A computer program serves as part of a feedback control system that locks the frequency of a laser to one of the spectral peaks of cesium atoms in an optical-absorption cell. The system analyzes a saturation absorption spectrum to find a target peak and commands a laser-frequency-control circuit to minimize an error signal representing the difference between the laser frequency and the target peak. The program implements an algorithm consisting of the following steps:
- Acquire a saturation absorption signal while scanning the laser through the frequency range of interest.
- Condition the signal by use of convolution filtering.
- Detect peaks.
- Match the peaks in the signal to a pattern of known spectral peaks by use of a pattern-recognition algorithm.
- Add missing peaks.
- Tune the laser to the desired peak and thereafter lock onto this peak.
Finding and locking onto the desired peak is a challenging problem, given that the saturation absorption signal includes noise and other spurious signal components; the problem is further complicated by nonlinearity and shifting of the voltage-to-frequency correspondence. The pattern-recognition algorithm, which is based on Hausdorff distance, is what enables the program to meet these challenges.
This program was written by Vahag Karayan, William Klipstein, Daphna Enzer, Philip Yates, Robert Thompson, and George Wells of Caltech for NASA’s Jet Propulsion Laboratory.
This software is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (818) 393-2827. Refer to NPO-41571.
This Brief includes a Technical Support Package (TSP).
Pattern-Recognition Algorithm for Locking Laser Frequency
(reference NPO-41571) is currently available for download from the TSP library.
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Overview
The document discusses a pattern-recognition algorithm developed for locking laser frequencies, primarily aimed at enhancing the precision and automation of laser applications. This technology is particularly relevant in fields requiring stable laser outputs, such as spectroscopy and atomic physics.
The algorithm operates by analyzing a saturated absorption signal to identify a target line, which is crucial for maintaining the laser's frequency. The process is fully automated, eliminating the need for user intervention. The system is designed to work with both Cesium and Rubidium cells, demonstrating its versatility in different experimental settings.
The implementation of the algorithm involves several key steps. Initially, the program requires a description of the target pattern, including the width and separation of lines in frequency terms. It also needs a rough understanding of the frequency-voltage correspondence and the voltage range to be scanned. The algorithm employs a combination of filtering, peak detection, and pattern matching to minimize the influence of noise and other unwanted features in the signal.
The high-level operations of the program mimic human operator behavior. It begins by scanning a wide range of frequencies to locate Doppler lines, then zooms in on saturated absorption features to identify the target line. The process involves adjusting the PZT (piezoelectric transducer) offset to center on the identified line, with fine adjustments made through the DTA (Digital-to-Analog) channel.
The document outlines the communication chain between the computer and the laser system, which includes a GPIB (General Purpose Interface Bus) connection for control and ATD (Analog-to-Digital) inputs for reading signals. The algorithm's robustness and flexibility are highlighted, showcasing its successful testing in various scenarios.
Overall, this technical support package emphasizes the significance of the developed algorithm in automating laser frequency locking, which can lead to advancements in various scientific and commercial applications. The document serves as a resource for understanding the underlying technology and its potential impact on future research and development in laser applications.
