We present transport measurements in a quasi-1D system of surface electrons on liquid helium confined in a 101-µm long and 5-µm wide microchannel where an electrostatic potential with periodicity of 1-µm along the channel is introduced. In particular, we investigate the influence of such a potential on the nonlinear transport of quasi-1D Wigner Solid (WS) by varying the amplitude of the periodic potential in a wide range. At zero and small values of amplitude, quasi-1D WS in microchannel shows expected features such as the Bragg-Cherenkov scattering of ripplons and reentrant melting. As the amplitude of potential increases, the above features are strongly suppressed. This behavior suggests loss of the long-range positional order in the electron system, which is reminiscent of the re-entrant melting behaviour due to the lateral confinement of WS in the channel.

We propose a new scheme of attosecond pulse generation by starting from a narrow-band transform-limited highpower solid-state laser and phase lock the fundamental and its first four cascaded harmonics generated by the second-order nonlinear optical processes. The relative phase among the optical fields of the harmonics can be maintained a constant at least for thousands of nanosecond pulses. The worst-case relative phase fluctuation is 0.04π rad. It is shown that sub-single-cycle (∼ 0.37 cycle) sub-femtosecond (360 attosecond) pulses with carrier-envelope phase (CEP) control can be generated in this manner. The peak intensity of each pulse exceeds 10 14 W/cm 2 when it is focused to a spot size of 20 μm. We also demonstrate synthesis of square and saw-tooth waveforms. Correlation signal, a.u. 1 2 3 0 2 4 8 6 Time delay, fs CEP = 0 4 2 0 -2 -4 1 0 -1 The electric field synthesized waveform retrieving by the method of shaper-assistant linear cross-correlation at CEP = 0. The inset figures show the simulation of electric field waveform in black solid line and pulse envelope in blue dash line

We present a new study of the nonlinear transport of a two-dimensional electron crystal on the surface of liquid helium confined in a 10-µm-wide channel in which the effective length of the crystal can be varied from 10 to 215 µm. At low driving voltages, the moving electron crystal is strongly coupled to deformation of the liquid surface arising from resonant excitation of surface capillary waves, ripplons, while at higher driving voltages the crystal decouples from the deformation. We find strong dependence of the decoupling threshold of the driving electric field acting on the electrons, on the size of the crystal. In particular, the threshold electric field significantly decreases when the length of the crystal becomes shorter than 25 µm. We explain this effect as arising from weakening of surface deformations due to radiative loss of resonantly-excited ripplons from an electron crystal of finite size, and we account for the observed effect using an instructive analytical model.

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We study the transport of surface electrons on superfluid helium through a microchannel structure in which the charge flow splits into two branches, one flowing straight and one turned at 90 degrees. According to Ohms law, an equal number of charges should flow into each branch. However, when the electrons are dressed by surface excitations (ripplons) to form polaron-like particles with sufficiently large effective mass, all the charge follows the straight path due to momentum conservation. This surface-wave induced transport is analogous to the motion of electrons coupled to surface acoustic waves in semiconductor 2DEGs.