Relative Phase Measurement for Coherent Laser Beam Combining
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Solution Overview
Problem
Existing methods for coherent laser beam combination, such as Hansch-Couillaud detection, struggle with intensity dependence, leading to phase instability and additional phase disturbances due to intensity fluctuations, which limits the precision and stability of the combined sum laser beam.
Innovation Solution
The implementation of an interferometric measuring principle that generates multiple measuring beams with different phase offsets, allowing for intensity-independent phase measurement and stabilization through an adjustable delay device, enabling precise control of the relative phase between laser beams and compensating for intensity fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hansch-Couillaud detection is used for phase measurement, then phase control can be implemented, but intensity fluctuations cause additional phase disturbances and reduce stability
Solution Approach 1:
The measuring beam is divided into three separate measuring beams with different phase offsets (0, 120°, 240°) using a beam splitter and polarization optics. This segmentation allows the system to measure phase information through multiple independent channels, making the measurement process independent of intensity fluctuations and eliminating the phase disturbances caused by intensity variations in conventional single-channel detection methods
Solution Approach 2:
The system changes the measurement parameters by introducing three different phase offsets (0, 120°, 240°) to the measuring beams. This parameter change enables the system to extract phase information through the relative phases of multiple beams rather than relying on intensity-dependent single-beam detection, thereby achieving intensity-independent phase measurement and improved phase stability
2Reliability
If conventional phase measurement methods are used, then phase control is possible, but the resolution is limited and intensity-dependent fluctuations reduce control precision
Solution Approach 1:
The system implements a feedback control mechanism where the three photodetectors continuously monitor the relative phases of the measuring beams, and the measured phase information is fed back to adjust the optical path length difference between the laser beams. This feedback loop maintains phase stability with high resolution (0.001 rad rms) by continuously compensating for phase deviations while being immune to intensity fluctuations
Solution Approach 2:
The system uses three measuring beams with phase offsets of 0, 120°, and 240°, which exceeds the minimum two beams needed for phase measurement. This excessive action provides redundant measurement channels that improve measurement precision and enable better noise filtering, achieving phase resolution of 0.001 rad rms while maintaining intensity independence
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves improved phase stabilization with a resolution of 0.001 rad rms, reducing intensity-dependent fluctuations and enabling wide bandwidth control, even at low laser repetition rates, resulting in a more stable and coherent sum laser beam.
Implementation Method 1
a beam splitter for generating at least three measuring beams from the coherent laser beams of the measuring portion
Implementation Method 2
the at least three measuring beam paths of the at least three measuring beams are formed by projection onto adapted polarization directions
Implementation Method 3
at least three photodetectors for outputting photodetector signals. The photodetectors are assigned to one of the measuring beam paths or one of the measuring beam regions, respectively, and the photodetector signals correspond to the measuring beams or measuring beam regions at the different phase offsets
Implementation Method 4
the coherent laser beams of the measuring portion propagate spatially superimposed at an angle and form at least three measuring beam regions
Implementation Method 5
a delay device for being inserted into the beam path of at least one of the two laser beams that are to be superimposed collinearly. The delay device has an optical path length that is adjustable in dependence on the control signal
Data Source
AI summary
A phase control system for controlling the relative phase (φ) of two laser beams of a laser system, which are to be coherently combined, is disclosed that enables providing a phase-controlled sum laser beam. An optical system of the phase control system includes a beam input for receiving a measuring portion of two collinear coherent laser beams, which are superimposed to form a sum laser beam, and provides measuring beams or measuring beam regions, which are used with associated photodetectors for outputting photodetector signals. For determining the relative phase from the photodetector signals, the phase control system has an evaluation device and a delay device for being inserted into the beam path of at least one of the two laser beams. The optical system is configured such that the measuring beams or measuring beam regions are related to different phase offsets.