Related Experiment Video
Updated: Jul 7, 2026

Label-free Single Molecule Detection Using Microtoroid Optical Resonators
Published on: December 29, 2015
Frequency-locked light scattering: real-time Doppler velocimetry with closed-loop feedback control
Abstract:
Real-time measurement capability of a frequency-modulated filtered light-scattering- (FM FLS) Doppler velocimeter has been demonstrated. Doppler-shifted light from a frequency-modulated Ti:sapphire laser scattered from a supersonic flow is imaged through a potassium vapor cell and is detected by FM spectroscopy. The FM signal is used in closed-loop feedback control of the laser frequency to lock the Doppler-shifted scattered light to the resonance frequency of the filter. The difference between the filter resonance frequency and the laser frequency when the scattered light is frequency locked to the filter resonance is the flow-induced Doppler shift. Changes in flow velocity are tracked by changes in laser frequency, which is subsequently measured to obtain the Doppler shift. The frequency-locking capability of the technique was achieved with use of a simple analog controller. The random Doppler shift measurement errors (2varsigma) were approximately 20 MHz, which correspond to velocity measurement errors for the real-time measurement of less than 3% in a 10-Hz bandwidth.
More Related Videos
09:10The Frequency Domain Thermoreflectance Technique for Thermal Property Measurements
Published on: December 5, 2025
09:01Gain-compensation Methodology for a Sinusoidal Scan of a Galvanometer Mirror in Proportional-Integral-Differential Control Using Pre-emphasis Techniques
Published on: April 4, 2017
Related Concept Videos
Open and closed-loop control systems
An open-loop control system operates without feedback from the output. It consists of two primary elements: the controller and the controlled process. The controller receives an input signal and...
Feedback control systems
Linear feedback systems are theoretical models that simplify analysis and design. These systems operate under the principle that their output is directly proportional to their input within certain ranges. For instance, an amplifier in a control system behaves linearly as long as the input signal remains within a specific range. However, most physical systems exhibit inherent nonlinearity...
Doppler Effect - II
Time and frequency -Domain Interpretation of Phase-lag Control
Phase-lag controllers do not place a pole at zero, but instead influence the steady-state error by amplifying any finite,...
Doppler Effect - I
PID Controller