Tunable dual-frequency oscillation is demonstrated in a vertical external-cavity surface-emitting laser. Simultaneous and robust oscillation of the two orthogonally polarized eigenstates is achieved by reducing their overlap in the optical active medium. The class-A dynamics of this laser, free of relaxation oscillations, enables one to suppress the electrical phase noise in excess that is usually observed in the vicinity of the beat note.
Surface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz.
We report on femtosecond operation of a broadband diode-pumped external-cavity surface-emitting semiconductor laser, passively mode locked with a fast quantum–well Semiconductor Saturable Absorber Mirror grown at 735 °C. We obtained 477 fs pulses at 1.21 GHz. The average output power is 100 mW at 1040 nm, the pulse peak power 152 W, with ∼1 W of 830 nm pump. The rf spectrum shows a linewidth <50 kHz at the noise level (−65 dB). We believe that the group-delay dispersion is compensated by the negative self-phase modulation in the absorber structure, leading to soliton-like mode locking. This system requires no additional technological step after the growth of the structures.
We demonstrate high power (2.1W) low noise single frequency operation of a tunable compact verical-external-cavity surface-emitting- laser exhibiting a high beam quality. We took advantage of thermal lens-based stability to develop a short (3-10 mm) plano-plano external cavity without any intracavity filter. The semiconductor structure emitting at 1microm is optically pumped by a 8W commercial 808 nm multimode diode laser at large incidence angle. For heat management purpose the GaAs-based VECSEL membrane was bonded on a SiC substrate. We measured a low divergence quasi-circular TEM00 beam (M2 = 1.2) close to diffraction limit, with a linear light polarization (>30 dB).We simulated the steady state laser beam of this unstable cavity using Fresnel diffraction. The side mode suppression ratio is > 45 dB. The free running laser linewidth is 37 kHz limited by pump induced thermal fluctuations. Thanks to this high-Q external cavity approach, the frequency noise is low and the dynamics is in the relaxation-oscillation-free regime, exhibiting low intensity noise (< 0.1%), with a cutoff frequency approximately 41MHz above which the shot noise level is reached. The key parameters limiting the laser power and coherence are studied. This design/properties can be extended to other wavelengths.
Fourier transform spectroscopy and intracavity laser absorption spectroscopy are used to record the absorption spectrum of formic acid at high spectral resolution, in the ranges of the 2νOH (6968.258 cm−1) and 4νOH (13 284.075 cm−1) vibrational bands of the trans-rotamer, respectively. Numerous perturbations combined with a large line density limit the extent to which the vibration–rotation analysis is performed. Some 689 lines are assigned in the first overtone band and related vibration–rotation constants are determined. Only the band origin and upper state principal A-rotational constant are determined for the n=4 overtone band, because of much higher spectral density. Interpolation, helped by literature data, provides all missing principal rotational constants in the nOH series, for n=1 to 4. All major vibration–rotation parameters appear to evolve very smoothly along the series. This trend is fully supported by ab initio calculations performed at the MP2/cc-pVTZ level of theory and based on an effective one-dimensional model describing the OH local mode stretching vibration. Results of these calculations are detailed in terms of the mean nuclear structure in the excitation series, up to n=4. The related calculated dipole moment surface allows the experimental a:b subband intensity ratio in the series to be interpreted in terms of a decrease in the HOC angle, from Θ≈90° (n=1) to 44°(n=4). The potential occurrence of a proton exchange mechanism between the two oxygen nuclei, close to a tautomerism mechanism, is discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.