Photoelastic Modulator Laser Beam Splitting for Power Density
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Solution Overview
Problem
Splitting a pulsed laser beam into two paths using existing methods results in reduced power density and focal point deviation, leading to inadequate machining and short condenser life due to thermal lens effects.
Innovation Solution
A laser machining apparatus employing a photoelastic modulator with a piezo element and synthetic quartz to split the pulsed laser beam alternately every pulse, maintaining power density and preventing focal point deviation by using high-frequency voltage matching the natural frequency of the synthetic quartz, along with half and quarter wavelength plates and a polarization beam splitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If a pulsed laser beam is split into two paths using a polarization beam splitter, then beam path separation is achieved, but power density is reduced by half
Solution Approach 1:
The patent employs a photoelastic modulator that operates at a specific frequency to periodically switch the polarization state of the laser beam. This periodic modulation allows the beam to be directed alternately to different paths while maintaining full power density in each pulse, rather than splitting the power continuously. The key is that each pulse maintains its original power while the temporal modulation enables path separation.
2Adaptability or versatility
If a pulsed laser beam is transmitted through a small diameter modulator, then beam splitting is achieved, but thermal lens effect causes focal point deviation
Solution Approach 1:
The patent changes the operating parameters by using a photoelastic modulator with a relatively large effective diameter (several cm) compared to conventional EOMs/AOMs. This parameter change allows the laser beam to be transmitted with lower density, preventing thermal lens effects and maintaining focal point stability while still achieving beam splitting through polarization modulation.
3Extent of automation
If EOM or AOM is used to split laser beam in synchronism with repetition frequency, then beam splitting is achieved, but output power is reduced by 15 to 30%
Solution Approach 1:
The patent selects a photoelastic modulator based on synthetic quartz as the beam splitting component. This material choice provides high transmittance and resistance to thermal lens effects, maintaining output power while achieving the required synchronized beam splitting functionality. The synthetic quartz-based PEM offers superior durability and performance compared to conventional EOM/AOM components.
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
Ensures proper machining with no reduction in power density and prevents thermal lens effects, extending the life of the condenser by maintaining a stable focal point and high transmittance.
Implementation Method 1
The beam splitting means includes a photoelastic modulator that has a piezo element and a synthetic quartz formed in one piece. The photoelastic modulator modulates the laser beam so that a polarization plane of the laser beam is alternately at 0 and 90 degrees by applying, to the piezo element, a high frequency voltage at a frequency that matches the natural frequency of the synthetic quartz.
Implementation Method 2
The beam splitting means includes a photoelastic modulator that has a piezo element and a synthetic quartz formed in one piece. The photoelastic modulator modulates the laser beam so that a polarization plane of the laser beam is alternately at 0 and 90 degrees by applying, to the piezo element, a high frequency voltage
Implementation Method 3
The laser beam irradiation means includes laser beam oscillation means and a condenser. The laser beam oscillation means oscillates a laser beam. The condenser includes a condenser lens adapted to collect the laser beam oscillated by the laser beam oscillation means and irradiate the beam onto the workpiece
Implementation Method 4
a technique has been proposed which splits a pulsed laser beam every pulse in synchronism with the repetition frequency of the pulsed laser beam using an electro optical modulator (EOM) or accousto optical modulator (AOM)
Data Source
AI summary
A laser machining apparatus has a laser beam irradiation unit that includes: a pulsed laser oscillator that oscillates a pulsed laser beam at a given repetition frequency; first and second condensers that collect the pulsed laser beam oscillated by the pulsed laser oscillator; and a beam splitting unit arranged between the pulsed laser oscillator and the first and second condensers to split the pulsed laser beam oscillated by the pulsed laser oscillator and direct the resultant beams alternately toward the first and second condensers. The beam splitting unit includes a photoelastic modulator that has a piezo element and a synthetic quartz formed in one piece and modulates the laser beam so that a polarization plane of the laser beam is alternately at 0 and 90 degrees by applying, to the piezo element, a high frequency voltage at a frequency that matches the natural frequency of the synthetic quartz.