Picosecond Optical Pulse Burst Generation via Phase Modulation
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Solution Overview
Problem
Current technologies lack efficient and versatile methods for generating pulse train bursts of picosecond optical pulses, particularly for industrial applications like material micro-machining, as existing systems struggle with fine-tuning pulse repetition rates and durations, and fail to provide high energy and near diffraction-limited beam quality.
Innovation Solution
A method and device that generate bursts of optical sub-pulses by creating seed pulses, imposing periodic phase modulation to spread their spectral profiles, and spectrally filtering to retain selected components, allowing for flexible control of pulse duration, repetition rate, and spectral characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mode-locked fiber lasers are used to generate picosecond pulses at high repetition rates, then pulse generation capability is improved, but timing between successive pulses cannot be adjusted arbitrarily and is determined by harmonics of the laser cavity
Solution Approach 1:
The invention segments the pulse train by using a pulse picker that selects specific pulses from the mode-locked laser output. This allows arbitrary timing between successive pulses by choosing which pulses to transmit, resolving the contradiction between maintaining high repetition rate generation and achieving flexible timing adjustment.
Solution Approach 2:
The invention introduces a pulse picker as an intermediary device between the mode-locked laser and the output. This mediator component enables flexible pulse timing selection without modifying the original laser cavity harmonics constraint, allowing arbitrary timing adjustment while preserving the high repetition rate generation capability.
2Manufacturing precision
If femtosecond lasers are used for cold ablation, then processing quality is improved, but system complexity and cost increase
Solution Approach 1:
The invention changes the pulse duration parameter from femtosecond to picosecond range, and uses pulse train bursts with specific timing characteristics to achieve cold ablation effects. This parameter change allows obtaining similar processing quality with simpler, less expensive picosecond laser systems rather than complex femtosecond lasers.
Solution Approach 2:
The invention employs periodic pulse train bursts with controlled repetition rates and duty cycles to achieve cumulative heating effects that enable cold ablation. This periodic action pattern allows picosecond lasers to achieve processing quality comparable to femtosecond lasers while maintaining lower system complexity.
3Productivity
If nanosecond pulses are used for thermal ablation, then material removal rate is improved, but heat-affected zone increases causing collateral damage
Solution Approach 1:
The invention segments the nanosecond pulse into multiple picosecond sub-pulses within a burst structure. This segmentation allows the energy to be delivered in controlled increments that achieve material removal comparable to nanosecond pulses while limiting the heat-affected zone through the shorter individual pulse durations.
Solution Approach 2:
The invention changes the pulse duration parameter from nanosecond to picosecond range while using burst mode operation. This parameter change enables achieving high material removal rates through cumulative effect of multiple pulses while the shorter individual pulse duration prevents excessive heat diffusion and collateral damage.
4Productivity
If pulse train bursts are used to combine cold and thermal ablation benefits, then processing efficiency is improved, but control over pulse temporal profile becomes more complex
Solution Approach 1:
The invention uses dynamic control parameters including burst repetition rate, pulse repetition rate within bursts, and duty cycle to optimize the temporal profile. These dynamic parameters allow flexible adjustment of the pulse train characteristics to match specific processing requirements while maintaining processing efficiency through the combined cold and thermal ablation benefits.
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
Enables efficient and versatile generation of picosecond optical pulse train bursts with tailored temporal and spectral parameters, suitable for high-power applications like micromachining, offering improved processing speed and quality with reduced collateral damage.
Implementation Method 1
imposing a periodic phase modulation on the seed pulses, the periodic phase modulation having a modulation frequency and a modulation amplitude jointly selected to spread the spectral profile of each of the seed pulses over a plurality of time-dependent spectral components
Implementation Method 2
spectrally filtering each of the seed pulses to retain therein only selected ones of the time-dependent spectral components, the filtering creating gaps in the amplitude profile of the seed pulses
Implementation Method 3
generating seed optical pulses each having a pulse duration, an amplitude profile and a spectral profile
Data Source
AI summary
A method and device are provided for generating bursts of sub-pulses, preferably in the picosecond range. Seed pulses are first generated, and then phase modulated to spread their spectral profile to several time-dependent spectral components. The phase modulated seed pulses are then spectrally filtered to remove spectral components and retain only selected ones, creating gaps in the amplitude profile of the seed pulses which therefore form bursts of sub-pulses. Various parameters such as the modulation amplitude, the modulation frequency, the spectral characteristics of the filters and the overall amplitude of the seed pulses may be controlled to provide a great versatility and adaptability.