Laser Pulse Length Control via Cycle Adjustment

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Solution Overview

Problem

Ultrashort laser pulses experience peak intensity reduction due to stretching when passing through optics, particularly affecting shorter pulses more significantly, which complicates material processing in medical and scientific applications.

Innovation Solution

A system comprising a laser source, optical elements, a monitoring device, and a control computer that measures and compensates for pulse length changes by adjusting laser parameters, such as applying a negative chirp to counteract positive dispersion, ensuring desired pulse length and energy at the target.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If laser pulses pass through optics to reach the target, then the laser system can perform material processing, but the optics stretch the laser pulses which reduces peak intensity

Engineering Contradiction:

Improvepeak intensityVSAvoidpulse length

Core Design Contradiction:

Illumination intensityVSDuration of action of moving object

Solution Approach 1:

The system applies preliminary action by adjusting the laser source parameters (cycle number, pulse duration) before the pulses pass through the optics. The control computer calculates compensation parameters based on measured pulse length and adjusts the laser source to pre-compensate for the expected stretching, ensuring the pulses arrive at the target with the desired peak intensity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements feedback by using a monitoring device to measure the actual pulse length after passing through the optics, then feeding this information back to the control computer. The control computer uses this feedback to adjust the laser source parameters for subsequent pulses, creating a closed-loop control system that maintains optimal peak intensity.

Inventive Principle:

Principle #23Feedback

2Illumination intensity

If shorter laser pulses are used to achieve higher peak intensity, then the pulse duration is reduced, but the pulses experience greater stretching when passing through optics

Engineering Contradiction:

Improvepeak intensityVSAvoidpulse length control

Core Design Contradiction:

Illumination intensityVSManufacturing precision

Solution Approach 1:

The system applies dynamics by making the laser source parameters adjustable and variable. The control computer dynamically changes the cycle number and pulse duration settings based on the measured pulse length and desired compensation, allowing the system to adapt to different operating conditions and maintain precise control over the final pulse characteristics.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system implements parameter changes by modifying the laser source parameters (cycle number, pulse duration, repetition rate) to compensate for the stretching effect. The control computer calculates the required parameter adjustments based on the measured pulse length and applies these changes to restore the desired pulse characteristics at the target.

Inventive Principle:

Principle #35Parameter changes

3Illumination intensity

If the laser source parameters are adjusted to compensate for pulse stretching, then the peak intensity is maintained, but the system complexity increases

Engineering Contradiction:

Improvepeak intensityVSAvoidsystem complexity

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The system implements self-service by using the monitoring device to measure the actual pulse length and automatically having the control computer calculate and apply the necessary compensation parameters. The system monitors its own performance and self-adjusts without requiring external intervention, maintaining peak intensity through automated feedback control.

Inventive Principle:

Principle #25Self-service

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

Maintains or minimizes pulse length, thereby preserving peak intensity and reducing unwanted effects like scattered radiation and gas bubbles, enhancing the precision and effectiveness of laser-induced optical breakdown in material processing.

Implementation Method 1

the monitoring device measures the pulse length of the laser pulses to detect the change in the pulse length

Methodology Applied

Scientific EffectTime measurement:

Implementation Method 2

determines one or more laser parameters that compensate for the change in the pulse length, such as applying a negative chirp to counteract positive dispersion

Methodology Applied

Scientific EffectNegative chirp: Phase Modulation

Implementation Method 3

The optics, however, may stretch the laser pulses with respect to time

Methodology Applied

Scientific EffectDispersion: Dispersion (of waves)

Data Source

PatentUS9755393B2Controlling a laser source to compensate for change in pulse length by adjusting cycle number of an amplifier

Publication Date: 2017.09.05 ALCON INC

AI summary

In certain embodiments, a system (10) comprises a laser source (20), one or more optical elements (24), a monitoring device (28), and a control computer (30). The laser source (20) emits one or more laser pulses. The optical elements (24) change a pulse length of the laser pulses, and the monitoring device (28) measures the pulse length of the laser pulses to detect the change in the pulse length. The control computer (30) receives the measured pulse length from the monitoring device (28), determines one or more laser parameters that compensate for the change in the pulse length, and controls the laser source (20) according to the laser parameters.