The importance of accurate length measurements in metrology
Accurate length measurements are fundamental to the field of metrology. These measurements are crucial in various areas, including manufacturing, engineering, and scientific research. Precise length calibration ensures that components fit together correctly, machines operate smoothly, and research results are reliable. For national metrology institutes like the Danish National Metrology Institute (DFM), maintaining high standards of accuracy in length measurements is essential. It helps set benchmarks that industries rely on for quality assurance and regulatory compliance.
Calibration of gauge blocks
Industrial companies typically use calibrated gauge blocks with precisely defined dimensions to calibrate their length measurement devices. However, these gauge blocks change over time and need to be regularly inspected and recalibrated. As the Danish National Metrology Institute, DFM provides accredited calibration of gauge blocks for length measurement equipment using various methods. The most accurate method is laser interferometry, where the length is determined from the interference patterns produced by two lasers at different wavelengths.
Interferometric length calibration
Interferometric setups for accurate gauge block calibration typically use two laser beams of different wavelengths to achieve a wide absolute measurement range. As the beams reflect and interfere, they generate interference patterns from which the exact length of the gauge block is determined with high accuracy.
Challenges faced with traditional interferometric set-ups
Traditionally, DFM and other metrology institutes have used commercial Zeeman-stabilized 633 nm Helium-Neon (HeNe) lasers and custom-made stabilized green HeNe lasers at 543 nm for length measurements. However, especially the latter laser presents certain challenges. A major issue is the availability of the 543 nm HeNe laser, which is no longer commercially produced. Additionally, HeNe lasers rely on gas tubes that require regular replacement and recalibration, a time-consuming process that can introduce inconsistencies in measurements.
Introducing DFM’s Stabiλaser 1542ε
DFM decided to replace the 543 nm HeNe laser with the 2nd harmonic 771 nm output from the Stabiλaser 1542ε. The Stabiλaser 1542ε is an acetylene-stabilized fiber laser that offers a narrow linewidth, excellent long-term stability, and high accuracy. By integrating the Stabiλaser 1542 into DFM’s interferometric length calibration system, we achieved a reliable, robust, and future-proof solution for length calibration.
Advantages of Using 771 nm Laser Line for Calibration
Besides replacement of the obsolete 543 nm laser, the 771 nm laser line from the Stabiλaser 1542ε offers numerous additional benefits for length calibration. First and foremost, the fiber laser technology ensures excellent long-term reliability. Unlike HeNe lasers, which rely on gas tubes needing frequent replacement, fiber lasers are more durable and require less maintenance. The Stabiλaser 1542ε operates according to the CIPM List of Recommended Frequency Standard Values, enabling its use as a primary length standard with direct traceability for the interferometric meter realization. When traceability relies on a Zeeman-stabilized HeNe laser, that HeNe laser must be regularly calibrated against another primary length standard, typically an iodine-stabilized HeNe laser. Hence, using a Stabiλaser 1542ε with the 771 nm option for interferometric gauge block calibration removes this extra calibration step and a single Stabiλaser 1542ε can effectively replace both a Zeeman-stabilized and an iodine-stabilized HeNe laser.
Additionally, the Stabiλaser 1542ε produces a cleaner interference pattern, leading to more robust and precise measurements. This improvement enhances the overall accuracy of the calibration process, ensuring that DFM’s measurements remain at the forefront of metrological standards.
Learn more about Stabiλaser 1542ε
The Stabiλaser 1542ε is available as a product from DFM. Read more about the features and specifications on the product page or contact DFM to discuss how Stabiλaser 1542ε can be integrated into your interferometric setup.