Abstract: Wavelength measurements with Michelson interferometers have major disadvantages of high costs and low measurement rates. The paper shows two alternative method for wavelength measurement: one based on interference filters, the other based on double photodiodes. Interference filters are made of several optically transparent layers with different refraction indices. Within a certain wavelength range transmittance and reflectivity of the interference filter change constantly with the laser wavelength. Therefore, after calibration measurements, the wavelength can be obtained within milliseconds with a resolution of approximately plus or minus 0.01 nm by measuring the intensity of both the transmitted and the reflected beam. Double photodiodes are a combination of two single photodiodes with different spectral sensitivities in one case. Within a specified wavelength range both sensitivities are linear but have different gradients. Hence, by measuring the respective currents of each photodiode the wavelength can be obtained with a resolution of approximately plus or minus 0.1 nm also within milliseconds. Furthermore, the experimental set-up that is used for each method is illustrated, measurement results of both methods are presented, discussed and compared. !4
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