Aperture Stop Stabilizes OPS-Laser Output Power
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Solution Overview
Problem
The output power variation of external cavity, surface-emitting, optically pumped semiconductor-lasers (OPS-lasers) is erratic and unstable when the resonator length is adjusted, making it difficult to optimize the laser output due to potential misalignment of the circulating beam with the pump-spot.
Innovation Solution
Incorporating an aperture stop in the laser resonator, configured to stabilize the output by ensuring the pump radiation forms a circular spot on the OPS-structure and using birefringent filters and nonlinear crystals to select and generate harmonic wavelengths, while an optically nonlinear crystal with a truncated prismatic form functions as a polarizer to minimize birefringence interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the resonator length is adjusted to optimize output power, then the laser output can be maximized, but the output power variation becomes erratic and unstable due to misalignment of the circulating beam with the pump-spot
Solution Approach 1:
An aperture stop is introduced as an intermediary element in the resonator to mediate between the circulating beam and the pump-spot. The aperture stop ensures proper spatial filtering and alignment, allowing the beam to remain properly positioned on the gain-structure throughout resonator length adjustments, thereby eliminating erratic output variations while maintaining optimization capability
2Power
If the resonator is detuned to allow lateral modes to oscillate for higher power extraction, then more power can be extracted from the laser, but the single-mode output quality is compromised
Solution Approach 1:
The aperture stop creates local quality constraints within the resonator by providing spatial filtering at a specific location. This local intervention allows the system to maintain TEM00 mode quality at the aperture plane while still permitting power extraction, as the aperture enforces mode selectivity without requiring complete resonator detuning
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 smooths the variation in output power with resonator length, facilitating optimization and increasing temporal stability of the laser output, allowing for more accurate determination of the optimal resonator length.
Implementation Method 1
An aperture stop is incorporated in the laser resonator. The aperture stop can be a simple disc with a central aperture formed therein.
Implementation Method 2
A birefringent filter is located in the laser resonator and is arranged to select the fundamental wavelength from the gain-bandwidth of the gain-structure.
Implementation Method 3
A birefringent, optically nonlinear crystal is located in the laser resonator and is arranged to generate second-harmonic wavelength radiation from the fundamental wavelength radiation.
Implementation Method 4
The second optically nonlinear crystal has a longitudinal axis and has entrance and exit faces thereof non-orthogonally inclined to the longitudinal axis thereof such that the second optically nonlinear crystal has a truncated prismatic form. This prismatic form causes the second optically nonlinear crystal to function as a polarizer for the fundamental-wavelength radiation, and thereby minimizes interaction of the birefringence of the first optically nonlinear crystal with that of the birefringent filter.
Data Source
AI summary
An optically pumped semiconductor-laser (OPS-laser) resonator includes an arrangement for delivering optical pump radiation on an OPS-chip to cause fundamental radiation to circulate in the resonator. The resonator includes second and third-harmonic generating crystals and is arranged deliver third-harmonic radiation. The resonator also includes a stop positioned and configured to stabilize the laser output. The pump radiation arrangement delivers the pump radiation at an angle to the resonator axis and includes wedged GRIN lens arranged such that the pump radiation forms a circular spot on the OPS chip. The third harmonic generating crystal acts as a polarizer for the fundamental radiation and angularly separates fundamental and third harmonic beams.