Pulse width control of laser pulse control technology
The pulse control of laser is one of the key links in laser technology, which directly affects the performance and application effect of laser. This paper will systematically sort out the pulse width control, pulse frequency control and related modulation technology, and strive to be professional, comprehensive and logical.
1. Concept of pulse width
The Pulse Width of the laser refers to the duration of the laser pulse, which is a key parameter to describe the time characteristics of the laser output. For ultra-short pulse lasers (such as nanosecond, picosecond and femtosecond lasers), the shorter the pulse width, the higher the peak power, and the smaller the thermal effect, which is suitable for precision machining or scientific research.
2. Factors affecting the laser pulse width The pulse width of the laser is affected by a variety of factors, mainly including the following aspects:
a. Characteristics of the gain medium. Different types of gain media have unique energy level structure and fluorescence lifetime, which directly affect the generation and pulse width of the laser pulse. For example, solid-state lasers, Nd:YAG crystals and Ti:Sapphire crystals are common solid-state laser media. Gas lasers, such as carbon dioxide (CO₂) lasers and helium-neon (HeNe) lasers, usually produce relatively long pulses due to their molecular structure and excited state properties; Semiconductor lasers, by controlling the carrier recombination time, can achieve pulse widths ranging from nanoseconds to picoseconds.
The design of the laser cavity has a significant impact on the pulse width, including: the length of the cavity, the length of the laser cavity determines the time required for light to travel once and again in the cavity, a longer cavity will lead to a longer pulse width, while a shorter cavity is conducive to the generation of ultra-short pulses; Reflectance: A reflector with high reflectance can increase the photon density in the cavity, thereby improving the gain effect, but too high reflectance may increase the loss in the cavity and affect the pulse width stability; The position of the gain medium and the position of the gain medium in the cavity will also affect the interaction time between the photon and the gain medium, and then affect the pulse width.
c. Q-switching technology and mode-locking technology are two important means to realize pulse laser output and pulse width regulation.
d. Pump source and pump mode The power stability of the pump source and the choice of the pump mode also have an important impact on the pulse width.
3. Common pulse width control methods
a. Change the working mode of the laser: the working mode of the laser will directly affect its pulse width. The pulse width can be controlled by adjusting the following parameters: the frequency and intensity of the pump source, the energy input of the pump source, and the degree of particle population inversion in the gain medium; The reflectivity of the output lens changes the feedback efficiency in the resonator, thus affecting the pulse formation process.
b. Control pulse shape: indirectly adjust the pulse width by changing the shape of the laser pulse.
c. Current modulation: By changing the output current of the power supply to regulate the distribution of electronic energy levels in the laser medium, and then change the pulse width. This method has a fast response speed and is suitable for application scenarios that require rapid adjustment.
d. Switch modulation: by controlling the switching state of the laser to adjust the pulse width.
e. Temperature control: temperature changes will affect the electron energy level structure of the laser, thereby indirectly affecting the pulse width.
f. Use modulation technology: Modulation technology is an effective means of accurately controlling pulse width.
Laser modulation technology is a technology that uses laser as a carrier and loads information onto it. According to the relationship with the laser can be divided into internal modulation and external modulation. Internal modulation refers to the modulation mode in which the modulated signal is loaded in the process of laser oscillation to change the laser oscillation parameters and thus change the laser output characteristics. External modulation refers to the modulation mode in which the modulation signal is added after the laser is formed, and the output laser properties are changed without changing the oscillation parameters of the laser.
Modulation technology can also be classified according to carrier modulation forms, including analog modulation, pulse modulation, digital modulation (pulse code modulation); According to the modulation parameters, it is divided into intensity modulation and phase modulation.
Intensity modulator: The pulse width is controlled by adjusting the change of laser light intensity.
Phase modulator: The pulse width is adjusted by changing the phase of the light wave.
Phase-locked amplifier: Through the phase-locked amplifier modulation, the laser pulse width can be accurately adjusted.
Post time: Mar-24-2025