Tunable Laser Diode Wavelength Stabilization via Absorption Spectroscopy

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Solution Overview

Problem

Conventional laser trackers using HeNe lasers face challenges due to their large size, high power consumption, sensitivity to magnetic fields, and limited lifespan, while conventional Fabry-Pérot laser diodes are not suitable for interferometry due to short coherence length and multi-mode emission, making it difficult to stabilize and accurately determine the emission wavelength for precise distance measurements.

Innovation Solution

A compact laser tracker design utilizing a tunable laser diode with a stored spectral atlas for absorption lines, allowing for mode-hop-free wavelength tuning and stabilization, enabling unique identification and stabilization of the emission wavelength through a control and evaluation unit, ensuring reliable and precise distance measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If HeNe laser sources are used for interferometric measurements, then wavelength stability and coherence length are improved, but device size and power consumption increase

Engineering Contradiction:

Improvewavelength stabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by stationary object

Solution Approach 1:

The patent transitions from gas laser to laser diode light sources, fundamentally changing the operating parameters (electrical current, temperature control) to achieve comparable wavelength stability with reduced power consumption and device size

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses laser diodes as a alternative light source that copies the essential functions of HeNe lasers (coherence, monomode emission) while eliminating their disadvantages (size, power consumption, magnetic sensitivity)

Inventive Principle:

Principle #26Copying

2Use of energy by stationary object

If laser diodes are used as interferometer light sources, then device size and power consumption are reduced, but wavelength stability and coherence length deteriorate

Engineering Contradiction:

Improvepower consumptionVSAvoidwavelength stability

Core Design Contradiction:

Use of energy by stationary objectVSReliability

Solution Approach 1:

The patent implements feedback control by detecting absorption lines of a reference gas and using this information to actively stabilize the laser diode emission wavelength, ensuring long-term wavelength stability despite drift

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces mechanical wavelength stabilization methods with optical detection of absorption lines, using the reference gas absorption spectrum as a stable reference for wavelength locking

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Volume of moving object

If conventional Fabry-Pérot laser diodes are used, then device size is reduced, but coherence length and single-mode emission are compromised

Engineering Contradiction:

Improvedevice sizeVSAvoidsingle-mode emission

Core Design Contradiction:

Volume of moving objectVSStability of the object's composition

Solution Approach 1:

The patent carefully controls the drive current and temperature parameters of the laser diode to ensure operation in the single-mode regime, maintaining coherence length sufficient for interferometric measurements while keeping the device compact

Inventive Principle:

Principle #35Parameter changes

4Measurement precision

If absorption lines are used for wavelength stabilization, then wavelength accuracy is improved, but identification difficulty increases when lines are closely spaced

Engineering Contradiction:

Improvewavelength accuracyVSAvoidline identification

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent uses a reference gas with well-known absorption line spectrum as an intermediary medium. The absorption lines serve as a stable reference framework that simplifies wavelength identification and stabilization, even when lines are closely spaced

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution provides a compact, reliable, and precise method for stabilizing the emission wavelength of laser diodes in laser trackers, enabling accurate distance measurements with improved reliability and reduced susceptibility to wavelength variations, even with close absorption lines.

Implementation Method 1

an absorption medium defining a multiplicity of known absorption lines within the wavelength range

Methodology Applied

Scientific EffectAbsorption spectroscopy: Absorption Spectroscopy

Data Source

PatentUS11067690B2Measuring apparatus comprising an interferometer and an absorption medium defining a dense line spectrum

Publication Date: 2021.07.20 LEICA GEOSYSTEMS AG

AI summary

A measuring apparatus comprising a tunable laser diode for generating a mono mode measurement radiation, said laser diode being designed as a laser beam source in such a way that an emission wavelength of the measurement radiation is variable within a wavelength range by means of the variation of a tuning parameter, comprising an absorption medium defining absorption lines within the wavelength range, comprising a memory having a line atlas for the absorption medium, comprising a detector for determining an absorptivity and comprising a control and evaluation unit for regulating the emission wavelength by means of the at least one tuning parameter in a manner dependent on the absorptivity determined in such a way that the emission wavelength remains stable.