Efficient soft x-ray sources from laser-irradiated gold foam targets with well-controlled impurities

Abstract

As an important x-ray source, enhancement of x-ray emissions from laser-produced plasmas is significant for various applications. Due to less expanding kinetic loss, gold foam with low initial density can have an enhanced x-ray conversion efficiency compared with solid-density gold. However, low-Z impurities within gold foam targets will diminish the enhancement remarkably, and should be tightly controlled. This paper presents an experimental study of a high brightness laser plasma soft x-ray source, based on a 0.36 g cm −3 gold foam target with negligible impurities irradiated by nanosecond laser pulses with power density around 3 × 10 14 W cm −2 at the Shenguang II laser facility. A conversion efficiency, from multi-eV to multi-keV, of 51.2% is achieved in the x-ray emissions-about 21% relative enhancement compared with a solid-density gold target, and the highest conversion efficiency for Au foam planar targets yet. Good agreement has been achieved between the semi-analytical model prediction and the experimental results.

Amplified spontaneous emission in the extreme ultraviolet by expanding xenon clusters

“…Our work closely connects to optical-laser driven table-top soft x-ray lasers and plasma generated x-ray sources [21][22][23]. In this field, much focus lies on the target design-structured targets on the nanoscale, such as nanowire arrays [24,25], foams [26], nanoparticle targeted surfaces [27,28], and clusters [29][30][31][32][33] can exhibit enhanced emission features. The understanding of the plasma evolution of such sources is, however, crucial to the gain and emission characteristics of these sources.…”

Dynamics of Laser Produced Plasma From Foam Targets for Future Nanolithography Devices and X-Ray Sources

“…Currently, some research related to the laser produced low-density tin plasma show that the complex double pulse laser scheme is expected to be replaced by using low-density foam targets in the future [26][27][28] . In addition, low density foam targets have been demonstrated to have higher x-ray radiation than solid targets in reports of the laser produced Au 23,29,30 , Cu 31 , V 31 , Ti 32 , Ca 33 , Bi 34 , and cellulose triacetate 20 plasma. Thus, low density foam targets are expected to be the most suitable candidates for the efficient LPP EUV and x-ray sources 20 .…”

“…This phenomenon can also be reflected to a certain extent from the lower and wider TOF signal of the foam Ni shown in Figure 2. These characteristics of foam Ni exhibited the so-called volumetric heating effect and a higher laser energy absorption as the laser energy increased 20,22,23,33 . Therefore, the saturation behavior of total charge was more obvious for solid Ni.…”

“…It is well known that the laser can only propagate in the plasma below the critical electron density. During the interaction between laser and plasma, an ionization wave and a rarefaction wave will be created in the conduction zone and the interface between the plasma and vacuum, respectively 20,23 . If the velocity of ionization wave propagating into the bulk target is higher than that of sound in the already heated matter, significant hydrodynamic motion will not be generated in spite of pressure gradients are very large at the position of heat front 20 .…”

“…If the velocity of ionization wave propagating into the bulk target is higher than that of sound in the already heated matter, significant hydrodynamic motion will not be generated in spite of pressure gradients are very large at the position of heat front 20 . Various studies 20,23,30 related to laser produced underdense target (the ionized electron density lower than the laser critical density) plasma pointed out that the ionization wave generated by laser ablating under-dense target is supersonic and the rarefaction wave is subsonic. In the case of under-dense plasma, no hydrodynamic motion of the dense plasma occurs because of the supersonic laser heating, resulting in no hydrodynamic shock wave generated.…”