Calculated beam size as a function of propagation distance. Plasma channels are indicated as shaded regions. (a) Matched guiding (solid black) for the case of r 0 = r m = 18 μm and mismatched guiding (dotted-dashed red) for the case of r 0 = 18 μm and r m = 41 μm. Laser is focused at the entrance of plasma channel, z = 0. (b) Laser is focused at z = 0 (dotted-dashed red) and z = 5 (dashed blue) for the mismatched guiding with r 0 = 18 μm and r m = 41 μm.
The experimental layout. The laser beam was focused onto a capillary waveguide using a 2 m focal length off-axis parabolic mirror. The output laser pulse was attenuated with two uncoated wedges and weakly focused onto the optical spectrometer.
Schematic of the capillary (grey rectangle) and gas inlets (blue lines). Normalized on-axis plasma density as a function of propagation distance for two different profiles (I) and (II). The effects of two profiles are investigated in Sec. VI C .
PIC simulation result for a laser of r 0 = 18 μm, r m = 41 μm, a 0 = 1.2, focused 4.8 mm into a 33 mm long capillary. (a) Peak accelerating field (solid black), laser energy (dashed black), and (red), showing the amount of redshift as functions of propagation distance in the plasma channel. (b) Laser spectra before the channel (solid blue), after first E max peak (dashed green) and at the exit of the channel (dotted-dashed red). (c) The ratio of energy in the transverse and the longitudinal fields as defined by Eq. (7) .
(a) Normalized input and output optical spectra for input and 1.3. Each line is an average of ∼15 shots. (b) as a function of for n 0 = 1.5 × 1018/cm3. ΔR from the experiment and simulations are shown. (c) Measured optical spectra for for the case of . Each line is an average of ∼15 shots. (d) ΔR as a function of fora 0 = 1.0 and 1.2. ΔR from the experiment and simulations are shown. Simulations were performed using measured a 0, measured temporal profile, and linear density ramps [profile (II)] as shown in Fig. 3 .
Experimental results from a compressor scan. Pulse duration and ΔR as a function of compressor positions. The vertical black dotted line and the red dotted-dashed line indicate where pulses shown in Figs. 7(a) and 7(b) were measured.
Experimental and simulated results from a compressor scan. (a) and (b) Temporal pulse shapes measured by GRENOUILLE at compressor positions −0.19 mm and 0.11 mm. The pulses travel to the left in the graphs and Gaussian distributions are shown for reference. (c) Experimentally measured spectra with a steep intensity rise at −0.20 mm and a gentle rise at 0.10 mm. (d) Simulated spectra using combinations of positive and negative chirps with the two intensity profiles (a) and (b).
(a) Measured optical spectra for a 0 = 1.2, Z f = 0.8 mm (solid black), and Z f = 4.8 mm (dotted-dashed red). (b) ΔR as a function of Z f. The larger Z f indicates the laser is focused further downstream of the capillary entrance.
Transverse intensity profiles at focus, 2 mm, 4 mm, and 6 mm from the focus. (a) Measured intensity profiles using a CCD camera. (b) ZEMAX simulated intensity profiles based on measured wavefront and intensity using a wavefront sensor. (c) ZEMAX simulated intensity profiles with simplified wavefront and uniform intensity profile.
Simulated E max and ΔR as a function of propagation distance for fundamental Gaussian and higher order LG beams.
Laser field and wakefield profiles for Gaussian and LG beams at z = 26 mm, approximately from the second excitation peak. The top row shows the fields for the Gaussian beam and the bottom row shows the fields for the LG beam. The laser pulse propagates toward +z. (a) and (e) are longitudinally integrated laser intensity, (b) and (f) are laser intensity, (c) and (g) are E z/E 0, and (d) and (h) are .
Measure of redshift, ΔR, as a function of vacuum for plasma density scans at a 0 = 1.0 and 1.2, and laser energy scan at n 0 = 1.5 × 1018/cm3 (black). Simulated results for a 0 = 1.0, 1.2, and 1.3 for n 0 = 1.5 × 1018/cm3, n 0 = 1.2 × 1018/cm3, and n 0 = 0.75–1.5 × 1018/cm3 for a 0 = 1.2 (red) are also shown.
Estimates of averaged wakefield amplitudes in the experiments based on ΔR. Calculated for the a 0 and n 0 scans (data set 1 and 2) are plotted. The density scans varied for a 0= 1.0 and 1.2. The energy scan varied for .
Parameters for the experimental data set. The laser energy was varied for set 1. The hydrogen gas pressure was varied for set 2. The separation of the compressor gratings was varied for set 3. The capillary position with respect to the vacuum laser focus was varied for set 4.
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