  Solid-state high harmonic generation spectroscopy (sHHG) 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 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.
