Astigmatic Multipass Cell for Ultrashort Pulse Bandwidth Broadening

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Solution Overview

Problem

Existing optical assemblies for material processing using ultrashort pulse lasers face challenges in bandwidth enlargement through self-phase modulation (SPM) due to self-focusing caused by the Kerr effect, leading to reduced beam quality and potential damage to optical units from high power density.

Innovation Solution

An optical arrangement utilizing a multipass cell with a nonlinear medium, where the laser beam is shaped into an astigmatic beam and passes through the nonlinear medium multiple times, preventing self-focusing and maintaining beam quality by using a Herriot multipass cell or other configurations with carefully arranged mirrors and stop arrays for dispersion compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If self-phase modulation is used to enlarge bandwidth, then spectral bandwidth is enlarged, but beam quality is reduced due to self-focusing caused by the Kerr effect

Engineering Contradiction:

Improvespectral bandwidthVSAvoidbeam quality

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The optical path is segmented into multiple passes through the nonlinear medium, allowing the beam to interact with the medium multiple times at lower intensity levels rather than concentrating all energy in a single pass, thereby avoiding self-focusing while achieving cumulative bandwidth enlargement

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The beam path is nested within a multipass cavity structure where the beam traverses the nonlinear medium multiple times through reflective optics, effectively embedding the bandwidth enlargement process within a controlled optical loop that prevents catastrophic self-focusing

Inventive Principle:

Principle #7Nested doll (Nesting)

2Manufacturing precision

If stigmatic beams are used for material processing, then processing precision is improved, but optical units are damaged due to excessively high power density at focuses

Engineering Contradiction:

Improveprocessing precisionVSAvoidpower density

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The beam is transformed from a symmetric stigmatic profile to an asymmetric astigmatic profile with different focal characteristics in orthogonal planes, allowing the beam to be focused in one plane while remaining defocused in the perpendicular plane, thereby reducing peak power density at optical components

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The beam focusing problem is extended from one dimension to two dimensions by creating astigmatic beams that focus in one transverse dimension while being defocused in the orthogonal dimension, effectively distributing the power density across a larger volume and protecting optical units from damage

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Use of energy by moving object

If amplifier arrangements are used to generate high pulse energy, then pulse energy is increased, but pulse duration is lengthened due to gain narrowing

Engineering Contradiction:

Improvepulse energyVSAvoidpulse duration

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of moving object

Solution Approach 1:

The beam is pre-shaped into an astigmatic profile before entering the amplifier and nonlinear medium, establishing a beam configuration that maintains low power density throughout the amplification and bandwidth enlargement process, preventing self-focusing even at high pulse energies

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The beam parameters are changed from stigmatic to astigmatic, fundamentally altering the spatial distribution of energy and allowing the system to handle high pulse energies without the catastrophic self-focusing that would occur with conventional stigmatic beams

Inventive Principle:

Principle #35Parameter changes

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 allows for a defined enlargement of spectral bandwidth without reducing beam quality and avoids damage to optical units, enabling precise and efficient material processing with ultrashort pulses.

Implementation Method 1

bandwidth enlargement by self-phase modulation (SPM)

Methodology Applied

Scientific EffectSelf-phase modulation:

Implementation Method 2

self-focusing, caused by the Kerr effect

Methodology Applied

Scientific EffectKerr effect: Kerr Effect

Data Source

PatentUS12259632B2Optical assembly for enlarging spectral bandwidths and reducing ultrashort pulses

Publication Date: 2025.03.25 DU KEMING

AI summary

An optical arrangement for enlarging spectral bandwidths by nonlinear self-phase modulation for shortening ultrashort pulses using a multipass cell and a nonlinear medium. The nonlinear medium is arranged within the multipass cell, and a laser beam having ultrashort pulses passes through the nonlinear medium multiple times. The laser beam is coupled into the multipass cell by way of a shaping optical unit. The laser beam is shaped into an astigmatic beam and coupled into the multipass cell by way of the shaping optical unit.