This paper reports on a non-modulated all-fiber LHR setup that utilizes a 1.316 μm narrow-linewidth DFB laser as the local oscillator. This device abandons the traditional method of using a chopper and a lock-in amplifier for modulation and demodulation. Instead, it employs multiple averaging techniques, reducing the complexity of the signal processing module in the LHR. This approach avoids the impact of low-pass filtering during demodulation on the instrument line shape function and measurement speed of the LHR, thereby enhancing spectral resolution and effectively improving the system's measurement speed. In May and June 2024, field measurements were conducted in the Changxing Island area of Dalian. The LHR signals of water vapor molecules in the 7597-7598 cm⁻¹ range were obtained with a spectral resolution of 0.003 cm⁻¹. The processed signals were then wavelength-calibrated and normalized, resulting in the relative transmittance spectrum of the entire atmospheric column for water vapor molecules. An optimal estimation method was used to establish a LHR retrieval algorithm. The retrieval ultimately yielded vertical profiles and column concentrations of water vapor molecules throughout the entire atmosphere. The research findings indicate that the non-modulated all-fiber approach can simplify the structure of the LHR, improve device performance, and has significant implications for the optimization and integration of LHR.
Metal isotope abundance detection is significant in earth science, environmental monitoring and industrial applications. A new technique for the detection of metal isotopes was developed by wavelength modulation spectroscopy technology in this work. The measurements were made for the rubidium transition at 795 nm using four kinds of rubidium compound samples (RbCl, Rb2CO3, Rb2SO4, and RbI). Based on the redox reaction, the solid rubidium compound was mixed with the reducing agent. The micro-channel array structure of the atomic generator can produce highly collimated atomic vapor. The ability of high-order harmonics (2nd, 4th, and 6th) to suppress system noise was compared, and the result showed that the fourth-harmonic signal not only enhanced signal-to-noise ratio but also ensured effective spectral resolution. Compared with direct absorption, the signal-to-noise ratio of the 4th harmonic was enhanced by approximately 3.3 times. In addition, wavelet denoising further suppressed the baseline standard deviation of the system by about a factor of 1.
The increase of greenhouse gas concentration is the most important factor leading to global warming, and the accuracy of carbon dioxide column concentration is required to be better than 0.25% in the total carbon column observation network. As the prior value of inversion model, the influence of prior profile on inversion accuracy needs to be further clarified. Based on Observation of the column-averaged dry air mole fractions of carbon dioxide in Hefei, the sensitivity of temperature profile, pressure profile and CO2 molecular profile to the column-averaged dry air mole fractions retrieval was analyzed. The main results are as follows: The temperature and pressure profiles have significant influence on the inversion results, the relative deviation of retrieving CO2 column concentration from the temperature and pressure profiles of 1976 US standard atmosphere and NCEP is 3.8%, and the maximum absolute deviation between them is 14ppm; The shift of the prior CO2 profile has no effect on the inversion accuracy. However, the change of the profile shape has a significant effect on the inversion accuracy. Therefore, using real-time temperature and pressure profiles and accurate gas prior profiles can improve the retrieval accuracy of greenhouse gas CO2 column concentration. These results provide a theoretical basis for the inversion of greenhouse gas column concentration in China.
Above-low-cloud aerosol (ACA) has important impacts on low clouds bellow. Based on the satellite data from 2007 to 2010, this study analyzed the relationship between ACA optical depth (OD), ACA occurrences and low cloud integrated color ratio (CR) over tropic Atlantic region where ACA frequently occurs. The results show that, the integrated attenuated CR (IACR) of low cloud is about 30%-50% larger over smoke region in smoke outbreak seasons than other regions or seasons. However, the IACR of low cloud over dust region shows small difference between dust outbreak seasons and other seasons. It indicates that above-low-cloud smoke aerosol can introduce stronger color effect than dust. The integrated corrected CR (ICCR) of low cloud tends to decrease with increasing above-cloud dust OD, while the low cloud ICCR shows weak relationship with above-low-cloud smoke OD. And, the above-low-cloud dust aerosol could introduce strong microphysics effect, that is, the low cloud droplet size may decrease with increasing burden of dust aerosol above.
