On the performance of wavelength meters: Part 2\u2014frequency-comb based characterization for more accurate absolute wavelength determinations

Kristian König,Bernhard Maaß,Tim Ratajczyk,Wilfried Nörtershäuser,Felix Sommer,Konstantin Mohr,Phillip Imgram,Jörg Krämer

doi:10.1007/s00340-020-07433-4

Abstract

Wavelength meters are widely used for frequency determinations and stabilization purposes since they cover a large wavelength range, provide a high read-out rate and have specified accuracies of up to 10^{-8}. More accurate optical frequency measurements can be achieved with frequency combs but only at the price of considerably higher costs and complexity. In the context of precise and accurate frequency determinations for high-resolution laser spectroscopy, the performance of five different wavelength meters was quantified with respect to a frequency comb. The relative precision as well as the absolute accuracy has been investigated in detail, allowing us to give a sophisticated uncertainty margin for the individual instruments. We encountered a prominent substructure on the deviation between both device types with an amplitude of a few MHz that is repeating on the GHz scale. This finally limits the precision of laser scans which are monitored and controlled with wavelength meters. While quantifying its uncertainty margins, we found a high temporal stability in the characteristics of the wavelength meters which enables the preparation of wavelength-dependent adjustment curves for wide- and short-ranged scans. With this method, the absolute accuracy of wavelength meters can be raised up to the MHz level independently from the wavelength of the reference laser used for calibrating the device. Since this technique can be universally applied, it can lead to benefits in all fields of wavelength meter applications.

Highlights

Accurate determinations of laser frequencies and frequency differences or the corresponding stabilization at a fixed frequency are crucial for many laser spectroscopy experiments and can rely on several approaches: natural transition lines in atoms, ions or molecules offer the opportunity to lock lasers at well-known but fixed frequencies [1,2,3,4]
Five different characteristics of the wavelength meters were investigated in this study: to quantify the scanning behavior, coarse scans spanning several GHz were performed at several points in the accessible optical spectrum
We demonstrated that a wavelength-dependent adjustment curve for the absolute frequency determination can be extracted from such measurements leading to a significant gain in the accuracy for experiments applying this wavelength meter

Summary

Introduction

Accurate determinations of laser frequencies and frequency differences or the corresponding stabilization at a fixed frequency are crucial for many laser spectroscopy experiments and can rely on several approaches: natural transition lines in atoms, ions or molecules offer the opportunity to lock lasers at well-known but fixed frequencies [1,2,3,4]. We use the term “absolute” frequency to refer to a measurement where we are interested in the actual value of the laser frequency in contrast to measurements of relative stability to a fixed value. It is measured with a GPS-referenced frequency comb relative to the SI second. 86 Page 2 of 8 expensive, more complex to handle and not well suited to control fast laser scans Even though they are used in numerous applications, to our knowledge only the long-term stability of wavelength meters has been investigated in detail so far [11, 12]. The absolute accuracy has been tested as well in comparison to a frequency comb and enabled us to generate individual calibration curves for more accurate wavelength measurements

Methods

Results

Conclusion