CW-Pumped Multi-Pass Amplifier for High-Energy Laser Pulses
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Solution Overview
Problem
Current technologies for generating high-energy electromagnetic radiation pulses struggle to achieve high pulse energies and repetition rates suitable for industrial material processing applications while maintaining spatial beam quality and stability, often resulting in thermal issues and complex setups.
Innovation Solution
A compact, continuously pumped multi-pass amplifier system with an optical switch placed outside the cavity, using a seed laser oscillator and multiple gain elements to achieve high pulse energies and tunable repetition rates without altering geometrical parameters, ensuring robustness and clean spatial mode properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the repetition rate of the initial oscillator is decreased to increase pulse energy, then pulse energy increases, but the oscillator becomes physically very large or requires complex folding technique which results in optical loss and reduced mechanical stability
Solution Approach 1:
The system segments the pulse train by using an optical switch to select only one pulse from a high repetition rate oscillator output. This allows the oscillator to maintain a high repetition rate and compact size while the selected pulse is amplified to high energy levels, resolving the contradiction between pulse energy and device complexity
Solution Approach 2:
An optical switch is introduced as an intermediary component between the oscillator and amplifier. The switch selects individual pulses from the high repetition rate train and directs them to the amplifier, enabling high pulse energy output without requiring the oscillator itself to operate at low repetition rates, thus maintaining oscillator compactness and stability
2Power
If multiple amplification stages are applied to achieve high average power, then average output power increases, but pulse energies remain below 1 μJ due to high repetition rate of the initial oscillator
Solution Approach 1:
The system uses periodic pulse selection through an optical switch operating at a lower repetition rate than the oscillator. By selecting one pulse from every N oscillator pulses (where N is the ratio of oscillator repetition rate to switch repetition rate), the system achieves high pulse energy while maintaining reasonable average power output
Solution Approach 2:
The optical switch performs preliminary selection of individual pulses from the high repetition rate train before they enter the amplification stage. This preliminary action ensures that only single, well-separated pulses are amplified, allowing each pulse to accumulate sufficient energy while the average power remains controlled
3Use of energy by moving object
If high average power is used to achieve high pulse energy, then pulse energy increases, but thermal fracture and thermal lens effects occur
Solution Approach 1:
The system employs periodic, low-duty-cycle pulsing where the optical switch selects individual pulses at a repetition rate that allows sufficient cooling time between pulses. This periodic operation with low average power prevents thermal accumulation in the gain medium, avoiding thermal fracture and lens effects while still achieving high peak pulse energies
Solution Approach 2:
The amplification process is segmented into discrete, widely-spaced pulse events rather than continuous high-power operation. By amplifying individual selected pulses with long intervals between them, the system achieves high pulse energy without sustained thermal loading that would cause thermal damage
4Use of energy by moving object
If the oscillator cavity length is increased to decrease repetition rate, then pulse energy increases, but the oscillator becomes physically very large
Solution Approach 1:
The system segments the high repetition rate pulse train using an optical switch, allowing the oscillator to maintain a short cavity length and high repetition rate while the switch selects individual pulses for amplification. This eliminates the need to increase cavity length to reduce repetition rate
Solution Approach 2:
The optical switch acts as an intermediary that decouples the oscillator repetition rate from the output pulse repetition rate. The oscillator can operate at high frequency with short cavity, while the switch reduces the effective output repetition rate, allowing high pulse energy without increasing cavity length
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 allows for high-energy pulse generation with stable repetition rates between 50 kHz and 25 MHz, achieving pulse energies up to several microjoules and maintaining excellent spatial beam quality, suitable for advanced material processing and nonlinear optics applications.
Implementation Method 1
an optical switch operable outside the cavity at a repetition rate lower than the repetition rate of the laser oscillator for coupling individual pulses from the train of laser pulses into the amplifier
Implementation Method 2
a radiation amplifier comprising a gain element and second pumping means for continuously pumping the gain element with pump radiation at a pump wavelength
Implementation Method 3
continuously pumped amplifier system with an optical switch placed outside the cavity, using a seed laser oscillator and multiple gain elements to achieve high pulse energies and tunable repetition rates without altering geometrical parameters
Data Source
Figure 1~3
Figure 4~6
Figure 7~8
AI summary
An apparatus for generating electromagnetic radiation pulses comprises a mode-locked laser oscillator with an oscillator cavity defining an oscillator beam path, a first gain element (2), first pumping means for pumping said first gain element, and a mode locker, and being operable to produce a train of seed electromagnetic radiation pulses (5). Further an optical switch (11) is placed outside of the oscillator beam path (5) and is arranged in a beam path of radiation coupled out from the oscillator, the optical switch (11) operable to couple radiation from a switch input into a switch output during a certain time period or certain time periods. A radiation amplifier is arranged in a beam path of radiation radiated from the switch output. The amplifier includes a second gain element (14) and second pumping means, the second pumping means comprising a continuous-wave pump radiation source.