Q-switched Laser System Preventing Beam Seeding
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Solution Overview
Problem
Q-switched lasers are susceptible to spatial and spectral beam seeding due to pre-lase, leading to beam fragmentation and increased peak power density, which can cause damage to sensitive optics, and existing methods to prevent this either reduce output energy or are difficult to implement effectively.
Innovation Solution
Delaying the Q-switch trigger by an integer number of laser resonator lifetimes after the end of the pump pulse prevents pre-lase from causing beam seeding, ensuring the laser can operate closer to the damage threshold of optics without risking catastrophic damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-lase is allowed to occur, then spectral seeding can be achieved to control output frequency, but spatial beam seeding occurs causing beam fragmentation and excessive peak power density
Solution Approach 1:
The patent applies preliminary action by deliberately allowing pre-lase to occur during a defined time period after the pump pulse, then using a Q-switch to abruptly terminate it. This controlled preliminary action enables spectral seeding benefits while preventing the harmful spatial beam seeding that would occur if pre-lase were completely prevented or left uncontrolled.
Solution Approach 2:
The patent employs periodic action through the Q-switch mechanism, which periodically changes the resonator quality factor. The Q-switch remains closed during the pre-lase period, then opens at a predetermined time to terminate pre-lase and initiate the main laser pulse, creating a periodic control pattern that manages both spectral seeding and spatial beam quality.
2Object-affected harmful factors
If pre-lase is completely prevented by under-pumping, then spatial beam seeding is avoided, but output energy is reduced
Solution Approach 1:
Instead of under-pumping to prevent pre-lase, the patent uses preliminary action by allowing pre-lase to occur and then deliberately terminating it with a Q-switch. This approach maintains full pump energy while preventing spatial beam seeding, thereby preserving output energy that would otherwise be lost through under-pumping.
Solution Approach 2:
The Q-switch acts as an intermediary element that mediates between the pump energy and the laser output. It allows the system to fully utilize pump energy by permitting pre-lase, then intervenes to terminate pre-lase and transfer energy to the main pulse, avoiding both spatial beam seeding and energy loss.
3Use of energy by moving object
If the Q-switch is triggered immediately after the pump pulse, then output energy is maximized, but pre-lase causes spatial beam seeding and beam fragmentation
Solution Approach 1:
The patent applies preliminary action by introducing a controlled delay period after the pump pulse during which pre-lase is allowed to occur. The Q-switch is triggered after this predetermined time interval, which prevents spatial beam seeding while maintaining high output energy by utilizing the full pump energy reservoir.
Solution Approach 2:
The Q-switch creates a periodic control pattern by remaining closed during the pre-lase period and then opening at a predetermined time. This periodic action separates the pre-lase phase from the main pulse generation, ensuring stable beam spatial structure while maximizing energy transfer.
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 eliminates the risk of spatial and spectral beam seeding, protecting optics and allowing for simplified system design by preventing the increase in peak power density associated with pre-lase, while maintaining nearly full output energy.
Implementation Method 1
a laser system comprising a diode laser for pumping to produce a defined pump pulse, a gain medium to be pumped by the pump pulse
Implementation Method 2
a Q-Switch to trigger at a predetermined time after the start of the pump pulse to produce a main Q-Switch output pulse
Implementation Method 3
This can be forced to occur, for example, by permitting some leakage through the Q-switch itself
Data Source
AI summary
A method for preventing spatial or spectral beam seeding in a Q-switched laser is described. The Q-switch trigger of the laser is delayed by several laser resonator lifetimes after the end of the pump pulse. In this way, beam seeding is completely eliminated whilst pre-lase is maintained. The method described may be used for any laser system where the fall time of the pump radiation is sufficiently fast with respect to the upper state lifetime of the laser medium.