover the strong interest for high photon flux sources comes also from semiconductor industry, striving for even smaller, faster and less power consuming com- puter chips [1]. The usability of the EUV sources was demonstrated in many experiments involving compact table top EUV sources such as cap- illary discharge lasers for the interferometric lithography (IL) [2,3] and wavelength resolution holography [4], diffraction imaging [5], EUV microscopy [6], high-harmonic generation (HHG) sources [7,8] for the lens-less imaging [9] and surface deformation studies [10], optically pumped EUV lasers in the EUV microscopy with the use of zone-plates [11], xenon discharge produced plasma (DPP) EUV source from Energetiq used for development of actinic full- field EUV mask blank inspection tool at MIRAI-Selete [12] and many more. One of these compact sources is a laser plasma EUV source based on a gas-puff target. Suitability of this type of target for an efficient generation of short-wavelength radiation in the EUV and SXR range was demonstrated in a variety of experiments. Employ- ing radiation, in the wavelength range from 6 to 20 nm, produced as a result of irradiation of a double-stream gas puff target with Nd:YAG laser, a direct and very efficient photo-etching of PTFE polymer [13] and micro-structuring of PMMA polymer [14] were reported. Gas-puff target EUV source was also used for studying fluorescence from Al and Si [15] and recently for a 50 nm spatial resolution imaging using diffractive optics [16,17]. Employing a double stream gas puff target allows for significant improvement in the energy conversion efficiency from IR pumping laser to EUV radiation reaching 1.6% [18]. Moreover in the ‘‘water window’’ spectral range the strong line emission was demonstrated from the 1–2 transitions in H- and He-like nitrogen ions at k = 2.478 nm and 2.879 nm, respectively using 5 J energy per pulse Nd:glass laser [19] or recently in a very compact, table-top setup employing much smaller Nd:YAG laser, 0.74 J energy per pulse, [20] for plasma generation. A significant enhancement of X-ray production in the 1-keV energy range was also achieved by modi- fication of a single nozzle gas-puff target to a double-stream scheme [21]. The usability and applications of gas puff targets are widespread. It was already demonstrated that elongated gas puff target can be also useful in X-ray laser development [22,23], extreme ultraviolet amplification in plasma [24] and HHG [25]. For some applications such as a HHG particular nozzle geome- try might be more beneficial than other. An extended gas density profile, formed by an elongated nozzle, might be beneficial, since it provides longer optical path for femto-second, intense laser 0168-583X/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2012.01.029 ⇑ Corresponding author. Tel.: +48 (22) 6839540; fax: +48 (22) 6668950. E-mail address: wachulak@gmail.com (P.W. Wachulak). Nuclear Instruments and Methods in Physics Research B 276 (2012) 38–43 Contents lists available at SciVerse ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb