Unstable Resonator Laser System for Sub-Nanosecond Pulse Generation
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Solution Overview
Problem
Current laser systems for generating high-energy, sub-nanosecond pulses are complex, unstable, and difficult to integrate, limiting their effectiveness in medical and aesthetic applications where precise fragmentation of biological tissues is required.
Innovation Solution
A compact laser system using an unstable resonator operating in Q-switching regime, combined with control electronics, to produce a pulse train with a main pulse of duration shorter than one nanosecond and high peak power, achieving a high-energy, stable, and repeatable output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional laser systems are used to generate high-energy pulses, then pulse energy can be achieved, but pulse duration becomes longer than sub-nanosecond and system complexity increases
Solution Approach 1:
The laser system pre-pumps the gain medium to a high energy state before the Q-switch releases the stored energy. This preliminary energy storage in the Nd:YAG crystal allows the system to generate sub-nanosecond pulses with high energy without requiring complex real-time control mechanisms during the pulse generation itself.
Solution Approach 2:
The patent introduces a Q-switch as an intermediary component that mediates between the continuously pumped laser medium and the output pulse. This Q-switch mechanism (using a Pockels cell or similar device) acts as a gate that suddenly opens to release the stored energy in a controlled sub-nanosecond burst, simplifying the overall system architecture compared to direct modulation approaches.
2Use of energy by moving object
If laser pulse duration is extended to increase energy delivery, then total energy increases, but peak power decreases and photoacoustic effect efficiency is reduced
Solution Approach 1:
The system changes the temporal parameter of energy delivery by using Q-switching to produce pulses with duration in the sub-nanosecond range (typically 100-500 ps). This parameter change allows the same total energy to be delivered in a much shorter time window, thereby increasing peak power by factors of 10-100 compared to conventional longer pulses, while maintaining or enhancing the photoacoustic effect efficiency.
3Manufacturing precision
If multiple complex components are used to achieve sub-nanosecond pulses, then pulse quality improves, but system stability and ease of integration deteriorate
Solution Approach 1:
The patent merges the pumping mechanism, gain medium, Q-switch, and resonator into a compact integrated laser system. By combining these components into a unified design with shared optical paths and synchronized control, the system achieves sub-nanosecond pulse quality while improving stability and ease of integration compared to systems using separate, loosely-coupled components.
Solution Approach 2:
The laser system incorporates feedback mechanisms through the optical resonator cavity, where the circulating light provides automatic feedback to the gain medium. This feedback ensures stable pulse generation by maintaining the correct phase and amplitude relationships, reducing sensitivity to component variations, and improving overall system reliability without requiring complex external control systems.
4Productivity
If high fluence is applied to reach deep tissue particles, then fragmentation effectiveness improves, but invasiveness and potential damage increase
Solution Approach 1:
The system uses periodic pulsed operation with sub-nanosecond duration to deliver energy in brief, intense bursts. This periodic action allows the tissue to cool and recover between pulses while accumulating the necessary energy for fragmentation. The short pulse duration confines the thermal and mechanical effects to the immediate treatment zone, reducing invasiveness and damage to surrounding healthy tissue while maintaining effectiveness for deep particle fragmentation.
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 system generates a highly energetic, stable pulse train with a high contrast between the main and secondary pulses, enhancing the photoacoustic effect for efficient fragmentation of particles of varying diameters with reduced invasiveness and increased efficiency in medical applications.
Implementation Method 1
an unstable resonator operating in Q-switching regime
Implementation Method 2
Interaction between the laser and the biological tissue may be of a photothermal type, when, that is, light energy is transformed into heat
Implementation Method 3
Rapid heating results in a violent expansion that generates an acoustic shock wave. Generation of the acoustic shock wave takes the name of 'photoacoustic effect'
Implementation Method 4
an unstable resonator operating in Q-switching regime, which comprises in succession a first mirror with high reflectivity, an electro-optical switch, a polarizer, a gain medium, and a second, output, mirror
Data Source
AI summary
A laser system for generating a series of laser pulses comprising a laser generator that supplies an injection pulse to an amplifier; said amplifier comprising: a gain medium enclosed between a first mirror and a second, output, mirror opposite to said first mirror; and an optical switch set in the proximity of said first mirror; said laser system being characterized in that said amplifier is an unstable laser resonator and said injection pulse is supplied to said laser resonator in synchronism with opening of said optical switch; said series of laser pulses comprises at least one pulse having a duration shorter than or equal to 2 ns and an energy higher than 100 mJ and at least three times higher than the energy of any other pulse of said series of pulses.