In this work, the time development of plasmas produced by interaction of laser pulses, with a nitrogen gas, was investigated. The interaction took place inside a small portion of dense nitrogen gas injected temporarily into a chamber filled with the gas under low pressure. High-temperature plasmas produced directly by the laser pulse were a source of soft x rays and charged particles, ionizing and exciting the surrounding gas. In this way, low-temperature plasmas were produced. The formation of high-temperature plasmas was studied using soft x-ray spectroscopy and x-ray streak imaging. Low-temperature plasmas formed at various distances from the laser focus were investigated using an optical streak camera. Interpretation of the experimental data was supported by numerical modeling of the laser-produced plasma hydrodynamics. It was concluded that depending on the distance from the focal spot, the formation of the low-temperature plasmas was dominated by ion streams or by soft x-ray radiation.

Low-temperature plasma production is possible as a result of photoionization using high-intensity extreme ultraviolet (EUV) and soft X-ray (SXR) pulses. Plasma of this type is also present in outer space, e.g., aurora borealis. It also occurs when high-velocity objects enter the atmosphere, during which period high temperatures can be produced locally by friction. Low-temperature plasma is also formed in an ambient gas surrounding the hot laser-produced plasma (LPP). In this work, a special system has been prepared for investigation of this type of plasma. The LPP was created inside a chamber filled with a gas under a low pressure, of the order of 1–50 mbar, by a laser pulse (3–9 J, 1–8 ns) focused onto a gas puff target. In such a case, the SXR/EUV radiation emitted from the LPP was partially absorbed in the low-density gas. In this case, high- and low-temperature plasmas (T e ~100 eV and ~1 eV, respectively) were created locally in the chamber. Investigation of the EUV-induced plasmas was performed mainly using spectral methods in ultraviolet/visible (UV/VIS) light. The measurements were performed using an echelle spectrometer, and additionally, spatial–temporal measurements were performed using an optical streak camera. Spectral analysis was supported by the PGOPHER numerical code.

The PolFEL free electron laser, currently under construction at the National Centre for Nuclear Research in Poland, will generate a beam of coherent electromagnetic radiation in the ultraviolet (UV) spectral range with a wavelength of about 150 nm to 300 nm, in the form of several hundred fs pulses, energy up to 50 μJ, and repetition rate of 50 kHz. Vacuum ultraviolet (VUV) radiation beam in the wavelength range from 50 nm to 100 nm will be obtained by selecting the third harmonic using an absorption filter. The optical system of the UV/VUV beamline consists of two plane M1 and M2 mirrors and one focusing ellipsoidal M3 mirror. The radiation produced in the laser hits on the M1 mirror at a grazing incidence angle of 5°. After reflection from the M1 mirror, the beam falls on the M2 mirror at an angle of 17°, which directs the beam to the ellipsoidal M3 mirror, focusing the beam at the image plane at the second focal point of the ellipsoid. The M1 mirror is placed behind the 3 m-thick concrete wall in a hutch separated from the experimental hall by a 1.6 m-thick concrete wall. The optical properties of the beamline were tested by ray-tracing simulations using the RAY-UI software, the results of which are presented in the paper.

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