Laser gyroscopes

A very large area of application for the glass ceramic Zerodur is the technology for modern navigation of space rockets, aircraft, and ships or the positioning of telescopes, antennas, or satellites. The negligibly small coefficient of thermal expansion and the extremely small helium permeability of the material are of particular importance for this application. 

For navigation technology the conventional electro-mechanical gyroscope is to be replaced by a system with digital analysis without mechanically moving parts. 

The advantage of Zerodur lies in the above-mentioned low permeability of the material for helium atoms which is of particular importance for 

In 2001, the so-called G ring laser gyroscope was taken into service at the Wettzell Fundamental Research Station with the purpose of precisely measuring the Earth s rotation. 

The frequency difference occurring with the normal variations in the Earth s rotation in the course of a day is 10 s out of a frequency of 300 s . To be able to record such minute differences, the sensitivity of the G ring laser gyroscope has to be more than a thousand times higher than that of normal gyroscopes used, for example, in navigation systems. 

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For a three-axis system, three triangles in mutually perpendicular planes may be used. For navigational purposes, the output of the laser gyroscope may be integrated to determine the heading of an aircraft. Laser-based navigation systems have been in use on commercial and military aircraft since the early 1980s. 

Beyond the scope of this article, Anderson explains the operation of the gyroscope in intimate detail and describes two problems that have proved most vexing to manufacturers of the rtng-laser gyroscope, namely, frequency locking at low rotation rates and the bias effect. Improvements In this instrument are expected in the relatively near future heeause of what scientists have recently learned pertaining to the phenomenon of optical phase conjugation. 

An important application for Zerodur is laser gyroscopes as will be described in Sect. 4.6. In this case Zerodur forms the cavity of an He-Ne laser for its operation it is important that the concentration of the He gas is kept constant over the lifetime of ten years of the gyroscope. On the other hand. He has the ability to diffuse rather easily through materials. Therefore, the He permeability of Zerodur and other competing materials has been investigated. Figure 4.8 demonstrates that the He permeability of Zerodur is more than two orders of magnitude lower than that of the other low-expansion materials ULE (7971) and fused silica (7940). 

Originally developed as a mirror substrate for large astronomical telescopes, Zerodur is today also used in X-ray telescopes and in a number of high-precision optical applications, such as laser gyroscopes, reflective optics for microlithography, or distance-defining parts in laser resonators. 

Fig. 4.70. Low helium permeability makes Zerodur the preferred material for laser gyroscopes in modern navigation technology...

B.C. Passenheim, C.E. Mallon Nuclear radiation vulnerability of ring laser gyroscope , SPIE Vol. 157 Laser Inertial Rotation Sensors, 205-211 (1978)... 

At the end of the project, Schott had created a new material for precision optics applications, had sold some telescope mirror blanks, but had also quite an amount of unsold material of different quality in stock. It was now up to the sales people to find other applications for Zerodur than telescope mirror substrates, thereby creating new markets for this new material. Relatively soon two new applications were found which will be described in more detail in Sect. 4.6 one was mirror substrates for reflective optics in microlithography, for which castings of approximately 500 mm in diameter were needed, and the other was housings for laser gyroscopes, for which continuous bars of cross sections of about 140 x 40 mm were the best delivery... 

An important application for Zerodur is laser gyroscopes as will be described in Sect. 4.6. In this case Zerodur forms the cavity of an He-Ne laser for its operation it is important that the concentration of the He gas... 

Applications of the Glass Ceramic Zerodur 227 4.6.2 Laser Gyroscopes... 

Applications include transparent cookware (Visions , thermal expansion = 7 x 10 V°C), optical materials (e.g., ring-laser gyroscopes), telescope mirror blanks (Zerodur ), infrared-transmitting electric range tops, wood-stove windows, fire door glazing... 

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