A Jones Calculus Approach to High-Order Harmonic Generation in Solids

High-order harmonics from bulk solids were first observed in 2011 by focusing an intense mid-infrared laser through a bulk crystal and detecting the harmonics in a transmission geometry. Due to birefringence and possible nonlinear effects in bulk crystal, the polarization state of the laser can change as it propagates through the crystal in this transmission geometry. This can result in harmonic signal generated with an unknown polarization of light, disrupting the signal. Alternatives to bulk crystal, such as a reflection geometry or thin films, are not always ideal – reflection geometry can introduce nonlinear reflection coefficients, while crystalline thin films can be difficult to produce and are not available for all materials. We propose Jones calculus as a new method to analyze high-order harmonics from bulk solids in a transmission geometry. We predict the laser’s polarization changes due to propagation through a bulk crystal and we show that these changes can be accounted for using a combination of wave plates. Our results indicate that linear birefringence dominates the polarization change in bulk ZnO crystals driven in the mid-IR, which allows us to neglect the effect of nonlinear propagation effects on the polarization state. After compensating for the birefringence, we observe ellipticity-dependent, rotationally sensitive features in the harmonic signal which differ from those observed in previous transmission-geometry experiments. This method increases confidence in and control of HHG measurements in bulk crystal

Flying doughnut terahertz pulses generated from semiconductor currents

The ability to manipulate the space-time structure of light waves diversifies light-matter interaction and light-driven applications. Conventionally, metasurfaces are employed to locally control the amplitude and phase of light fields by the material response and structure of small meta-atoms. However, the fixed spatial structures of metasurfaces offer limited opportunities. Here, using quantum control we introduce a new approach that enables the amplitude, sign, and even configuration of the generated light fields to be manipulated in an all-optical manner. Following this approach, we demonstrate the generation of flying doughnut terahertz (THz) pulses. We show that the single-cycle THz pulse radiated from the dynamic semiconductor ring current has an electric field structure that is azimuthally polarized and that the space- and time-resolved magnetic field has a strong, isolated longitudinal component. As a first application, we detect absorption features from ambient water vapor on the spatiotemporal structure of the measured electric fields and the calculated magnetic fields. Quantum control is a powerful and flexible route to generating any structured light pulse in the THz range, while pulse compression of cylindrical vector beams is available for very high-power magnetic-pulse generation from the mid-infrared to near UV spectral region. Pulses such as these will serve as unique probes for spectroscopy, imaging, telecommunications, and magnetic materials

Laser waveform control of extreme ultraviolet high harmonics from solids

Solid-state high-harmonic sources offer the possibility of compact, high-repetition-rate attosecond light emitters. However, the time structure of high harmonics must be characterized at the sub-cycle level. We use strong two-cycle laser pulses to directly control the time-dependent nonlinear current in single-crystal MgO, leading to the generation of extreme ultraviolet harmonics. We find that harmonics are delayed with respect to each other, yielding an atto-chirp, the value of which depends on the laser field strength. Our results provide the foundation for attosecond pulse metrology based on solid-state harmonics and a new approach to studying sub-cycle dynamics in solids

High Harmonic Generation In Zno With A High-Power Mid-Ir Opa

We generate high-order harmonics in a-cut (11-20) ZnO at a high repetition rate of 50 kHz, using the tunable mid-infrared pulses (3-4 μm wavelength) from a high-power optical parametric amplifier. For driving laser pulses with 3.8 μm central wavelength, we observe nonperturbative harmonic spectra that well exceed the material band gap. The harmonic spectra depend strongly on the orientation of the crystal with respect to the laser polarization, with odd harmonics exhibiting periodicities of π/2 for a polarization within the (11-20) crystal plane. Energy conversion efficiencies of ∼10−6 per harmonic are measured for the 9th-13th harmonics, yielding an average power of more than 0.2 μW for the 13th harmonic

High-Order Harmonic Generation In Zno Using Few-Cycle Mid-Ir Pulses Generated Via Self-Compression

We exploit nonlinear self-compression in YAG to generate sub-three-cycle, 10 μJ pulses from a 50 kHz mid-IR OPA. Efficiency and cutoff enhancement of generated high-order harmonics in ZnO relative to longer driving pulses demonstrates the potential for solid-state attosecond pulse generation through nonlinear self-compression

Spectral Broadening And Pulse Compression Of A 400 Μ J, 20 W Yb:Kgw Laser Using A Multi-Plate Medium

We investigate the potential of a multi-plate medium consisting of thin fused silica plates to generate few-cycle pulses from a moderately high energy (400 μJ) and average power (20 W) Yb:KGW laser centered at 1025 nm. By optimizing the thicknesses and positions of the plates, we mitigate the losses associated with spatial and spectral distortions that can accompany self-focusing in bulk solids. Pulses with an initial duration of ∼280 fs were compressed using chirped mirrors, after spectral broadening in a multi-plate medium consisting of 6 mm of fused silica in total, by a factor of \u3e5 to 50 fs. Further spectral broadening in a second stage also consisting of 6 mm of fused silica in total enabled compression to 18 fs with 40 μJ pulse energy, with the energy efficiency limited primarily by the geometry of the chirped mirror compressors

High Harmonic Generation In Zno From A 50 Khz Opa

We generate high-order harmonics in ZnO using a mid-IR OPA with 50 kHz repetition rate. Nonperturbative harmonic spectra beyond the band gap exhibit strong dependence on the crystal orientation with respect to the laser polarization