The effect of the relative phase on the spectral linewidth of electromagnetically induced transparency is studied in a
Λ-type three-level configuration coupled by double coupling fields and the result is presented in this paper. We show that
the relative phase between the double coupling fields has a great degree of influence on the spectral width of
electromagnetically induced transparency window. The linewidth can be controlled by changing the relative phase.
Particularly, as the double coupling fields have opposite phases, the linewidth of EIT window can be extremely narrow
distinctly.
KEYWORDS: Carbon monoxide, Absorption, Signal detection, Tunable diode lasers, Absorption spectroscopy, Modulation, Signal processing, Gas lasers, Data processing, Laser systems engineering
Tunable diode laser absorption spectroscopy (TDLAS) is a method to detect trace-gas qualitatively or quantitatively
based on the tunable characteristic of the diode laser to obtain the absorption spectroscopy in the characteristic
absorption region. The concentration of CO is measured by tunable diode laser absorption spectroscopy (TDLAS)
technology in this paper. The experimental results of measurement signals are inversely processed by applying the
overall second harmonic least squares data processing algorithm. The experimental results indicate that the signal
strength of the second harmonic spectrum changes with CO concentration. But the widths of the 2f lineshapes have not
changed. The components that influence the uncertainty of measurement results during measuring CO concentration by
TDLAS are analyzed and the mathematic model is built. The standard uncertainty of components and evaluation of
uncertainty of measurement results are given with the direct evaluation method in detail. The evaluation results indicate
that the major factors affecting measurement uncertainty are the indicating value uncertainty of the apparatus,
concentration definite value uncertainty of calibrating gas.
The Electromagnetically Induced Transparency (EIT) is associated with a Λ three-level system and the spectral
position of EIT window can be changed by varying the frequency of the coupling field, however, at large detuning the
EIT will evolve into a dispersion-like feature and transparency property of EIT become less obvious. In this paper, it is
shown that we can perform EIT frequency tuning by a radio-frequency (rf) field. In the cascade quasic-Λ four-level
system, the absorption profile of probe field is calculated by solving the equations of motion of the density matrix. It is
shown that the Autler-Townes doublet originates from the rf-field induced dynamic Stark effect and the spectral position
of EIT window is determined by the frequency detuning of the coupling field. When the frequency detuning of the
coupling field is half of the rf Rabi frequency, the EIT feature remain its absorptive profile. The frequency tuning rang of
EIT is determined by the rf Rabi frequency, and can be explained using a dressed-state analysis. Therefore, frequency
tuning range of EIT can be controlled by the rf Rabi frequency.
We investigate the quantum interference effects in a cyclic three-level system with a microwave field driving transition between two low levels. By solving the relative density matrix equations of motion, we obtain the absorption profile of the probe field and identify the conditions under which gain may develop. We demonstrate numerically that the absorption line shape depends on the ratio of the intensities of coupling and driving microwave field. When the intensity of coupling field is much weaker than that of driving field, there is a multi-EITs in the probe absorption spectrum. However, if the intensity of both fields is strong, amplification without inversion occurs in different regime of probe frequency. In addition, we predict that larger amplification is obtained when the coupling field is detuned from exact resonance.
An experimental system for liquid concentration measurement was set up based on the optoacoustic effect and a fiber Bragg grating (FBG) underwater sound sensor. Measurement theory and each element of the experimental setup are introduced. The light beam was injected into the liquid by a fiber bundle with a graded-refractive-index lens at the end. A matched FBG was used to demodulate the wavelength shift signals from the sensing FBG. Preliminary experimental results of sodium carbonate liquid concentration measurement were obtained, which verifies the feasibility of the method.
The resonance enhanced multiphoton ionization (REMPI) spectrum of SO2 in the region of 420~540nm is obtained with a picosecond Nd:YAG laser pumped an Optical Parameter Generator and Optical Parameter Amplifier as radiation source. The ionization pathway is analyzed. SO2 molecule is ionized though (4+1) or (4+2) process and via 4p, 5p and 6p Rydberg resonant states. The near quintic variation of the ionization signal versus laser intensity verified this conclusion further. So the spectral lines can be assigned to np Rydberg series. The adiabatic ionization potential and the quantum defect of SO2 are obtained based on the experimental datum, which is 99586 cm-1 and 1.85 respectively.
A survey of the Rydberg states of NO2 accessed in optical-optical two-color double-resonant (OODR) manner by the technique of multi-photon ionization (MPI) spectroscopy is presented. The pump laser is the double-frequency output of a Nd:YAG laser. While the probe laser is an optical parameter generator and optical parameter amplifier (OPG/OPA) pumped by the triple-frequency output 355nm of the former. The OODR-MPI spectrum of NO2 is obtained by scanning the probe laser in the range of 465-535nm under the condition that the pump laser is unfocused and the probe laser is focused on the center of the pump laser beam. The ionization peaks could be attributed to E2∑u←A2B2←X2A1(1+2) resonant transitions. This means that NO2 molecule is excited to the appropriate level of the first excited A2B2 state by absorbing one pump laser (ω1) photon. Then from the first excited state it should take three probe photons (ω2) and via final resonant E2∑u state for the ionization. The bending vibration frequency of NO2 E2∑u state obtained from above ionization spectrum is (608.6±2.2)cm-1. It is consistent with the literature.
