A remote optical technique of measuring distance and thickness is described which relies on a measurement of the time a laser beam deflected at a definite speed takes to travel from a starting point on a reference plane to a final point on the object. Its significant features are high measuring speed, high resolution, flexibility with regard to measurement range and distance between reference plane and probe, insensitivity to surface properties of the object, and rugged design. It is, therefore, suitable for a large variety of applications, especially in industrial metrology.

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A single mode He-Ne laser has been frequency stabilised with a relative frequency stability of 10 -'~ and an absolute accuracy of 10-'. The reference frequency is derived from a Ne-absorption cell in an alternating magnetic field. Theoretical analysis and experiments show that this high frequency stability can be achieved only with certain time-dependent functions of the alternating field and with the proper choice of the operating parameters of the laser and absorption tube.

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Übersicht: Die vorliegende theoretische Arbeit befaßt sich eingehend mit den Modulationseigenschaften des Frequenznormals, das zur Frequenzstabilisierung eines Gaslagers verwendet wird. Es wird eine sinusförmige Zeemanmodulation der Absorptionsprofile vorausgesetzt und die resultierende Modulation des Laserstrahles analysiert. Die Analyse ergibt ein Frequenzspektrum mit sin-und cos-Komponenten und deren Oberwellen. Die sin-Komponente, die die größte Amplitude hat und mit Phase und Amplitude die Lage der Laserfrequenz bestimmt, wird zusammen mit der cos-Komponente ausgesiebt. Die cos-Komponente beeinträchtigt die Frequenzeinstellung nicht, da sie bei Annäherung an die Sollfrequenz VQ viel schneller gegen Null geht als die sin-Komponente.This theoretical paper discusses in detail the modulation properties of the frequency standard used for stabilizing the frequency of a gas laser. A sinusoidal Zeeman modulation of the absorption profiles is presumed and the resultant modulation of the laser beam analyzed. This results in a frequency spectrum with sine and cosine components and their harmonics. The sine component that has the highest amplitude and determines the position of the laser frequency with phase and amplitude, is selected together with the cosine component. The latter will not adversely affect the frequency control since it goes towards zero at a much higher rate than the sine component, as the nominal frequency t'o is approached.Für die Dokumentation: Frequenzstabilisation / Gaslaser / äußeres Frequenznormal im magnetischen Wechselfeld