The main technical route of tunable narrow-linewidth lasers

The main technical route of tunable narrow-linewidth lasers

The main technical routes of tunable narrow-linewidth lasers with semiconductor outer cavities

Tunable narrow-linewidth lasers are the foundation for wide applications in fields such as atomic physics, spectroscopy, quantum information, coherent communication, remote sensing, and precision measurement. In these fields, simpler, cheaper, narrower linewidth and wider tuning range lasers will continue to drive new applications of this technology.

Over the past 50 years, the history of the tunable light source TLS Laser has largely reflected the development of laser technology. The initial dye lasers have been replaced by external cavity diode lasers (ECDLs), while high-power systems are dominated by tunable solid-state lasers (such as titanium-sapphire lasers) or frequency-converted Nd:YAG lasers using optical parametric oscillators (OPO). Diode lasers without stable outer cavities have filled the low-cost and low-performance market end with commercial DFB Laser and DBR diodes, with line widths as narrow as 500kHz. Recently, fiber lasers and variable-frequency fiber lasers have begun to replace many solid-state systems with different designs, offering higher power and greater tunability, or narrower line widths. Nowadays, the emergence of frequency combs enables frequency-stabilized lasers to be achieved at any wavelength while maintaining excellent stability and accuracy. However, despite this, the external cavity semiconductor laser still maintains its status as a commonly used light source in many laboratories due to its simplicity, multi-functionality, respectable performance and very low cost.

At present, tunable narrow-linewidth lasers with external cavity semiconductors have been widely applied in:

Laser cooling and capture

Bose-Einstein condensation

Quantum Optics: Compressed light

Electromagnetic transparent and slow light

Time and frequency standards

Laser spectroscopy

Tunable narrow-linewidth lasers are typically composed of a controller, a laser diode and a frequency selection module. For example, gratings used for laser frequency selection and tuning, or filters based on the cat’s eye structure, etc. The important characteristics of tunable narrow-linewidth lasers with external cavity semiconductors include narrow laser linewidth, low frequency drift, and wide tuning range, etc. And these outstanding characteristics depend on an extremely excellent laser drive circuit, the overall mechanical stability of the laser, and the principle of frequency selection. To achieve higher frequency stability of the laser, different types of laser frequency-locking modules can be added. For example, by using PDH frequency stabilization technology to lock the laser wavelength on the optical super-stable cavity, the linewidth of the laser can be narrowed to the level of 1 Hz, and the frequency stability can reach < 3× 10-15 @ 1 s.