The coupling of photon and phonon synchronization laser in the same cavity is explored in a two-domain laser with forward multimode stimulated Brillouin scattering

Figure: The working principle of a dual-domain fiber laser. (A) Schematic diagram of a two-domain (phonon and photon) laser based on forward intermodulation SBS in a TMF ring cavity. Dispersion diagram for (B) backward SBS and (C) forward SBS in an optical fiber under conservation of energy and momentum. (D) The working principle of both phonon and phonon laser generation is explained in the frequency domain. Source: Science Advances (2023). DOI: 10.1126/sciadv.adg7841

The laser is a major historical invention that has had a pervasive impact on society. The concept also has interdisciplinary applications, such as phonon lasers and atomic lasers. A laser in one physical domain can be pumped by energy in another physical domain. However, so far, all the lasers demonstrated in practice have only been lasers in one field of physics.

In a new report published in Science Advances, a research team demonstrates the simultaneous process of photon and phonon lasers. Dual-domain lasers have a variety of applications, such as optical tweezers and acoustic tweezers, for mechanical sensing, generating microwaves, and performing quantum processing. The team hopes this demonstration will open new avenues for multi-domain laser-related applications.

Two domain laser is developed

The laser is an extension of the microfrequency of the electronic oscillator in the radio frequency and the maser in the optical region. Lasers have huge applications with new expanded concepts across fields, such as acoustic oscillators, also known as sasers, and oscillators in atomic or matter waves. The concept of laser has traditionally described optical oscillators based on stimulated emission, although phonon lasers and atom/matter lasers are also common.

In some applications, the process of laser photons and phonons at the same time is useful. These include the development of submillimeter acoustic tweezers. Combining ultrasound and photonic bioimaging improves imaging quality and the range of dual-domain lasers across quantum information processing and sensing. Existing demonstrations show that Stokes optical sound waves are a by-product of phonon lasers. In this work, Wang and his colleagues developed a coupled oscillator system that emits lasers from two different physical domains pumped by the same source to show how dual-domain concurrent photon and phonon lasers enhance the output power of photon and phonon lasers.

Figure: Experimental setup. (A) Demonstration of a two-domain synchronous phonon and photon laser based on forward multimode SBS in a 10 m TMF ring cavity. (B) refractive index distribution of reduced cladding TMF used as a gain medium in two-domain (phonon and photon) lasers. (C) Microscope cross-section images of TMF. (D) Measured model profiles of three modes of TMF at λ = 976 nm. Source :Science Advances (2023). DOI: 10.1126/sciadv.adg7841

principle

The team used forward stimulated Brillouin scattering to generate low-frequency curved sound waves; The interaction of photons and phonons in a two-mode fiber. Low-frequency phonons are confined to silicon fibers and have a longer life of 10 milliseconds. With a propagation length of about 10 meters, phonons can also produce laser light. In the experimental setup, the coherent oscillation of the light waves enhances the gain of the phonons, and vice versa, resulting in laser light in both domains.

The team noted that by increasing the optical pump power to generate photon and phonon lasers, the device has four functional states in which the gain of Stokes light and sound waves must outweigh their loss. The experimenters devised a way to allow phonon energy inside the ring cavity to boost the phonon laser. When the phonon laser power is confined to the cavity, the Stokes optical laser can be seen at the output of the coupler.

experiment

In the experiment, the researchers used a 976 nm fiber-coupled pumping diode with a maximum output power of 400 mW. They use thermoelectric coolers to regulate the functional temperature of the system. The pump beam is coupled into a two-mode fiber to form an outer diameter ring cavity.

The scientists used a simplified clad dual-mode fiber made of pure silica cladding and germanium oxide doped silica core. Since the sound field extends to the entire cladding, the process of reducing the cladding size of the dual-mode fiber improves the overlap between the acousto-optical fields, thus increasing the gain coefficient of stimulated Brillouin scattering.

Laser power

The team measured the phonon laser output power as a function of the pump power injected into the ring cavity, resulting in two thresholds corresponding to the photon laser and the phonon laser. The threshold pumping power of the photon laser is 180 mW. When they increased the pumping power to 308 mW, the phonon laser also began to emit laser light.

The measured threshold pump power and output laser power are in agreement with the numerical simulation results. The photon-phonon laser has a retrodissipative hierarchy, and the acoustic emission line width is much narrower than the pumped laser line width compared with the existing standard.

foreground

In this way, the researchers showed how two coherently coupled lasers in different physical domains can perform a variety of practical tasks. Light and sound have different spatiotemporal characteristics and different interactions with materials. Therefore, their availability can be explored differently. This phenomenon of coupling lasers in two different physical domains in the same cavity is the first result of the study. This result goes beyond already established methods, including coherently coupled lasers such as laser diode arrays.

The two-domain laser explores forward multimode stimulated Brillouin scattering and realizes the coupling of photon and phonon synchronous laser in the same cavity. Due to the lack of high-resolution and high frame rate cameras, the team did not directly observe phonon laser power in this study. The scientists observed several laser functions associated with self-released lillouin scattering, photon lasers, and photon-phonon lasers, which are consistent with theoretical models of two-domain lasers. This result will lead to future developments in optical mechanics and will lead to the development of multi-domain lasers and related applications.

Source: Chinese Optical Journal Network