Acousto-Optic Modulator Pulse Selection for Laser Systems
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Solution Overview
Problem
Existing methods for reducing the pulse repetition frequency (PRF) in pulsed laser systems, particularly using acousto-optical modulators, suffer from amplitude fluctuations and intensity noise, and are not applicable to CE-phase-stable laser pulse trains, which are sensitive to these fluctuations and frequency shifts.
Innovation Solution
Synchronizing the high-frequency carrier signal with the laser pulse train and switching signal, ensuring the carrier signal is phase-stable and its frequency is a rational multiple of the PRF, to maintain consistent diffraction efficiency and CE phase stability, thereby reducing relative peak intensity noise and allowing PRF reduction in CE-phase-stable systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If acousto-optical modulator is used to reduce PRF by selecting individual laser pulses, then pulse peak power and pulse energy are improved, but amplitude fluctuations and intensity noise increase due to varying diffraction efficiency
Solution Approach 1:
The patent applies dynamics by making the carrier signal frequency adjustable and synchronizing it with the laser pulse repetition frequency. The system dynamically adapts the carrier frequency to be an integer multiple of the PRF, ensuring that the diffraction grating is always formed at the optimal position relative to the laser beam, thereby eliminating amplitude fluctuations while maintaining high pulse peak power.
Solution Approach 2:
The patent changes the parameter of carrier signal frequency from a fixed value to a dynamically adjustable parameter that is synchronized with the laser pulse repetition frequency. By setting the carrier frequency to an integer multiple of the PRF, the system optimizes the diffraction efficiency and eliminates amplitude fluctuations, thus improving both pulse peak power and amplitude stability.
2Power
If acousto-optical modulator is used to reduce PRF, then pulse energy is improved, but the method is not applicable to CE phase-stable laser pulse trains due to added frequency components
Solution Approach 1:
The patent applies dynamics by making the carrier signal frequency adjustable and synchronizing it with the laser pulse repetition frequency. The system dynamically adapts the carrier frequency to be an integer multiple of the PRF, ensuring that the diffraction grating is always formed at the optimal position relative to the laser beam, thereby eliminating amplitude fluctuations while maintaining high pulse peak power.
Solution Approach 2:
The patent changes the parameter of carrier signal frequency from a fixed value to a dynamically adjustable parameter that is synchronized with the laser pulse repetition frequency. By setting the carrier frequency to an integer multiple of the PRF, the system optimizes the diffraction efficiency and eliminates amplitude fluctuations, thus improving both pulse peak power and amplitude stability.
3Ease of operation
If electro-optical switches (Pockels cells) are used to reduce PRF, then pulse selection is achieved, but very high voltages are required making switching difficult and expensive
Solution Approach 1:
The patent replaces the electro-optical switching mechanism (Pockels cells requiring high voltages) with an acousto-optical modulation approach. Instead of using electric fields to change refractive index, the system uses acoustic waves to create a diffraction grating that selectively directs laser pulses. This substitution eliminates the need for high-voltage power electronics and complex switching circuits, simplifying the overall system while maintaining pulse selection capability.
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 stabilizes the diffraction grating position within the acousto-optical modulator, reduces amplitude fluctuations, and maintains CE phase stability, enabling efficient pulse selection with reduced intensity noise and increased pulse peak power, applicable to both conventional and CE-phase-stable laser systems.
Implementation Method 1
The switching principle used in AOMs is that the laser radiation is diffracted at a refractive index modification (Bragg grating), which is generated in an optical crystal by high-frequency sound waves
Implementation Method 2
the laser radiation is diffracted at a refractive index modification (Bragg grating), which is generated in an optical crystal by high-frequency sound waves via a piezoelectric crystal
Implementation Method 3
high-frequency sound waves via a piezoelectric crystal controlled with a correspondingly high-frequency electrical signal
Implementation Method 4
Pockels cells use the Pockels effect to change the refractive index of a birefringent nonlinear medium by generating an electric field
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for generating a laser pulse train, having the following method steps: - generating the laser pulse train (4a) at a pulse repetition frequency; coupling the laser pulse train (4a) into an acousto-optic modulator; and selecting individual laser pulses of the laser pulse train (4a) by actuating the acousto-optic modulator using high-frequency pulses (4h), wherein the high-frequency pulses (4h) are generated by modulating a high-frequency carrier signal (4f) with a periodic switching signal (4e). The invention additionally relates to a system for generating a laser pulse train, comprising a pulse laser (1) which generates the laser pulse train at a pulse repetition frequency, comprising an acousto-optic modulator (2) in which the laser pulses propagate, and comprising a controller (7) which actuates the acousto-optic modulator (2) using high-frequency pulses in order to select individual laser pulses. The aim of the invention is to provide an improved method for selecting individual laser pulses from a laser pulse train. The intensity noise known from the prior art is to be reduced. This is achieved in that for the frequency f HF of the carrier signal (4f) of the high high-frequency pulses (4h), the following applies: f HF =n/p ⋅ f PRF , where n is any natural number and p specifies the whole-number ratio between the pulse repetition frequency and the frequency of the switching signal (4e), and the carrier signal (4f) is coupled to the laser pulse train (4a) in a phase-stable manner.