Passively Q-switched Microlaser Triggering
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Solution Overview
Problem
Passively Q-switched microchip lasers lack precision external trigger capability and have lower output compared to electro-optic or acousto-optic Q-switched lasers, particularly at wavelengths around 1.5-1.6 μm, which is crucial for applications like eyesafe distance measurement and optical communication, due to limitations in saturable absorbers and residual absorption.
Innovation Solution
A compact diode-pumped passively Q-switched microchip laser design utilizing an erbium-doped lasing medium and cobalt-doped saturable absorber, integrated with a short resonant cavity and an InGaAs photodiode for precise timing and high peak power pulse generation, optimized for wavelengths between 1.3-1.6 μm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a passive Q-switch is used, then the design is simpler and size is smaller, but precision external trigger capability is lost
Solution Approach 1:
A photodiode is introduced as an intermediary component to detect a portion of the laser pulses and generate electrical trigger signals. This mediator bridges the passive Q-switching mechanism with external triggering requirements, allowing precise timing control without compromising the passive design's simplicity.
2Device complexity
If a passive Q-switch is used, then the design is simpler and cost is lower, but output power is reduced due to residual absorption
Solution Approach 1:
The patent changes the material parameter of the saturable absorber from Cr:YAG to Co-doped spinel crystal. This parameter change reduces residual absorption at 1.5-1.6 μm wavelength, thereby increasing output power while maintaining the passive Q-switching mechanism's simplicity.
3Adaptability or versatility
If Cr:YAG is used as saturable absorber, then 1064 nm laser pulses can be generated, but wavelengths longer than 1.1 μm cannot be Q-switched
Solution Approach 1:
The patent changes the saturation wavelength parameter of the absorber material by selecting Co-doped spinel crystal, which has appropriate absorption characteristics for 1.5-1.6 μm wavelength. This enables reliable Q-switching in the eyesafe wavelength range while maintaining material stability.
4Power
If cobalt doped spinel crystal is used as saturable absorber, then ground state absorption cross section increases and excited state absorption cross section decreases, but residual absorption remains
Solution Approach 1:
The patent uses a composite structure combining Co-doped spinel crystal with an optical cavity design that includes a photodiode for detection. This composite approach maximizes the advantage of Co-doped spinel's high ground state absorption cross section while managing residual absorption through cavity optimization.
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 design achieves high peak power laser pulses with reduced timing jitter and increased sensitivity, enabling precise timing signals and improved performance in the 1.5-1.6 μm wavelength range, suitable for applications like eyesafe distance measurement and optical communication.
Implementation Method 1
a pump laser diode for emitting a pumping beam
Implementation Method 2
a saturable absorber disposed within said laser resonant cavity for generating laser pulses... the transmission varies with the incident optical intensity. As the incident optical intensity increases, the saturable absorber becomes more transparent
Implementation Method 3
a photodiode for detecting said reflected laser pulses by said filter
Data Source
AI summary
A passively Q-switched laser comprises a pump laser diode, a micro laser resonant cavity including a lasing medium and a saturable absorber, a filter and a photodiode. The lasing medium and saturable absorber are bonded together, and dielectric film is coated on the surfaces of the bonded body to form the laser resonant cavity. The filter reflects a portion of the Q-switched laser pulse beam. The photodiode can detect and convert the laser pulse to electric signal for triggering purpose.