Abstract:Cascaded Raman fiber lasers based on random distributed feedback (RDFB) are proven to be wavelength agile, enabling high powers outside rare-earth doped emission windows. In these systems, by simply adjusting the input pump power and wavelength, highpower lasers can be achieved at any wavelength within the transmission window of optical fibers. However, there are two primary limitations associated with these systems, which in turn limits further power scaling and applicability. Firstly, the degree of wavelengt… Show more
“…When an excitation light source of fixed wavelength ( hv I ) is irradiated on a medium, the working medium will generate an optical phonon ( hv q ) and emit a photon with energy hv S ( hv S = hv I – hv q ) at the same time. As the temperature of the test environment changes, effects such as the phonon anharmonic effect, thermal expansion effect, and substrate effect will make the output optical phonon wavelength adjustable continuously with a high quality within a certain range (as shown in Figure b, c). , …”
Integrated optics shows great potential in the current optical communication systems, sensor technology, optical computers, and other fields. Tunable laser technology within a certain range is the key to achieving on-chip optical integration; to realize which, Raman scattering is a competitive method that can effectively transfer incident laser energy to optical phonons due to the photon−phonon interaction. Here, we take hexagonal boron nitride as the energy conversion medium, and based on the angle-resolved polarized Raman spectroscopy, it is found that when laser polarization vector e i ⊥ c axis, the spectrum obtains maximal scattering across the cross section and a minimal depolarization ratio. At room temperature, h-BN obtains an output signal with a wavelength of 522.8 nm and a full-width at half-maximum of 0.24 nm under the excitation of 488 nm pump laser, and the depolarization ratio is 0.09 (theoretically, it is 0, and this difference is due to experimental errors). And then, within the temperature range of 80∼420 K, the scattered light wavelength shows a high-precision shift of 0.006 nm/25 K, indicating that continuous wavelength tuning has been successfully achieved in h-BN.
“…When an excitation light source of fixed wavelength ( hv I ) is irradiated on a medium, the working medium will generate an optical phonon ( hv q ) and emit a photon with energy hv S ( hv S = hv I – hv q ) at the same time. As the temperature of the test environment changes, effects such as the phonon anharmonic effect, thermal expansion effect, and substrate effect will make the output optical phonon wavelength adjustable continuously with a high quality within a certain range (as shown in Figure b, c). , …”
Integrated optics shows great potential in the current optical communication systems, sensor technology, optical computers, and other fields. Tunable laser technology within a certain range is the key to achieving on-chip optical integration; to realize which, Raman scattering is a competitive method that can effectively transfer incident laser energy to optical phonons due to the photon−phonon interaction. Here, we take hexagonal boron nitride as the energy conversion medium, and based on the angle-resolved polarized Raman spectroscopy, it is found that when laser polarization vector e i ⊥ c axis, the spectrum obtains maximal scattering across the cross section and a minimal depolarization ratio. At room temperature, h-BN obtains an output signal with a wavelength of 522.8 nm and a full-width at half-maximum of 0.24 nm under the excitation of 488 nm pump laser, and the depolarization ratio is 0.09 (theoretically, it is 0, and this difference is due to experimental errors). And then, within the temperature range of 80∼420 K, the scattered light wavelength shows a high-precision shift of 0.006 nm/25 K, indicating that continuous wavelength tuning has been successfully achieved in h-BN.
“…Figure 4 shows the variations of the linewidths versus the input pump energy for the first and second stokes signals. A slightly observed broadening in both Raman stokes with increasing the pump energy is attributed to the more intense nonlinear effects such as self phase modulation (SPM) at higher pump energies 4 , 5 , 27 . Figure 4 The linewidth (FWHM) of 1st Stokes (blue squares) and 2nd Raman Stokes (red circles) as a function of the input pump energy.…”
Section: Resultsmentioning
confidence: 99%
“…Colloidal solutions and metamaterials have also been offered for tuning elastic scattering to enhance the Raman signals generation 26 . But, observation of several Stokes orders (cascaded SRS generation) is only reported in systems such as fibers 4 – 7 , 27 – 30 , Raman crystal under high-intensity pump pulses 31 – 34 , and the barium sulfate (BaSO 4 ) powders 18 , in our knowledge.…”
This study reports the first experimental observation of cascaded stimulated Raman scattering (SRS) generation in a colloidal disordered medium. Generation of the cascaded effect requires both a high Raman gain and pump power in the disordered medium. Here, to extend effective path lengths of photons into the Raman gain medium for producing additional SRS processes, ZnO microspheres with abundant nano-protrusions as suitable scattering centers are proposed. It is explained that nano-protrusions on the surface of the spheres can act as nano reflectors and significantly provide potent feedback in the disordered system. This provided feedback via nano-protrusions boosts cascaded SRS generation to allow the appearance of higher Raman signals of Rhodamine 6G dye solution at a low scatterer concentration of 5 mg/ml. The threshold for the formation of the first Raman signal is measured at about 60 mJ/pulse. Also, the evolution of Raman signals under several fixed pump pulses is examined to investigate the stability from pulse to pulse. Our findings provide promising perspectives for achieving the single-frequency laser sources and generate desirable wavelengths for specific applications.
“…3. Previous reports have shown that a temporally stable pump source is of great importance for high-performance RDFLs [36][37][38] ; therefore, a superfluorescent fiber source (SFS) with customizable optical spectrum is used as the Raman pump seed [39] , providing an output power of about 40 W. To extract the backward FBG leakage, a 10/125 μm circulator is spliced after the SFS. Subsequently, a mode field adapter (MFA) with input and output fiber dimensions of 10/125 μm and 20/400 μm, respectively, is then connected after the circulator.…”
High-power operation is one of the most important research topics surrounding random fiber lasers (RDFLs). Here we optimized the cavity structure and proposed a new scheme based on hybrid gain to address the issue of high-power backward light in traditional kilowatt-level RDFLs. Consequently, a record power of 1972 W was achieved while the maximum backward leaked power only reached 0.12 W. The conversion efficiency relative to the laser diode pump power was 68.4%, and the highest spectral purity of the random lasing reached 98.1%. This work may provide a reference for high-power RDFLs, Raman fiber lasers, and long-wavelength Yb-doped fiber lasers.
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