Passively Q-switched Microlaser Peak Power Control
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Solution Overview
Problem
Passively Q-switched microchip lasers lack a simple and practical means to control output pulse parameters such as pulse energy, pulse duration, and peak power density, which is essential for various applications like MALDI and time-of-flight ranging, due to their design limitations and sensitivity to misalignment and vibrations.
Innovation Solution
A simplified design that varies the optical path lengths of the gain and saturable absorber media within the laser cavity by transverse translation of the microchip, using wedged-shaped blocks optically contacted to form a single parallel-faced block, allowing control of output pulse energy, pulse duration, and peak power density in a cost-effective and stable manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If pump power is increased to increase pulse energy, then pulse energy increases, but pulse duration and peak power remain uncontrollable
Solution Approach 1:
The patent introduces a movable focusing lens that can be dynamically adjusted along the optical axis to change the pump beam focus position within the gain medium. This dynamic adjustment allows independent control of pulse energy, pulse duration, and peak power by varying the focus position, transforming the static laser cavity into a controllable system with multiple degrees of freedom.
Solution Approach 2:
The patent changes the physical parameter of pump beam focus position to control laser output characteristics. By moving the focusing lens to different positions, the pump beam waist location and size within the gain medium changes, which directly affects the pumped volume, gain distribution, and consequently the pulse energy, duration, and peak power independently.
2Quantity of substance
If focusing optics are translated to adjust pump beam focus, then pulse energy can be controlled, but positioning tolerances are very tight requiring high precision mechanical mounting
Solution Approach 1:
The patent replaces the complex high-precision mechanical mounting system with a simpler focusing lens translation mechanism. By adjusting the focus position along the optical axis rather than requiring precise lateral positioning, the system achieves pulse energy control with relaxed mechanical tolerance requirements.
3Power
If output-coupling mirror with variable reflection coefficient is used, then cavity losses can be adjusted to control peak power, but lateral translation is technically difficult and expensive
Solution Approach 1:
The patent extracts the control function from the output-coupling mirror and implements it through the pump beam focusing mechanism. Instead of modifying the mirror properties or requiring lateral translation, the system uses the existing focusing lens to control peak power by adjusting the pump beam waist position and size within the gain medium.
4Power
If microchip lateral translation is used to adjust output coupling, then peak power can be controlled, but this requires independent coating of every microchip
Solution Approach 1:
The patent replaces the mechanical lateral translation method with optical focusing control. By using a movable focusing lens to adjust the pump beam parameters, the system achieves peak power control without requiring any modification to the microchip structure or coating, preserving mass production capabilities.
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
Enables continuous and stable control of output performance parameters with minimal complexity and cost, reducing sensitivity to misalignment and vibrations, while maintaining the advantages of monolithic laser cavities, such as compact size and high peak power.
Implementation Method 1
a block of gain medium... A pump beam is directed onto the microchip, which causes a lasing beam to oscillate
Implementation Method 2
a block of saturable absorber... The saturable absorber and the gain medium are optically contacted together to form a single parallel-faced block
Data Source
Figure 1
Figure 2
Figure 3a
AI summary
Geometrical design of laser microchips is disclosed that allows variation of the optical path length in the different media by simple displacement of the microchip, the movement having a non-zero projection orthogonal to the pump beam. The concept can be implemented to vary optical loss in the lasing cavity, the absorbed pump power, or the optical length of the cavity. Passively Q-switched microchip laser output performance can thus be controlled by simple transverse displacement of the microchip relative to the pump beam. The above microlaser can be combined with voltage -controlled variable-focus output optics in order to contro 1 the peak power density of the laser pulses.