Revealing the second harmonic generation in a femtosecond laser-driven cluster-based plasma by analyzing shapes of Ar XVII spectral lines

Oks, E.*; Dalimier, E.*; Faenov, A.*; Pikuz, T.*; Fukuda, Yuji; Andreev, A.*; Koga, J. K.; Sakaki, Hironao; Kotaki, Hideyuki; Pirozhkov, A. S.; et al.

Optics Express (Internet), 23(25), p.31991 - 32005, 2015/12

https://doi.org/10.1364/OE.23.031991

We present experiments dealing with a femtosecond laser-driven cluster-based plasma, where by analyzing the nonlinear phenomenon of satellites of spectral lines of Ar XVII, we revealed the nonlinear phenomenon of the generation of the second harmonic of the laser frequency. For performing this analysis we developed new results in the theory of satellites of spectral lines. From such lineshape analysis we found, in particular, that the efficiency of converting the short (40 fs) intense (310 W/cm) incident laser light into the second harmonic was 2%. This result is in the excellent agreement with the 2-Dimensional Particle-In-Cell (2D PIC) simulation that we also performed. There is also an order of magnitude agreement between the thresholds for the SHG found from the line shape analysis and from the 2D PIC simulations.

3D visualization of XFEL beam focusing properties using LiF crystal X-ray detector

Pikuz, T.*; Faenov, A.*; Matsuoka, Takeshi*; Matsuyama, Satoshi*; Yamauchi, Kazuto*; Ozaki, Narimasa*; Albertazzi, B.*; Inubushi, Yuichi*; Yabashi, Makina*; Tono, Kensuke*; et al.

Scientific Reports (Internet), 5, p.17713_1 - 17713_10, 2015/12

https://doi.org/10.1038/srep17713

The Observation of a transient surface morphology in the femtosecond laser ablation process by using the soft X-ray laser probe

Hasegawa, Noboru; Nishikino, Masaharu; Tomita, Takuro*; Onishi, Naofumi*; Ito, Atsushi*; Eyama, Tsuyoshi*; Kakimoto, Naoya*; Izutsu, Rui*; Minami, Yasuo*; Baba, Motoyoshi*; et al.

X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.95890A_1 - 95890A_8, 2015/09

https://doi.org/10.1117/12.2186744

We have improved a soft X-ray laser (SXRL) interferometer synchronized with a Ti:Sapphire laser pulse to observe the single-shot imaging of the nano-scaled structure dynamics of the laser induced materials. By the precise imaging optics and double time fiducial system having been installed, the lateral resolution on the sample surface and the precision of the temporal synchronization between the SXRL and Ti:Sapphire laser pulses were improved to be 700 nm and 2 ps, respectively. By using this system, the initial stage (before 200 ps) of the ablation process of the Pt surface pumped by 80 fs Ti:Sapphire laser pulse was observed by the comparison between the soft X-ray reflective image and interferogram. We have succeeded in the direct observation of the unique ablation process around the ablation threshold such as the rapid increase of the surface roughness and surface vibration.

Low electron temperature in ablating materials formed by picosecond soft X-ray laser pulses

Ishino, Masahiko; Hasegawa, Noboru; Nishikino, Masaharu; Pikuz, T.*; Skobelev, I. Y.*; Faenov, A.*; Inogamov, N.*; Kawachi, Tetsuya; Yamagiwa, Mitsuru

X-Ray Lasers and Coherent X-Ray Sources; Development and Applications XI (Proceedings of SPIE, Vol.9589), p.958904_1 - 958904_6, 2015/09

https://doi.org/10.1117/12.2186053

To study the ablation process induced by the soft X-ray laser pulse, we investigated the electron temperature of the ablating material. Focused soft X-ray laser pulses having a wavelength of 13.9 nm and duration of 7 ps were irradiated onto target surfaces, and we observed the optical emission from surfaces by use of an optical camera. On target surfaces, we could confirm damage structures, but no emission signal in the visible spectral range during ablation could be observed. Then, we estimated the electron temperature in the ablating matter, and we estimated the electron temperature to be lower than 1 eV and the process duration was shorter than 1000 ps. This result is in good accordance with the theoretical prediction. Our investigation implies that the spallative ablation occurs in the low electron temperature region of a non-equilibrium state of warm dense matter. We will present the current state of our eperimental results.

Laser-driven multi-charged heavy ion beam acceleration

Nishiuchi, Mamiko; Sakaki, Hironao; Esirkepov, T. Z.; Nishio, Katsuhisa; Pikuz, T. A.*; Faenov, A. Ya.*; Pirozhkov, A. S.; Sagisaka, Akito; Ogura, Koichi; Kanasaki, Masato; et al.

