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.