Cryostat comprising: a coolant reservoir for storing liquid coolant ; and a sample observation unit for observing characteristics of a sample ; wherein the coolant reservoir comprises a vessel enclosing a storage volume with walls of the vessel being thermally insulated with a thermal reservoir insulation layer such as to enable storing liquid coolant at temperatures below 150 K; wherein the sample observation unit comprises: a tube having tube walls enclosing a tube volume including an observation volume ; a thermal tube insulation layer ; and a window arrangement ; wherein the tube is open at a distal end and at a proximal end ; wherein the distal end of the tube is arranged within the storage volume of the coolant reservoir; wherein the tube has two lateral openings in its tube walls at opposing sides with regards to the observation volume; wherein the tube walls are covered at their external side with the thermal tube insulation layer; wherein the thermal tube insulation layer has two openings adjacent to the openings in the tube walls, and wherein the window arrangement comprises two opposing panes , each pane being arranged at one of the openings in the thermal insulation layer, the panes being transparent to light of a laser beam . a coolant reservoir for storing liquid coolant ; and a sample observation unit for observing characteristics of a sample ; wherein the coolant reservoir comprises a vessel enclosing a storage volume with walls of the vessel being thermally insulated with a thermal reservoir insulation layer such as to enable storing liquid coolant at temperatures below 150 K; wherein the sample observation unit comprises: a tube having tube walls enclosing a tube volume including an observation volume ; a thermal tube insulation layer ; and a window arrangement ; wherein the tube is open at a distal end and at a proximal end ; wherein the distal end of the tube is arranged within the storage volume of the coolant reservoir; wherein the tube has two lateral openings in its tube walls at opposing sides with regards to the observation volume; wherein the tube walls are covered at their external side with the thermal tube insulation layer; wherein the thermal tube insulation layer has two openings adjacent to the openings in the tube walls, and wherein the window arrangement comprises two opposing panes , each pane being arranged at one of the openings in the thermal insulation layer, the panes being transparent to light of a laser beam . a tube having tube walls enclosing a tube volume including an observation volume ; a thermal tube insulation layer ; and a window arrangement ; wherein the tube is open at a distal end and at a proximal end ; wherein the distal end of the tube is arranged within the storage volume of the coolant reservoir; wherein the tube has two lateral openings in its tube walls at opposing sides with regards to the observation volume; wherein the tube walls are covered at their external side with the thermal tube insulation layer; wherein the thermal tube insulation layer has two openings adjacent to the openings in the tube walls, and wherein the window arrangement comprises two opposing panes , each pane being arranged at one of the openings in the thermal insulation layer, the panes being transparent to light of a laser beam . <EOS>