The width of an electromagnetically induced transparency (EIT) resonance is studied theoretically for an ideal three-level system in a L-type configuration. The optical Bloch equations are solved and the power broadening behavior of the EIT resonance is studied as a function of both couple and probe laser intensities over a broad range. It is shown that at relative low couple laser intensity there is a quadratic dependence of the EIT width on the couple laser Rabi frequency and at large couple laser intensity the EIT resonance evolve into the well known dynamic Stark splitting and its width has a linear dependence on the couple Rabi frequency. The dependence of the EIT width on the probe laser intensity shows different characteristics with the dependence on the couple laser intensity. Furthermore, the probe laser causes saturation and this is also discussed in this paper.
In this paper we present a theoretical study of the effect of a microwave field on an EIT feature. The EIT feature is associated with the well-known three-level Λ type configuration where a pump and probe laser field couples two separate optical transitions. In addition to these two laser fields, there is a microwave field which drives one of the two lower levels of the Λ type three-level system to another hyperfine level. The EIT feature is studied as a function of microwave field frequency and intensity. Our results show that the presence of a microwave field can dramatically modify the EIT feature. When microwave is resonant with the hyperfine transition, the EIT feature can be split into two EIT features. When it is off resonant with the hyperfine transition, it causes a frequency shift of the EIT feature, reminiscent of the well-known light shift effect.
The resonance-enhanced multiphoton ionization (REMPI) spectrum of NO has been obtained in the range of 420-480nm with a Nd.YAG pumped optical parametric generator and amplifier. The spectral lines can be attributed to NO X2?(v'' = 0,1) ? A2?(v ' = 0,1) and X2?(v'"= 0) ?* E2?(v ' = 0~4)transitions. In this wavelength range, NO molecules are ionized via the resonant intermediate states A2?+ or E2? and by (2+2) or (3+1) REMPI process. The dependence of ion signals on laser intensity is in good agreement with these results.
KEYWORDS: Luminescence, Laser induced fluorescence, Molecules, High power lasers, Oscilloscopes, Physics, Quartz, Signal detection, Signal to noise ratio, NOx
Two-photon laser-induced fluorescence spectrum(TP-LIF) of NO is obtained by using high power laser as excitation source. A few stronger band can be attributed to A2??X2 ? transition. Some molecule constants about NO which in the ground state are deduced by the spectrum. The nature radiation lifetime of NO which is in the excited state A2? is about 180ns by fitting the curve oflifetime verse pressure.
Crystalline carbon nitride thin films are synthesized by pulsed XeCl excimer laser deposition technique following by a high temperature annealing or accompanying a pulsed glow discharge plasma assistance. The composition, the structure and the binding state of the deposited films are analyzed by several techniques such as Scanning electron microscopy, Energy-disperse X-ray (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Experiment results show that the crystalline carbon nitride films preferentially formed at high temperature companying with the nitrogen content reduction and the films graphitization, combining high substrate temperature and nitrogen activation through pulsed discharge is favorable for the formation of (alpha) -C3N4 crystallites.
Silver halide emulsion is an important component of image materials. It can develop permanent image through the absorption of light. It is widely used in many kinds of fields and has a very prosperous prospect. Now many scientists study the properties of image material, but they mainly focus on experimental methods. Computer simulation method opens up a brand-new way in the study of optoelectronic behavior in image materials. Compared with traditional experimental ways, this method is more economical and convenient and has a shorter research period. So it is a very practical method to exploit new type of image materials and perfect photosensitive theory. In this paper, Nucleation & Growth model and Monte Carlo method were adopted to simulate the optoelectronic behavior in image materials and results with different input parameters will be given.
Silver halide emulsion is an important component of image materials. They are widely used in many kinds of fields and have a very prosperous prospect. This kind of method provides a new way to research the photosensitive process of image materials. Compared with the traditional methods, it is more economical and has a shorter experimental period. In this paper, Nucleation and Growth model and Monte Carlo method were adopted to simulate the formation of image and results in different kinds of outside conditions and material properties will be given.
In this paper, the optical emission spectroscopy (OES) is used to study the plasma plume dynamics during XeCl laser ablation of carbon in nitrogen atmosphere. The optical emission spectrum of the plasma is mainly continuous emission near the target in its early formation stage. The discrete spectra can be detected 20ns later and reach the maximum at about 60-100ns. The temporal and spatial evolution of such characteristic peaks as C, C+ and C2 emission lines exhibit different features. The OES results show that the plasma processing dynamics during excimer laser ablated carbon target is :the plasma is produced during the carbon absorbing the laser energy, the particles in the plasma continue their collision process after the laser pulse being over, which make the plasma ionized efficiently, and then the plasma continue expanding, declining and quenching. The creation and evolution mechanism of the active species is also discussed.
In this paper Plasma diagnostics are performed during dc glow discharge plasma-enhanced chemical vapor deposition of carbon nitride thin films using optical emission spectroscopy. The influence of the experimental parameters such as percentage of H2, discharge current and total gas pressure on the emission intensities of the excited species in the plasma is investigated. Based on these results, the excitation mechanism of these species is discussed to gain understanding of the influence of the experiment parameters on the deposition process.
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