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The authors discuss an increase in the precision of a laser interferometer based on the phase division of the fringe using a single-frequency laser for a distance measurement in the subnanometre range. The resolution of the interferometer is extended by using four paths of the laser beam across the measurement arm of the Michelson interferometer and by subsequent electronic division to the total resolution /2048. The technique fulfils the expectation that the influence of the fringe distortion caused by a phase difference of /2 between two quadrature signals and the difference of the intensities will be lower. A further improvement of the linearity can be achieved by using a mathematical method, which is based on the real-time measurement of parameters of the detected interferometer fringe and an optimal approximation of the quadrature signals obtained by using a conical section. The obtained parameters are transformed from the analytical form to the parametric form of the equation of the conical section and an inverse function is established. Reproducible measurements with an error of less than 0.5 nm are available now.

The design of a tunable extended-cavity semiconductor laser based on the modified Littman configuration is described. The mechanics of the extended cavity is designed with respect to applications as a stabilized laser source for an etalon of optical frequency, a laser for interferometry where stability, narrow linewidth, and mode hop free tuning range are required and for spectroscopic purposes with similar requirements. It follows the contradicting demands for a rigid construction and fine adjustability of the optical components. Optimisation of the optical feedback level and its influence of the laser behaviour are discussed and a method for the feedback level adjustment by rotation of the polarization plane is proposed. The laser parameters are presented for a version based on a laser diode operating at a wavelength of 633 nm.

In this contribution we propose a scheme for a generation of precise displacements through conversion of relative stability of components of a femtosecond laser into the length of a Fabry-Perot cavity. The spacing of mirrors of a Fabry-Perot interferometer represents a mechanical length standard referenced to stable optical frequency of a femtosecond mode-locked laser. With the help of a highly selective optical filter, it is possible to get only a few discrete spectral components. By tuning and locking the Fabry-Perot cavity to a selected single component it is possible to get a mechanical length standard with the uncertainty of the repetition frequency of the femtosecond laser. To verify the method, an auxiliary single-frequency laser is locked to the resonance mode of the cavity and simultaneously it is optically mixed with an independent optical frequency standard He-Ne-I2. The stability of the beat-frequency between these 2 lasers represents the stability of the Fabry-Perot cavity length. The stability recording evaluated through Allan variances for one hour of operation is presented. The pilot experimental setup is able to generate the length standard in the order of 0.01 nm for 20 min of integration time.