Source: Chinese Academy of Sciences

<>

Resonant Frequency Doubling in Nonlinear Crystals

Singly and Doubly Resonant Frequency Doubling

Resonant frequency doubling is a technique used to enhance the conversion efficiency of frequency doubling in nonlinear crystals. There are three versions of resonant frequency doubling:

Singly-Resonant Frequency Doubling

In singly-resonant frequency doubling, the pump wave is resonantly enhanced within the cavity, leading to increased conversion efficiency. This method allows for recycling of the remaining pump power in the laser resonator, resulting in high effective conversion efficiency.

Doubly-Resonant Frequency Doubling

Doubly-resonant frequency doubling involves making both the pump wave and the second-harmonic wave resonant in the cavity simultaneously. This technique can achieve high conversion efficiencies, especially for low pump powers, but requires careful stabilization of double resonance.

Mode Calculations

Software tools like RP Resonator can be used for calculating resonator mode properties and power enhancement factors.

Stabilization of Resonance

Automatic stabilization systems are necessary to maintain resonance during operation. Feedback systems like the Hänsch–Couillaud method or the Pound–Drever–Hall technique are commonly used to detect and correct deviations from resonance.

Mode Matching

Mode matching of the pump light to the resonator is essential for efficient frequency doubling. Gaussian laser beams are often used and matched to the fundamental mode of the resonator using optical elements like lenses and mirrors.

Resonator Designs

Ring resonators are commonly used for resonant frequency doubling. Impedance matching is crucial for achieving high conversion efficiencies. Monolithic resonators with dielectric mirror coatings can provide high stability and efficiency.

Frequency Doubling of Ultrashort Pulses

Resonant doubling can also be applied to ultrashort pulses from mode-locked lasers by ensuring resonance for all lines of the optical spectrum of the pulse train.

Resonator Sum and Difference Frequency Generation

Resonant nonlinear frequency conversion techniques can be extended to processes like sum and difference frequency generation, offering versatile applications in photonics.

Intracavity Frequency Doubling

Intracavity frequency doubling is an alternative method that automatically provides a resonant pump wave without the need for active frequency stabilization. It can be combined with resonant doubling for enhanced performance.

Conclusion

Resonant frequency doubling techniques play a vital role in enhancing the efficiency of frequency doubling in nonlinear crystals. By utilizing resonant cavities and advanced stabilization methods, researchers and engineers can achieve high conversion efficiencies and stable operation in various photonics applications.

Source: ResearchGate
Feel free to comment your thoughts.