Intra-cavity Frequency-Converted OPS Laser Design
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Solution Overview
Problem
Intra-cavity frequency-converted optically-pumped semiconductor (OPS) lasers face efficiency issues in generating third-harmonic radiation at wavelengths less than 355 nm due to the steep fall-off in type-II sum-frequency mixing efficiency, and the need for additional birefringent optical elements increases costs in bio-instrumentation applications.
Innovation Solution
A laser-resonator design incorporating a birefringent filter between two optically nonlinear crystals to polarize and rotate the fundamental and second-harmonic radiation, enabling type-I sum-frequency mixing without additional birefringent elements, thereby generating third-harmonic radiation efficiently at lower wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If type-II sum-frequency mixing is used to generate third-harmonic radiation, then the arrangement provides automatic polarization orientation alignment, but the efficiency falls off steeply at wavelengths less than 355 nm
Solution Approach 1:
The patent changes the mixing type from type-II to type-I sum-frequency mixing, which fundamentally alters the polarization requirements and efficiency characteristics. Type-I mixing maintains high efficiency down to 280 nm by using identical polarization orientations for both input beams, unlike type-II which has steep efficiency fall-off below 355 nm
Solution Approach 2:
The patent introduces a birefringent filter as an intermediary optical element between the frequency-doubling and sum-frequency mixing stages. This filter serves multiple functions: selecting the fundamental wavelength, polarizing the fundamental radiation, and rotating the polarization of second-harmonic radiation to match the fundamental radiation polarization, thereby enabling efficient type-I sum-frequency mixing
2Productivity
If type-I sum-frequency mixing is used to generate third-harmonic radiation at wavelengths as low as 280 nm, then the efficiency is maintained, but an additional birefringent optical element is necessary to align polarization orientations
Solution Approach 1:
The patent makes the birefringent filter multi-functional by designing it to simultaneously perform three functions: (1) select the fundamental wavelength from the OPS gain bandwidth, (2) polarize the fundamental radiation in a specific orientation, and (3) rotate the polarization of the second-harmonic radiation to align with the fundamental radiation. This consolidates multiple optical functions into a single element, reducing overall device complexity
3Ease of operation
If multiple birefringent elements are used in the laser-resonator, then the polarization control is achieved, but the cost increases for bio-instrumentation applications
Solution Approach 1:
The patent merges the functions of multiple separate birefringent elements into a single integrated birefringent filter. Instead of using separate elements for wavelength selection, polarization, and polarization rotation, all these functions are combined into one optical component, thereby reducing the total number of elements and associated costs
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 design enhances the efficiency of third-harmonic generation at wavelengths as low as 280 nm while reducing the number of birefringent elements, thereby lowering costs and improving the performance of OPS lasers in bio-instrumentation applications.
Implementation Method 1
A birefringent filter is provided and located in the laser-resonator between the first and second optically nonlinear crystals. The birefringent filter is arranged to select the fundamental wavelength from within a gain-bandwidth of the optically-pumped semiconductor gain-structure and to cause the circulating fundamental-wavelength radiation to be plane-polarized in a first polarization-orientation.
Implementation Method 2
The first optically nonlinear crystal is arranged to generate from the plane-polarized fundamental-wavelength radiation second-harmonic radiation that is plane-polarized in a second polarization-orientation. This arrangement provides that the fundamental radiation and second-harmonic radiation automatically have the relative orientations required for type-II sum-frequency mixing.
Implementation Method 3
The birefringent filter is further arranged to pass the fundamental-wavelength radiation with the polarization-orientation unchanged and to rotate the polarization-orientation of the second-harmonic radiation from the second polarization-orientation to about the first polarization-orientation.
Implementation Method 4
The second optically nonlinear crystal is arranged to generate third-harmonic radiation from the circulating fundamental-wavelength radiation and the polarization-rotated second-harmonic radiation.
Data Source
AI summary
An intra-cavity frequency-tripled OPS laser has a laser-resonator including two optically nonlinear crystals arranged for type-I frequency conversion. One of the crystals generates horizontally polarized second-harmonic radiation from vertically plane-polarized fundamental-wavelength radiation circulating in the laser-resonator. A birefringent filter is located between the optically nonlinear crystals. The birefringent filter selects the fundamental-wavelength, establishes the vertical polarization-orientation, and selectively rotates the polarization-orientation of the second-harmonic radiation from horizontal to vertical. The vertically polarized fundamental and second-harmonic radiations are type-I sum-frequency mixed by the other optically nonlinear crystal.