Semiconductor Laser External Cavity for Stimulated Brillouin Scattering
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Solution Overview
Problem
Existing laser light sources with optical fiber amplifiers suffer from undesirable nonlinear optical effects like stimulated Brillouin scattering, which reduce power output and can cause damage to components, especially at high spectral power densities.
Innovation Solution
A semiconductor laser with a partially transmitting wavelength selective light reflector and an external laser cavity is used to control the spectral density and duration of high-intensity periods, ensuring the roundtrip time in the external cavity is shorter than the build-up time of nonlinear optical effects, thereby reducing the likelihood of stimulated Brillouin scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high spectral power density is used in optical fiber amplifier, then power output is increased, but stimulated Brillouin scattering occurs causing power loss and component damage
Solution Approach 1:
The patent applies periodic pulsed operation of the seed laser with specifically controlled pulse widths (3 ns to 1 µs) and duty cycles. This temporal modulation ensures that the optical fiber amplifier receives light in periodic bursts rather than continuous high-intensity illumination, preventing the build-up of nonlinear effects like stimulated Brillouin scattering while maintaining high peak power output capability
Solution Approach 2:
The patent modifies the temporal parameters of light delivery by controlling pulse width, repetition rate, and duty cycle of the seed laser. These parameter changes transform the continuous high spectral power density into pulsed operation with reduced average power, thereby avoiding stimulated Brillouin scattering threshold while preserving high peak power for effective laser machining
2Object-affected harmful factors
If pulsed operation with short pulse duration is used, then nonlinear optical effects are reduced, but average power output is limited
Solution Approach 1:
The patent employs periodic pulsed operation where the seed laser delivers light in repeated bursts. By optimizing pulse width (3 ns to 1 µs) and duty cycle, the system achieves low average power during each pulse (avoiding nonlinear effects) while maintaining high peak power. The periodic repetition accumulates effective energy delivery over time, resolving the contradiction between short pulse duration and average power output
Solution Approach 2:
The patent ensures continuous useful action through high repetition rate pulsed operation. Although each individual pulse is short to avoid nonlinear effects, the high repetition rate ensures that energy is delivered continuously over time, maintaining high average power output. This creates an effective continuous process that benefits from both short pulse characteristics and sustained energy delivery
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 approach effectively reduces the occurrence of stimulated Brillouin scattering and other nonlinear effects, maintaining high power output and preventing damage to laser components.
Implementation Method 1
A laser light source comprises a semiconductor laser adapted for pulsed operation, a power source, and a partially transmitting wavelength selective light reflector
Implementation Method 2
laser radiation generated by a laser light source is made to interact with at least one workpiece to machine the at least one workpiece
Implementation Method 3
If light from a seed light source having a photon energy corresponding to an energy difference between the excited state and a dopant state having a lower energy than the excited state is supplied to the optical fiber, the light from the seed light source can be amplified by stimulated emission
Implementation Method 4
A wavelength of the pump light source may be adapted to an absorption wavelength of the dopants in the optical fiber such that the dopants absorb the light from the pump light source
Data Source
AI summary
A laser light source comprises a semiconductor laser adapted for pulsed operation, a partially transmitting wavelength selective light reflector. The semiconductor laser comprises a front facet and a back facet. The front facet and the back facet define an internal laser cavity. The internal laser cavity comprises a laser active medium. The partially transmitting wavelength selective light reflector has a peak reflectivity within a gain bandwidth of said laser active medium. The wavelength selective light reflector and the back facet define an external laser cavity. A roundtrip time of light in the external laser cavity is about 20 nanoseconds or less. A full width half maximum bandwidth of the wavelength selective light reflector is adapted to accommodate at least 12 longitudinal modes of the internal laser cavity and at least 250 longitudinal modes of the external laser cavity.