In this paper, a new idea is put forward under the background that static high voltage DC power is commonly used to replace lightning in the femtosecond laser-guided lightning simulation experiment. We use a single chip microcomputer as the controller to generate controllable Pulse Width Modulation(PWM) wave signal,then through PWM control high voltage.So controllable high voltage in the femtosecond laser-guided lightning simulation experiment is formed by the method of weak voltage(namely PWM) controlling high voltage. In the experiment, the period and duty ratio of PWM output by the single-chip microcomputer are indirectly controlled by controlling the internal timer counter A, optocoupler and SCR are used as the safe isolation module between high and weak voltage. The experimental results show that the controllable high voltage in the femtosecond laser-induced high voltage discharge experiment can be easily and effectively obtained by adding a controller to control. At the same time, it can help us to analyze the influence of the different high voltages on the experimental parameters of femtosecond laser guided high voltage discharge.
A ground-based Fourier transform spectrometer has been established in Hefei, China to remotely measure H2O, CO2, CH4 and CO based on near-infrared solar spectra. The continuously retrieved time series of total column results for H2O, CO2, CH4 and CO are presented on April 2nd, 2018. The observation results show the variation of total column of CO2, CH4 and CO. The total columns of H2O, CO2, CH4 and CO are 1.35×10 23, 8.91×1011, 4.08×10 19 and 4.09×10 18 molecules/cm2, respectively. In order to reduce the systematic error of the instrument, we also calculate the column-averaged dry air mole fraction by the oxygen molecule as the internal standard. The column-averaged dry air mole fraction of H2O, CO2, CH4 and CO are 5289.43, 415.04, 1.907 and 0.178ppm, respectively. Furthermore, we analyze the atmospheric transmittance by using MODTRAN 5.0 based on the retrieved results. The comparison results show that the atmospheric transmittance has gaps in the absorption band
Laser ablation absorption spectroscopy (LAAS) is an analytical technique by combining diode laser absorption spectroscopy (DLAS) with laser ablation (LA) technique. It has been developed to atomize various samples and distinguish elements and isotopes directly without chemical separation. This article reviews the principle and recent research highlights of LAAS technique.
The beam spreading, induced by atmospheric turbulence and thermal blooming when a high-energy laser beam propagates through the atmosphere, is numerically calculated and analyzed. The simple scaling relation between the beam quality factor and the characteristic parameters of atmospheric effects is obtained, and can be given by the expression β2u = 1 + 0.636N1.558. Moreover, when the distortion parameter N is less than one, the beam spreading is mostly dependent on the linear effects because of the weak thermal blooming effects. However, with the thermal blooming effects strong gradually, the beam spreading induced by the combined effects of turbulence and thermal blooming increases rapidly.
A new method, named FSI (Fourier Shear Interferometry), is suggested to calculate the phase derivative by Fourier transform of the lateral shear fringes. After filtering intensity spectrum AF2 (fx, fy)in the spectrum of the shear fringes, the cross term of the fringe’s intensity, i.e., A(x,y)A(x + s, y)exp[i▵xφ(x,y)], is obtained by the reverse Fourier transform, and then ▵φ(x, y) can be easily obtained if only |▵φ(x, y)|less than or equal to π. The numerical simulation results demonstrate feasibility and accuracy of the suggested method.
By using the time-dependent propagation computer code, adaptive compensation for thermal blooming effects, which are induced by collimated high-energy laser (HEL) beam propagation through the atmosphere, is numerically calculated and analyzed under different conditions. The numerical results show that, with the definite adaptive optics (AO) system, the scaling parameter NJY'NFB is available to evaluate the effect of adaptive compensation efficiently. Moreover, we get the scaling relation between the scaling parameter ND/NFB and the far-field Strehi ratio, which is can be described by Strehl=1/[1+AND/NFB+B (ND/NFB) C] where A, B and C are fitting parameters. We also get the threshold of adaptive phase compensation instability (PCI) through analysis ofthe scaling relation above. In addition, we discuss the difference between adaptive compensation and whole-beam compensation.
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