We report on the first successful proof-of-principle experiment to manipulate laser-matter interactions on microscales using highly ordered Si microwire arrays. The interaction of a high-contrast short-pulse laser with a flat target via periodic Si microwires yields a substantial enhancement in both the total and cutoff energies of the produced electron beam. The self-generated electric and magnetic fields behave as an electromagnetic lens that confines and guides electrons between the microwires as they acquire relativistic energies via direct laser acceleration. DOI: 10.1103/PhysRevLett.116.085002 Laser-matter interactions at relativistic intensities have exhibited many interesting physical processes. These include the acceleration of electrons [1][2][3][4], protons, and heavy ions [5][6][7], the creation of electron-positron jets [8][9][10], and attosecond pulse generation [11,12]. The investigation of ultrashort pulse lasers interacting with initially soliddensity matter has been mainly focused on flat targets, with little or no control over the interaction. Recently the focus has shifted toward using advanced targets with the aim of increasing laser beam absorption and subsequent energy partition among various plasma species. Structured interfaces including nanoparticles [13], snowflakes [14], and nanospheres [15] have been reported to enhance laser absorption and proton acceleration, and the trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowires resulted in volumetric heating of dense matter into a new ultrahot plasma regime [16]. Another proposal addressed the potential for prescribing geometrical structures on the front of a target to greatly enhance the yield of high-energy electrons while simultaneously confining the emission to narrow angular cones [17].Microengineering laser plasma interactions, at intensities above the material damage threshold, has not been extensively explored. The main reason is that the amplified short pulses are inherently preceded by nanosecond-scale pedestals [18]. This departure from an ideal pulse can substantially modify or destroy any guiding features before the arrival of the intense portion of the pulse.Laser-pulse cleaning techniques are now being employed to significantly minimize unwanted prepulse and pedestals. For example, Ti:sapphire-based short-pulse high-intensity lasers routinely use a cross-polarized wave generation technique to achieve a contrast of at least 10 10 on the nanosecond time scale [19]. The manufacturing of advanced micro-and nanostructures has been the domain of specialized scientific disciplines such as nanoelectronics [20], microfluidics [21], and photovoltaics [22]. Microstructures with features as small as 200 nm can now be easily manufactured by nonexperts using commercially available 3D direct laser writing instruments [23]. Furthermore, 3D large-scale simulations with enough spatial and temporal resolution to capture the details of the interaction are now possible thanks to recent advances in massiv...

We present an experimental demonstration of the efficient acceleration of electrons beyond 60 MeV using micro-channel plasma targets. We employed a high-contrast, 2.5 J, 32 fs short pulse laser interacting with a 5 m inner diameter, 300 m long microchannel plasma target. The micro-channel was aligned to be collinear with the incident laser pulse, confining the majority of the laser energy within the channel. The measured electron spectrum showed a large increase of the cut-off energy and slope temperature when compared to that from a 2 m flat Copper target, with the cutoff energy enhanced by over 2.6 times and the total energy in electrons >5 MeV enhanced by over 10 times. Three-dimensional particle-in-cell simulations confirm efficient direct laser acceleration enabled by the novel structure as the dominant acceleration mechanism for the high energy electrons. The simulations further reveal the guiding effect of the channel that successfully explains preferential acceleration on the laser/channel axis observed in experiments. Finally, systematic simulations provide scalings for the energy and charge of the electron pulses. Our results show that the micro-channel plasma target is a promising electron source for applications such as ion acceleration, Bremsstrahlung X-ray radiation, and THZ generation.

High intensity laser-plasma interactions produce a wide array of energetic particles and beams with promising applications. Unfortunately, high repetition rate and high average power requirements for many applications are not satis ed by the lasers, optics, targets, and diagnostics currently employed. Here, we address the need for high repetition rate targets and optics through the use of liquids. A novel nozzle assembly is used to generate high-velocity, laminarowing liquid microjets which are compatible with a low-vacuum environment, generate li le to no debris, and exhibit precise positional and dimensional tolerances. Jets, droplets, submicron thick sheets, and other exotic con gurations are characterized with pump-probe shadowgraphy to evaluate their use as targets. To demonstrate a high repetition rate, consumable, liquid optical element, we present a plasma mirror created by a submicron thick liquid sheet. is plasma mirror provides etalon-like anti-re ection properties in the low-eld of 0.1% and high re ectivity as a plasma, 69%, at a repetition rate of 1 kHz. Practical considerations of uid compatibility, in-vacuum operation, and estimates of maximum repetition rate in excess of 10 kHz are addressed. e targets and optics presented here enable the use of relativistically intense lasers at high average power and make possible many long proposed applications. . All diode-pumped, highrepetition-rate advanced petawa laser system (hapls).

Articles you may be interested inCooperative molecular field effect and induced orientational ordering effect in polar liquid crystalline films on metalsWe have developed a new type of target for intense laser-matter experiments that offers significant advantages over those currently in use. The targets consist of a liquid crystal film freely suspended within a metal frame. They can be formed rapidly on-demand with thicknesses ranging from nanometers to micrometers, where the particular value is determined by the liquid crystal temperature and initial volume as well as by the frame geometry. The liquid crystal used for this work, 8CB (4 0 -octyl-4-cyanobiphenyl), has a vapor pressure below 10 À6 Torr, so films made at atmospheric pressure maintain their initial thickness after pumping to high vacuum. Additionally, the volume per film is such that each target costs significantly less than one cent to produce. The mechanism of film formation and relevant physics of liquid crystals are described, as well as ion acceleration data from the first shots on liquid crystal film targets at the Ohio State University Scarlet laser facility. V C 2014 AIP Publishing LLC. [http://dx.

We report on the recently completed 400 TW upgrade to the Scarlet laser at The Ohio State University. Scarlet is a Ti:sapphire-based ultrashort pulse system that delivers >10  J in 30 fs pulses to a 2 μm full width at half-maximum focal spot, resulting in intensities exceeding 5×10²¹ W/cm². The laser fires at a repetition rate of once per minute and is equipped with a suite of on-demand and on-shot diagnostics detailed here, allowing for rapid collection of experimental statistics. As part of the upgrade, the entire laser system has been redesigned to facilitate consistent, characterized high intensity data collection at high repetition rates. The design and functionality of the laser and target chambers are described along with initial data from commissioning experimental shots.