Injection-Locked Pulsed Laser Error Signal Detection via Saturated Photodiode
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Solution Overview
Problem
High-power pulsed lasers face challenges in achieving single-frequency operation due to the difficulty in obtaining an error signal for injection locking, as the pulse light power is much greater than the seed light power and the modulation signal is minimal, making it hard to lock the cavity length effectively.
Innovation Solution
A high-power single-frequency pulsed laser system utilizing a light detector with pulse saturation current characteristics, including a photodiode, trans-impedance amplifier, and servo control system, which processes the probe light to extract an error signal and adjust the cavity length, thereby overcoming the power imbalance and achieving injection locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a frequency selective element is inserted in the cavity to reduce linewidth, then the spectral width is narrowed, but the intracavity loss increases and power level decreases
Solution Approach 1:
The patent uses a frequency selective element as an intermediary component within the optical cavity to achieve spectral narrowing. This element acts as a mediator that selectively transmits the desired frequency while blocking others, thereby reducing linewidth without requiring direct modification of the laser gain medium. The frequency selective element serves as a bridge between the broad-spectrum laser output and the narrow-linewidth requirement.
2Measurement precision
If frequency selective element is used to achieve single-frequency output, then the spectral purity is improved, but the element may be damaged by high peak power
Solution Approach 1:
The patent segments the laser system into distinct functional components: a high-power laser source, a frequency selective element for spectral purification, and a detection system. By separating the high-power generation function from the spectral selection function, the system allows the frequency selective element to operate at lower effective power levels while the main laser operates at high power, thus protecting the sensitive frequency selective element from damage.
3Loss of energy
If injection locking method is used to simplify cavity structure and reduce loss, then the laser output threshold is lowered, but the error signal extraction becomes difficult due to power imbalance
Solution Approach 1:
The patent introduces a photodetector as an intermediary device that converts the optical error signal into an electrical signal for processing. This intermediary conversion allows the weak modulated seed light signal to be detected and processed separately from the high-power pulsed laser light, solving the detection difficulty caused by the large power imbalance between the seed light and the pulsed laser output.
4Power
If the pulse light power is much greater than the seed light power, then the laser output power is high, but the modulation signal becomes minimal and cannot be obtained
Solution Approach 1:
The patent applies preliminary modulation to the seed light before injection into the laser cavity. By pre-modulating the seed light with the desired frequency information, the modulation signal is embedded in the low-power seed light before it encounters the high-power pulsed laser. This preliminary action ensures that the modulation information is preserved and can be extracted later, even though the final output is dominated by the high-power pulsed laser.
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 effectively improves the signal-to-noise ratio and enables stable single-frequency operation by saturating the pulse current and unsaturating the modulated seed current, allowing for precise control of the cavity length and outputting high-power single-frequency pulsed lasers with improved stability.
Implementation Method 1
a light detector with pulse saturation current characteristics... the light detector has the characteristic of saturation current, and after the probe light enters the light detector, the pulse current becomes saturated and the modulated seed current becomes unsaturated
Data Source
AI summary
The present application discloses a high-power single-frequency pulsed laser based on an injection locking technology, including a pump light supply device, a seed light supply device, a slave laser, a light detector and a servo control system. The servo control system receives a probe signal outputted by the light detector and controls the cavity length of the slave laser according to an error signal extracted from the probe signal. The light detector has the characteristic of saturation current, and after the probe light enters the light detector, the pulse current becomes saturated and the modulated seed current becomes unsaturated. According to the present application, a light detector with pulse saturation current characteristics is adopted to effectively avoid the problem that the error signal cannot be obtained and it is difficult to achieve injection locking.