VHCRG Spatial Beam Deformation Correction
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Solution Overview
Problem
Volume holographic chirped reflection gratings (VHCRG) cause spatial distortion of optical pulses due to intrinsic DC index gradients, which affects the beam profile during pulse stretching and compression, detrimental for applications requiring distortion-free pulses.
Innovation Solution
The method involves either retracing and re-diffraction of the beam using a right angle mirror or prism to compensate for angular deflection or mechanically pre-deforming the VHCRG to counteract the index gradient-induced distortion, ensuring a clean beam profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If volume holographic chirped reflection gratings (VHCRG) are used for pulse stretching and compression, then the temporal length of optical pulses can be effectively controlled, but spatial distortion of the beam profile occurs due to intrinsic DC index gradients
Solution Approach 1:
The patent applies preliminary anti-action by introducing a compensating optical element (such as a cylindrical lens or prism) that pre-corrects the beam profile before it enters the VHCRG. This compensating element creates an opposite spatial distortion that cancels out the distortion caused by the DC index gradient in the grating, thereby maintaining beam quality while achieving pulse stretching and compression
Solution Approach 2:
The patent uses an intermediary optical component (cylindrical lens or prism) placed between the laser source and the VHCRG, or after the VHCRG, to mediate the beam propagation. This intermediary element introduces a controlled spatial transformation that compensates for the distortion caused by the grating's index gradient, allowing the beam to maintain its spatial profile throughout the pulse stretching and compression process
2Use of energy by moving object
If the DC index gradient in VHCRG is increased to improve diffraction efficiency, then more energy is concentrated in the first order, but spatial distortion of the beam is exacerbated
Solution Approach 1:
The patent introduces a cylindrical lens or prism as an intermediary element that decouples the relationship between diffraction efficiency and spatial distortion. This intermediary allows the VHCRG to operate with high DC index gradient for efficient energy concentration in the first order, while the intermediary element simultaneously corrects the spatial profile distortion, enabling both high efficiency and good beam quality
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
The proposed methods effectively correct spatial beam deformation, achieving a distortion-free beam profile after pulse stretching, amplification, and compression, as demonstrated by improved beam quality and coupling efficiency.
Implementation Method 1
Pulse stretchers based on volume holographic chirped reflection gratings (VHCRG) are used for increasing the temporal length of an optical pulse prior to amplification by an optical amplifier
Implementation Method 2
The DC index change is related to the illumination exposure and thus along the thickness of the sample, the DC index change varies continuously. The DC index gradient affects the propagation of a collimated beam
Data Source
AI summary
The invention disclosed here teaches methods and apparatus for altering the temporal and spatial shape of an optical pulse. The methods correct for the spatial beam deformation caused by the intrinsic DC index gradient in a volume holographic chirped reflective grating (VHCRG). The first set of methods involves a mechanical mean of pre-deforming the VHCRG so that the combination of the deflection caused by the DC index gradient is compensated by the mechanical deformation of the VHCRG. The second set of methods involves compensating the angular deflection caused by the DC index gradient by retracing the diffracted beam back onto itself and by re-diffracting from the same VHCRG. Apparatus for temporally stretching, amplifying and temporally compressing light pulses are disclosed that rely on the methods above.