A helium cryostat with pumping of 3He vapors for optical investigations

The construction of a helium cryostat with pumping of 3He vapors designed for optical measurements with a high spatial resolution in the temperature range 0.45–4.20 K. The cryostat is equipped with four windows made from fused silica. A studied sample is mounted inside a reservoir filled with liquid 3He in a holder minimizing the influence of both vibrations and thermal drifts and can stay in the chamber at T = 0.45 K for >20 h. The cryostat was used to study photoluminescence of GaAs/AlGaAs semiconductor heterostructures. It was revealed that, in a structure with two tunnel-coupled GaAs quantum wells with a width of 120 Å, the threshold pumping power required for the appearance of a narrow spectral line, which corresponds to the Bose condensate of spatially indirect dipolar excitons, decreases by a factor of 6, as the temperature falls from 1.50 to 0.45 K. In a sample with a single wide (250 Å) GaAs quantum well, the distribution patterns of the luminescence of dipolar excitons inside a 5-µm circular potential trap were obtained at T = 0.45 K. The spatial resolution of the distributions is no worse than 1.5 µm.