Acousto-Optic Delay Scanning Using Bragg Diffraction
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Solution Overview
Problem
Current scanning methods for ultrashort optical pulses, such as mechanical delay lines and asynchronous optical sampling, are limited by low scanning rates, precision, and stability, making them unsuitable for analyzing processes on femtosecond and attosecond timescales.
Innovation Solution
The method employs acousto-optic Bragg diffraction in a bulk crystal to generate a time-dependent delay for ultrashort optical pulses, allowing for high-speed and precise scanning with a repetition rate of over 1 kHz and precision of 1 fs or better, using a multifrequency acoustic signal to control the optical pulse delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mechanical delay lines are used for scanning ultrashort optical pulses, then the delay can be controlled by adjusting optical path lengths, but the scanning rate is limited to a few tens of Hertz due to mechanical inertia
Solution Approach 1:
The patent replaces the mechanical delay line with an acousto-optic device that uses acoustic waves to create a time-dependent optical path difference. The acoustic wave modulates the refractive index of the crystal, creating a moving grating that delays the optical pulse by a controllable amount without any mechanical moving parts, thereby achieving high scanning rates while maintaining stability
Solution Approach 2:
The patent changes the controlling parameter from mechanical displacement to acoustic frequency. By varying the frequency and amplitude of the acoustic wave applied to the acousto-optic crystal, the optical delay can be precisely controlled over a wide range at high repetition rates, eliminating the mechanical inertia limitation
2Speed
If rotatable mirrors or quickly moving loudspeaker diaphragms are used to increase scanning rate to 100 Hz up to a few kHz, then the scanning speed improves, but the time jitter between scans exceeds one femtosecond reducing precision
Solution Approach 1:
The patent eliminates all mechanical moving parts by using an acousto-optic device where the acoustic wave creates a virtual moving grating in the crystal. This acoustic field can be modulated with extremely high precision and stability, achieving time jitter well below one femtosecond while maintaining high scanning rates, thus resolving the contradiction between speed and precision
3Measurement precision
If acousto-optic deflector is used to eliminate one source of timing jitter, then timing stability improves, but the delay scanning occurs in discontinuous steps and mechanical stability issues remain
Solution Approach 1:
The patent uses a continuous acoustic wave that can be amplitude-modulated to create smooth, continuous delay scanning. The acoustic field continuously fills the interaction region, allowing the optical delay to vary continuously rather than in discrete steps, thereby achieving both high timing stability and continuous scanning 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 achieves rapid and precise scanning with a high repetition rate and sub-femtosecond precision, significantly improving the ability to analyze ultrafast dynamics without the limitations of mechanical instability and electronic jitter, enabling detailed study of phenomena on short timescales.
Implementation Method 1
The method is based on acousto-optic diffraction under Bragg conditions, denominated as Bragg diffraction
Implementation Method 2
The diffracting acoustic wave is generated by an acousto-optic device in which an ultrashort acoustic pulse is launched at the arrival of each optical pulse
Data Source
Figure 1
Figure 2
Figure 3A~4B
AI summary
A method and a system for scanning a time delay between pairs of a first ultrafast optical pulse of duration shorter than 10 ps and of a second ultrafast optical pulse of duration shorter than 10 ps, wherein said second ultrafast pulse is submitted to an acousto-optic Bragg diffraction by an acoustic pulse in the bulk of an acousto-optic material and the delay scanning is produced by time variation of said acoustic pulse in said material.