Infrared technique: period 1934 – 1959
Infrared river barrage
In 1934, the Commission for Physical Armorment of the Ministry of War was requested to conduct experiments with invisible rays. They wanted a means of detection to be able to observe enemy ships by night and in mist. This could activate the river barriers with ground mines. In 1936, the first tests were taken with an infrared flashing light (see also: “Background: what is infrared?” at the bottom of this page). The receiver used a so-called talloid cell.
A period of trials and improvements followed between 1937 and 1939. Among other things, experiments were done with multiple infrared beams across the river so that the right mine of the barrier would explode at the right time. In 1939, the Artillery Establishments commissioned the manufacturing of the system by NV Nederlandsche Instrumentenfabriek Waldorp in The Hague. The system was used by the Corps Pontoon laying and Torpedoists. In the May days of 1940, the system was used as a river barrier across the river Merwede (without connected mines).
In 1935, experiments with infrared photography were carried out for a short period for the Royal Netherlands Navy. A minor improvement in vision was observed as compared to ordinary photography in the event of a clearing.
The tests were not convincing although the importance of the invention was recognised.
In July 1938, initial tests were held with an infrared viewer developed by Philips at the end of 1937 ‘to see in the dark’. The surroundings were illuminated with a spotlight with a special glass window that emitted ‘dark light’. The viewer contained a light-amplifying electron tube. According to Philips, the system was capable to view in the dark up to 300 metres. The system would be ‘portable’ by two people.
In January 1939, Philips lent a viewer system to the Navy. They returned the viewer as its optics were not frost- and seawater resistant. In the same month, the Meetgebouw received a newer, better electron tube from Philips with enhanced contrast. Again some tests were carried out.
Early April 1939, the Philips management wrote a letter to the Minister of Defence pushing him to make a decision about the acquisition of the viewers and the lighting system. When asked, the Meetgebouw reported to the Minister that the claim of ‘300 metres’ says nothing about being able to observe ‘large or small terrain objects or standing or crawling soldiers’. The tests, which were held late at night on the Waalsdorpervlakte, were not convincing.
New tests were held on April 9, 1940. On May 3, 1940, a week before the outbreak of the German invasion, the Meetgebouw completes a technical report on the latest Philips system: The visual acuity decreases with a factor of two to three. Moreover, it is technically difficult to use filters to shield the light source in such a way that it will not be detectable: a red glow remained visible. The Meetgebouw suggests that the infrared lamp is hung high on a roof or in trees for surveillance purposes. The ‘attacker’ will ‘look carefully around in general, but only rarely up, also because in that direction the view is usually obscured by a helmet or cap.‘ Tests were conducted with such an arrangement (12 V, 50 W, 1500 lumen lamp). The conclusion was that this would be useful ‘for the security monitoring of important locations’.
Immediately after the liberation of the Netherlands, new experiments with the improved infrared viewer were carried out in 1946 – 1947. In 1948, a device for detection at night was developed using a searchlight. All the light from the visible spectrum was filtered out while maintaining the infrared spectrum. The idea was very sound, and a lot of the research was spent in optimising the design, by researching the needed filters, tubes for image conversion, types of searchlights, etc. The Royal Netherlands East Indies Army (KNIL) needed such equipment to track down people in the jungle.
After WWII, the infrared investigations for the Navy were picked up again, especially to be able to determine the detection distance to ships at sea using passive means at night. In 1947, ships at Scheveningen were detected up to a few kilometres away with infrared observation using a platinum bolometer and an old German 60 cm diameter searchlight mirror. The conclusion was that infrared scanning would work fine ashore, but on a floating platform stability issues would arise given the long processing time.
In 1957, with a self-developed highly sensitive Golay detector (wiki: Golay), the observation distance of ships was increased to 15 kilometres as was evident from experiments at Kijkduin.
In 1957, work started on the development of semiconductor bolometers and photocells based on PbSe, PbS, CdSe, and InSb.
T. Nooijen (2015), Physics Research at RVO-TNO during the early cold war, Univ. of Utrecht (pdf)