Q-switched mode-locked (QML) lasers are a type of laser that combines Q-switching and mode-locking techniques to generate ultra-short pulses with high peak power. In this article, we will discuss the construction and operation of a Q-switched mode-locked diode-pumped Nd:YVO4 laser with a saturable Bragg reflector (SBR), focusing on its design principles, working mechanism, and applications.
The QML laser system consists of several key components:
Nd:YVO4 Crystal: This is the gain medium of the laser, which is pumped by a laser diode to generate the lasing action.
Saturable Bragg Reflector (SBR): The SBR is a mirror with variable reflectivity, which acts as both a Q-switch and a mode-locker in the laser cavity. It allows the laser to switch between Q-switched and mode-locked operation.
Laser Diode Pump: The laser diode provides the optical pump power to excite the Nd:YVO4 crystal, causing it to emit laser light.
Output Coupler: This is a partially reflective mirror that allows a portion of the laser light to exit the cavity, forming the output beam.
Q-switch Driver and Mode-locker Driver: These drivers control the operation of the Q-switch and mode-locker, respectively, by applying electrical signals to the SBR.
Q-switched Operation: In Q-switched mode, the SBR has high reflectivity, trapping photons in the cavity to build up energy. When the Q-switch driver applies a high-voltage pulse to the SBR, its reflectivity decreases rapidly, allowing the accumulated photons to be released as a short, high-energy pulse.
Mode-locked Operation: In mode-locked mode, the SBR has low reflectivity, allowing light to pass through it multiple times and build up in phase. The mode-locker driver applies a periodic signal to the SBR, causing it to modulate the laser light and generate a train of ultra-short pulses.
Micro-machining: The ultra-short pulses generated by the QML laser are ideal for precision micro-machining of materials such as metals, ceramics, and polymers.
Biomedical Imaging: The high peak power of the QML laser makes it suitable for applications in biomedical imaging, such as multiphoton microscopy and optical coherence tomography.
Laser Spectroscopy: The short pulse duration of the QML laser enables high-resolution spectroscopy in fields such as environmental monitoring and chemical analysis.
Lidar Systems: The high-energy pulses of the QML laser are used in lidar systems for remote sensing applications, such as atmospheric monitoring and terrain mapping.
In conclusion, the Q-switched mode-locked diode-pumped Nd:YVO4 laser with a saturable Bragg reflector is a versatile and powerful laser system that can generate ultra-short pulses with high peak power. Its unique design and operation make it well-suited for a wide range of applications in science, industry, and medicine.
