Microwave Gas Slab Laser Photonic Band-Gap Waveguide
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Solution Overview
Problem
The output power of microwave excited gas slab lasers is limited by the allowed RF power load per unit area, which is restricted by the electrode spacing, leading to thermal deleterious effects and waveguide losses, making it difficult to achieve higher power densities without reducing laser efficiency.
Innovation Solution
A microwave excited gas slab laser using a one-dimensional photonic band-gap waveguide formed by alternating dielectric layers, such as aluminum oxide and germanium, reduces electrode spacing while minimizing waveguide losses, allowing for higher RF power investment and stable CW operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the electrode spacing is reduced to allow higher RF power load per unit area, then the power density increases, but the waveguide losses increase dramatically due to the 1/d^3 relationship
Solution Approach 1:
The patent changes the operating frequency parameter from traditional RF (100-200 MHz) to microwave frequencies (2.45 GHz), which fundamentally alters the waveguide loss characteristics and enables reduced electrode spacing without prohibitive losses
Solution Approach 2:
The patent introduces a layered dielectric structure with alternating high and low refractive index materials, creating a photonic bandgap structure that confines light in the third dimension (transverse direction) while allowing propagation in the longitudinal direction, thus reducing waveguide losses
2Power
If the electrode spacing is reduced to increase power density, then higher RF power load is achieved, but thermal deleterious effects worsen due to insufficient cooling
Solution Approach 1:
The patent changes the excitation frequency from RF to microwave range, which allows for reduced electrode spacing and improved heat dissipation while maintaining or increasing power density
Solution Approach 2:
The patent implements pre-cooling of the gas mixture and electrode structures before discharge initiation, and maintains continuous cooling during operation to prevent thermal accumulation at high power densities
3Power
If the electrode spacing is reduced to allow higher RF power load, then power scaling is improved, but the depletion layers occupy a larger fraction of the discharge volume, reducing the gain volume
Solution Approach 1:
The patent increases the excitation frequency from 100-200 MHz to 2.45 GHz, which reduces the depletion layer width and allows for smaller electrode spacing while maintaining adequate gain volume
Solution Approach 2:
The patent creates a narrow discharge channel in the transverse dimension while maintaining adequate length in the longitudinal dimension, effectively optimizing the volume utilization for gain production
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 configuration enables an order of magnitude higher RF power load per unit area without deteriorating laser efficiency, achieving stable and efficient operation with reduced waveguide losses and increased power scaling, along with improved stability and reduced size and cost of the laser source.
Implementation Method 1
Microwave excited CO2 lasers are for instance reviewed in the Ph.D. thesis of Avi Shahadi, 'Microwave excited CO2 lasers', Tel-Aviv University, March 2001
Implementation Method 2
Diffusion-cooled, gas-discharge slab lasers are characterized by output power of several watts per unit area of discharge
Implementation Method 3
a special optical waveguide at 10.6 μm wavelength, based on a one-dimensional (1D) photonics band-gap waveguide formed by alternating dielectric layers
Implementation Method 4
Suitable dielectric materials are transparent to the MW wavelength and are not affected by the laser plasma (plasma heat damages, possible degradation due to plasma emission of deleterious particles and photons)
Implementation Method 5
allowing for maximum exploitation of the discharge gain volume for a single mode beam amplification
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~4
AI summary
A microwave excited gas slab laser comprising a waveguide wherein the electrodes are covered with multi-layered stripes either forming a photonic band-gap or having a refractive index lower than 1.