Research Using Extreme Light; Entering New Frontiers with Petawatt-Class Lasers II (Proceedings of SPIE, Vol.9515), p.95151D_1 - 95151D_4, 2015/06

https://doi.org/10.1117/12.2179204

Experimental demonstration of multi-charged heavy ion acceleration from the interaction between the ultra-intense short pulse laser system and the metal target is presented. The laser pulse of 10 J laser energy, 36 fs pulse width, and the contrast level of 10 from 200 TW class Ti:sapphire J-KAREN laser system at JAEA is used in the experiment. Almost fully stripped Fe ions accelerated up to 0.9 GeV are demonstrated. This is achieved by the high intensity laser field of 10Wcm interacting with the solid density target. The demonstrated iron ions with high charge to mass ratio (Q/M) is difficult to be achieved by the conventional heavy ion source technique in the accelerators.

Development of an apparatus for characterization of cluster-gas targets for laser-driven particle accelerations

Jinno, Satoshi; Fukuda, Yuji; Sakaki, Hironao; Yogo, Akifumi; Kanasaki, Masato; Kondo, Kiminori; Faenov, A. Ya.; Skobelev, I. Yu.*; Pikuz, T. A.; Boldarev, A. S.*; et al.

Progress in Ultrafast Intense Laser Science XI; Springer Series in Chemical Physics, Vol.109, p.215 - 233, 2015/00

https://doi.org/10.1007/978-3-319-06731-5_10

Clusters formed in supersonic gas expansion through a three-staged conical nozzle have been verified by measuring the angular distribution of the light scattered from cluster target. The size distirbutions of the clusters are calculated based on the Mie theory. The reliability of the size measurement is verified to be an experimental error of 10% using standard particles. The mean sizes of CO clusters for the cases of CO/H and CO/He mixed-gas targets are estimated to be 0.26 m and 0.22 m, respectively. For the CO/H, the cluster density is estimated to be 5.5 clusters/cm by measuring the attenuation of the laser beam intensity. Furthermore, total gas density profiles are obtained via the Abel inversion from the phase shift of the light passing through the target using an interferometer. The variation of the cluster mass fraction along the radial direction of the target is almost constant, which is consistent with a Boldarev's model.

Very low electron temperature in warm dense matter formed by focused picosecond soft X-ray laser pulses

Ishino, Masahiko; Hasegawa, Noboru; Nishikino, Masaharu; Pikuz, T. A.*; Skobelev, I. Y.*; Faenov, A.*; Inogamov, N. A.*; Kawachi, Tetsuya; Yamagiwa, Mitsuru

Journal of Applied Physics, 116(18), p.183302_1 - 183302_6, 2014/11

https://doi.org/10.1063/1.4901943

We investigated the optical emission from the ablating surfaces induced by the irradiations of soft X-ray laser (SXRL) pulses with the aim of estimation of the maximum electron temperature. No emission signal in the spectral range of 400-800 nm could be observed despite the formation of damage structures on the target surfaces. Hence, we estimated an upper limit for the electron temperature of 0.4-0.7 eV for the process duration of 100-1000 ps. Our results imply that the ablation and/or surface modification by the SXRL is not accompanied by plasma formation but is induced by thermo-mechanical pressure, which is so called a spallative ablation. This spallative ablation process occurs in the low electron temperature region of a non-equilibrium state of warm dense matter.

Surface nano-structuring produced by spallation of metal irradiated by an ultrashort laser pulse

Inogamov, N. A.*; Zhakhovsky, V. V.*; Ashitkov, S. I.*; Emirov, Y. N.*; Faenov, A. Y.*; Pikuz, T. A.*; Ishino, Masahiko; Kando, Masaki; Hasegawa, Noboru; Nishikino, Masaharu; et al.

Journal of Physics; Conference Series, 500(11), p.112070_1 - 112070_6, 2014/05

https://doi.org/10.1088/1742-6596/500/11/112070

The mechanism of formation and geometry of surface structures are discussed for the case of single pulse acting on a well-polished metal surface. We demonstrate that the complex surface nano-structures are formed after laser irradiation due to the thermomechanical spallation of ultrathin surface layer of melt. Spallation is accompanied by a strong foaming of melt followed by breaking of the foam. After several nanoseconds the foam remnants freeze up with formation of complex nano-structures on a target surface.

Detailed analysis of hollow ions spectra from dense matter pumped by X-ray emission of relativistic laser plasma

Hansen, S. B.*; Colgan, J.*; Faenov, A. Ya.*; Abdallah, J. Jr.*; Pikuz, S. A. Jr.*; Skobelev, I. Yu.*; Wagenaars, E.*; Booth, N.*; Culfa, O.*; Dance, R. J.*; et al.

Physics of Plasmas, 21(3), p.031213_1 - 031213_9, 2014/03

https://doi.org/10.1063/1.4865227

Analysis of Mg spectral features produced by irradiations of laser pulses with different contrast and pulse durations

Stafford, A.*; Safronova, A. S.*; Safronova, U. I.*; Kantsyrev, V. L.*; Faenov, A. Ya.; Wiewior, P.*; Weller, M. E.*; Shrestha, I.*; Shlyaptseva, V. V.*; Paudel, Y.*

Journal of Physics B; Atomic, Molecular and Optical Physics, 47, p.065001_1 - 065001_10, 2014/02

https://doi.org/10.1088/0953-4075/47/6/065001