Applied Physics B最新文献

We report the development of an optical feedback linear cavity-enhanced absorption spectroscopy instrument for HO₂ detection using a distributed feedback (DFB) diode laser operating at 1506 nm. A direct and accurate method of reflectivity measurement based on the analysis of cavity mode signals was proposed. A differential circuit was used to judge the zero crossing point of the optical feedback cavity mode in the center of the frequency locking region, and shift the laser operating current to the non-resonant region. In this way, a ring-down signal was obtained with a time of 17.9 μs, corresponding to an effective absorption pathlength of 5.37 km. Combining the standing wave condition, the relationship between cavity length and drive voltage of the PZT mounted on the cavity rear mirror is translated into a correlation between the transmitted light wavenumber and the PZT voltage. The spectral resolution was improved from 290 MHz to 97 MHz by precisely tuning the PZT voltage. The achieved detection sensitivity of the system was 7 × 10^− 10 cm^− 1 with a data acquisition time of 10.6 s. The absorption spectrum of HO₂ at 6638.205 cm^− 1 was measured at a cell pressure of 50 mbar with a detection limit of 3.24 × 10⁹ molecule/cm³.

We demonstrate a substantial enhancement of gas Raman scattering using a bidirectional multi-pass cavity CERS system, which incorporates a polarization beam-splitting optical path. The system design allows the laser light to traverse the multi-pass cavity for four specific trips, satisfying the need for quick detection of various gas components. Our gas detection experiments using multi-pass cavities with different times of reflection indicate that the addition of polarization beam-splitting optical path gives 1.5 to 1.68 times enhancement of Raman signal compared with that of the system without polarization beam-splitting. For the detection of CH₄, a limit of detection of 1.66 ppm was achieved with our system using a multi-pass cell with 41 times of reflection and an integration time of 30s. Our proposed design, which integrates a bidirectional multi-pass cavity with polarization beam-splitting optical path, gives an economical multicomponent gas detection system and a valuable tool for guiding the design and precise alignment of these cavities. This system shows significant promise for applications in e.g. human breath and environmental monitoring.

The space-borne Integrated Path Differential Absorption (IPDA) lidar can measure the global distribution of CO₂. Here, we simulate measurements on the R16 absorption line employing a 1572 nm electro-optic dual-comb interferometer. We introduce a comprehensive modeling and retrieval framework to assess the lidar’s capability in measuring the column-averaged of CO₂ in the atmosphere. The assessment combines data simulation with linearization error analysis to solve the nonlinearity in retrieval. Our findings suggest that positioning any sampling wavelength at the absorption peak will significantly increase the random error by about 30%. The lidar can operate with an optimal wavelength strategy where the wavelength bias has virtually no effect, but it must still account for the effects of atmospheric temperature and pressure. We performed a comprehensive global evaluation using geophysical data, comparing results across 3 to 17 wavelengths. Distributing 20 W launched power over 11 wavelengths enables measurement with an error below 0.9 ppm over most of the Earth’s surface.

We propose a new scheme for the study of three-dimensional (3D) atom localization by observing spatially modulated absorption of a weak probe field operating in a multi-wave-mixing induced four-level atomic system. The field-coupled atomic model can be envisaged as a closed-loop double-lambda configuration. By controlling Rabi frequency, detuning, and field-induced collective phase-coherence, different spatial structures of localization patterns are presented with a variety of standing wave field configurations. Our results highlight that 100% detection probability of atom is possible in the present model in many ways with high-precision measurement of spatial absorption. It has been shown that position information of the atom with maximum detection probability can be efficiently controlled by employing a travelling-wave field in association with the standing wave fields in the system. For a specific field configuration, the maximum detection probability of finding the atom can be obtained with a limit of spatial resolution better than (lambda)/40 in our model. The efficacy of the present model is to find its applications in quantum information processing in the near future.

