Kerr Lens Mode-Locking with Separated Loss-Modulation Device
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Solution Overview
Problem
Conventional methods for generating laser pulses by Kerr lens mode-locking face limitations in achieving simultaneous large modulation bandwidth and power scalability, particularly at high intra-cavity peak powers, due to nonlinear effects and self-focusing issues within acousto-optic modulators.
Innovation Solution
A laser device with a resonator design that separates the Kerr medium from the gain medium, utilizing a loss-modulation device with a modulation medium that introduces a Kerr effect and modulates power loss, allowing for stable Kerr lens mode-locking with enhanced modulation bandwidth and power scalability by decoupling nonlinearity from the gain medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an acousto-optic modulator is placed inside the cavity for intra-cavity loss modulation, then the modulation bandwidth can be increased, but self-focusing (Kerr lensing) inside the AOM counteracts the main KLM mechanism and deteriorates mode-locking performance
Solution Approach 1:
The patent extracts the Kerr medium function from the acousto-optic modulator by using a separate dedicated Kerr medium (such as a nonlinear optical crystal or glass) positioned in the cavity, while the AOM is used solely for loss modulation. This separation eliminates the harmful self-focusing effect within the modulator while preserving both the fast modulation bandwidth and the Kerr lens mode-locking mechanism.
Solution Approach 2:
The patent segments the functional roles within the laser cavity by dividing the system into distinct components: one element (AOM) dedicated to loss modulation and another element (separate Kerr medium) dedicated to providing the Kerr effect. This functional segmentation allows each component to operate optimally without interfering with the other's performance.
2Object-affected harmful factors
If the beam diameter is increased to reduce nonlinear phase-shift inside the AOM, then the contribution of nonlinear refractive index becomes important and self-focusing effects increase at high powers
Solution Approach 1:
The patent extracts the Kerr effect generation from the AOM by introducing a separate Kerr medium with appropriate nonlinear optical properties. This allows the beam parameters to be optimized independently: the beam can be kept sufficiently narrow to minimize nonlinear phase-shift in the AOM while the separate Kerr medium provides the necessary Kerr effect without significant self-focusing issues.
3Object-affected harmful factors
If the spot-size inside the AOM is increased to mitigate nonlinear effects, then the transit time increases which is linearly proportional to the beam radius and reduces modulation bandwidth
Solution Approach 1:
The patent extracts the Kerr medium function from the AOM, allowing the beam spot-size inside the AOM to be kept small for fast modulation (short transit time) while the Kerr effect is provided by a separate medium where the beam can be focused appropriately without compromising modulation bandwidth.
4Reliability
If pump power modulation is used for CEO stabilization, then the accessible modulation bandwidth is limited by the coupling between gain and pulse energy determined by the upper-state lifetime of the gain medium
Solution Approach 1:
The patent replaces pump power modulation with intra-cavity loss modulation using an acousto-optic modulator. This substitution bypasses the limitation imposed by the gain medium's upper-state lifetime, enabling CEO stabilization at modulation bandwidths determined by the AOM's acoustic wave properties rather than the gain medium's relaxation time.
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
The solution enables stable pulse mode-locking with increased modulation bandwidth and power scalability, maintaining efficient Kerr lens mode-locking performance even at high intra-cavity peak powers, while minimizing nonlinear phase-shifts and self-focusing effects.
Implementation Method 1
a Kerr medium device (30) with at least one Kerr medium, which is configured for creating the laser pulses from the laser light field by the nonlinear Kerr effect
Implementation Method 2
a loss-modulation device (optical modulator device) having a modulation medium (modulator material, modulator component), which is capable of modulating a power loss of the laser pulses generated in the laser resonator
Data Source
AI summary
A laser device (100), being configured for generating laser pulses by Ken lens based mode locking, comprises a laser resonator (10) with a plurality of resonator mirrors (11.1, 11.2, 11.3) spanning a resonator beam path (12), a solid state gain medium (20) being arranged in the laser resonator (10), a Kerr medium device (30) being arranged with a distance from the gain medium (20) in the laser resonator (10), wherein the Kerr medium device (30) includes at least one Ken medium being arranged in a focal range of the resonator beam path and being configured for forming the laser pulses by the nonlinear Kerr effect, and a loss-modulation device (31, 32) having a modulator medium, which is capable of modulating a power loss of the laser pulses generated in the laser resonator (10), wherein the Kerr medium device (30) includes the modulator medium of the loss-modulation device (31, 32) as the at least one Kerr medium having an optical non-linearity being adapted for both of creating the Kerr lens based mode-locking in the laser resonator and modulating the power loss in the laser resonator. Furthermore, a method of generating laser pulses by Kerr lens based mode locking is described, wherein a loss-modulation device (31, 32) is used for both of introducing a Ken effect in the laser resonator (10) and modulating the power loss.