A group led by Miles Padget of the University of Glasgow has developed a laser scanner, such as LIDAR, that provides a 3D image of the environment, but allows its signals to pass through very thin glass fibres. This promises a kind of endoscope with which one can photograph through even the smallest apertures.
Padget and the team give details of their development In an unreviewed post on the arXiv prepress server. The basic idea of the system is to send a laser pulse through the glass fiber and absorb its reflection by another glass fiber. The length of time between the transmission of a pulse and its reflected echo, per millimeter, shows how far away the imaged object is. The system can still take pictures from a distance of two and a half metres.
This technique works because scientists can modulate the laser pulses very precisely. Their wave front is shaped in such a way that they focus only on one freely selectable point. In initial tests, they succeeded in scanning a total of 23,000 points five times per second and measuring the distance between them. Then a 3D image is generated on the computer.
The biggest problem with this endeavor is that the 40 cm long glass fibers disrupt the laser pulse on the way, bringing the previously innovative modulation at the tip to an unusable state. This difficulty has only been partially resolved so far. Padget and his team help by first calibrating the system: They determine what will happen to a given signal after it passes through the fibre, then calculate the interference backwards. During the actual measurement, the laser pulse is preformed so that it is the interference that distorts it into the desired signal.
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