Christian Spielmann

Solid-state high harmonic generation (sHHG) spectroscopy is a promising technique for studying electronic structure, symmetry, and dynamics in condensed matter systems. Here, we report on the implementation of an advanced sHHG spectrometer based on a vacuum chamber and closed-cycle helium cryostat. Using an in situ temperature probe, it is demonstrated that the sample interaction region retains cryogenic temperature during the application of high-intensity femtosecond laser pulses that generate high harmonics. The presented implementation opens the door for temperature-dependent sHHG measurements down to a few Kelvin, which makes sHHG spectroscopy a new tool for studying phases of matter that emerge at low temperatures, which is particularly interesting for highly correlated materials.

In this study, the influence of hybrid speckle patterns on the contrast-to-noise ratio (CNR) and resolution in pseudo-thermal ghost imaging (PGI) was examined based on the object dimensions in the macroscopic and microscopic regimes. This research shows that an enhanced scaling of the ghost image CNR and resolution from that of the hybrid speckle pattern was observed with the increase in speckle size for a macroscopic object, compared with the use of single-size speckle patterns. For microscopic objects, the hybrid speckle pattern also offered the advantage of retrieving ghost images even if the CNR followed the same trend as the resolution. These results were verified using two different slits with the same transmitted area. In addition, the numerical analysis revealed that the interference of the hybrid speckle pattern was the major factor for a better CNR. Based on these findings, the novel hybrid speckle pattern found in this research provides a possible way for future experiments in PGI to regulate hybrid speckle patterns to obtain a better ghost image quality.