High-Intensity Laser-Driven Oxygen Source from CW Laser-Heated Titanium Tape Targets

Abstract

The interaction of high-intensity laser pulses with solid targets can be used as a highly charged, energetic heavy ion source. Normally, intrinsic contaminants on the target surface suppress the performance of heavy ion acceleration from a high-intensity laser–target interaction, resulting in preferential proton acceleration. Here, we demonstrate that CW laser heating of 5 µm titanium tape targets can remove contaminant hydrocarbons in order to expose a thin oxide layer on the metal surface, ideal for the generation of energetic oxygen beams. This is demonstrated by irradiating the heated targets with a PW class high-power laser at an intensity of 5 × 1021 W/cm2, showing enhanced acceleration of oxygen ions with a non-thermal-like distribution. Our new scheme using a CW laser-heated Ti tape target is promising for use as a moderate repetition energetic oxygen ion source for future applications.

Metrology for sub-Rayleigh-length target positioning in ∼1022 W/cm2 laser–plasma experiments

“…The laser operated at 0.1 Hz, delivering typically several hundred full-power shots per experimental day. [26] mounted at a 45º incident angle. The observation direction of the backreflection diagnostics at 1ω is shown by the red arrow.…”

“…Fig. 1 shows the experimental scheme: the main laser pulse, the 5-to-20-μm-thick stainless steel (SUS) tape target [26] mounted 45º off-normal, and the diagnostics discussed herein:  (Front) Reflected beam footprint diagnostics (at frequencies 1ω, 2ω and 3ω);  (Front) Back-reflection diagnostics (at 1ω, the diagnostics is outside Fig. 1);  (Rear) XUV imaging spectrograph for wavelengths 17 -25 nm;  (Rear) Magnetic electron spectrometer (ESM) for 20 -100 MeV electrons;  (Rear) Two hard X-ray spectrometers (HXRS-1,2) for 0.1 -10 MeV photons;  (Front and Rear) Two soft X-ray focusing spectrometers with spatial resolution (FSSR-F and FSSR-R) for 0.7 -10 keV photons;  (Front) Three-channel Flat-Field XUV spectrograph (3FF), λ = 17 -34 nm.…”

“…Most of the existing high-intensity experiments have been carried out at laser intensities I0 ~ 10 18 to 10 21 W/cm 2 (a0 ~ 1 to 30), and only a few at I0 > 10 21 W/cm 2 [25][26][27][28][29][30][31][32][33] . New regimes of laser-matter interaction require intensities I0 ~ 10 22 W/cm 2 and higher, leading to efficient radiation-pressure-dominant ion acceleration at I0 > 10 22 W/cm 2 [34,35] , radiation damping at I0 > 3×10 23 (μm/λ) 4/3 W/cm 2 [24] , and quantum electrodynamic effects at I0 > 6×10 24 W/cm 2 [36] .…”

Diagnostics for precise target positioning in ~10^22 W/cm2 laser-plasma experiments

“…The electric field amplitude E 0 in the laser pulse defines the driving force exerted on the electrons with elementary charge e and mass m, thus identifying the relativistic regimes with a 0 >> 1. Most of the high-intensity laser-matter experiments up to date have been carried out at laser intensities I 0 ~ 10 18 to 10 21 W/cm 2 (a 0 ~ 1 to 30), and only a few at I 0 > 10 21 W/cm 2 [25][26][27][28][29]. New physical regimes of the laser-matter interaction require intensities I 0 ~ 10 22 W/cm 2 and higher, leading to an efficient radiation-pressure-dominant ion acceleration at I 0 > 10 22 W/cm 2 [30,31], radiation damping regime at I 0 > 3×10 23 (μm/λ) 4/3 W/cm 2 [24], and exhibition of pure quantum electrodynamic effects at I 0 > 6×10 24 W/cm 2 [32].…”