In this work we compute the resonant wavelengths of whispering gallery modes for bulk-fused silica microspheres taking into consideration the material chromatic dispersion. This is done by following two approaches: solving the exact characteristic equation and solving the nonlinear equations that result from the asymptotic approximations for a wavelength-dependent refractive index. Similar results with both methods are obtained with differences below 1%. Nevertheless, important differences are found between the resonant wavelengths computed for a non-dispersive and a dispersive material. We compute the free spectral range and the quality factor, and make a comparison between the variable index and the constant index cases. Our results show that the quality factor is unaffected by chromatic dispersion. However, there are differences of significant relevance in the case of the free spectral range. Our work could be useful as a pathway for designing microspheres for different applications.

In diffusion-cooled gas lasers, the laser medium gas is cooled through the discharge tube wall. Empirical findings suggest that, in longitudinally excited CO₂ lasers with fast pulsed discharges, the materials of the discharge tube and coolant impact the discharge. This study investigates their effects on fast discharges rather than on cooling. Within a discharge tube with a cooling tube, the discharge tube and coolant create a capacitor, influencing the discharge. The laser output energy varies based on the discharge tube and coolant materials. The primary discharge input energy is influenced by these materials, as is the efficiency of converting it into laser output energy.

Nonlinear (NL) absorption and refraction are crucial optical phenomena in the development and application of optical materials. The Z-scan technique, first proposed by Bahae, is widely used to accurately measure the coefficients of NL absorption and refraction. This review presents a comprehensive overview of the most established versions of the Z-scan technique, including the transmittance closed aperture (CA) and open aperture (OA) Z-scan, reflecting CA and OA Z-scan, eclipsing Z-scan, and white light Z-scan. In each version, different sources with varying spatial and temporal intensity distributions are usually utilized. Numerical and analytical calculation results are provided for each version considering both continuous wave (CW) and pulsed laser sources. Unlike conventional reviews, which often summarize previously published results, this review primarily focuses on reproducing the findings from the literature. The analytical results, which are typically derived under specific approximations, are compared with numerical calculations to highlight the limitations of analytically derived relations. Furthermore, the necessary criteria and conditions for applying each Z-scan version are discussed.

Lithium niobate exhibits slow refractive index drift after temperature excursions typical in device manufacturing. Such drift can degrade performance in certain devices. We analyze the birefringence changes in a range of temperatures to measure the magnitude and rate of change. Experiments were conducted by first annealing congruently grown, magnesium doped, and lithium-enriched crystals at a temperatures between 95 and 215 (^circ)C. Subsequent optical evaluation was performed between 95 and 122 (^circ)C using a table-top apparatus. The sample was illuminated with incandescent polarized light and transmitted light was collected with a compact spectrometer after passing through an analyzer so fringes could be recorded. Careful fringe analysis allows a precise estimate of birefringence changes at a reference wavelength with precision (<10^{-6}). The observed birefringence changes can be explained by assuming that existing lithium vacancies re-arrange around positively charged point defects via lithium vacancy migration. Computer simulations for a simple model reproduce the major observations such as magnitude of change, activation energy for relaxation and the stretched exponential nature of the change. Similar effects are expected in lithium tantalate and the results suggest ways to minimize the influence on device operation.

Enhancing the performance of saturable absorbers (SAs) crafted from two-dimensional (2D) narrow-bandgap materials is crucial for their use in ~ 2.0 µm pulse laser applications. In this context, a high-quality TaSe₂ SA was successfully fabricated by mechanical exfoliation. The TaSe₂ SA exhibited saturable absorption characteristics at around 2.0 μm, with a modulation depth of 7.1% and an unsaturated loss of 3.1%. Utilizing this newly fabricated SA, a passively Q-switched Tm:YAP laser operating near 2.0 μm was achieved. At the highest absorbed pump power of 5.58 W, the laser produced a maximum average output power of 1.34 W, with a pulse width measuring 550 ns at 89 kHz. This performance translates to a peak single pulse energy of 15.0 μJ and a maximum peak power of 27.27 W.