Pulsed Light Wave Research Articles

Applications of LiDAR in Agriculture and Future Research Directions

Light detection and ranging (LiDAR) sensors have accrued an ever-increasing presence in the agricultural sector due to their non-destructive mode of capturing data. LiDAR sensors emit pulsed light waves that return to the sensor upon bouncing off surrounding objects. The distances that the pulses travel are calculated by measuring the time for all pulses to return to the source. There are many reported applications of the data obtained from LiDAR in agricultural sectors. LiDAR sensors are widely used to measure agricultural landscaping and topography and the structural characteristics of trees such as leaf area index and canopy volume; they are also used for crop biomass estimation, phenotype characterisation, crop growth, etc. A LiDAR-based system and LiDAR data can also be used to measure spray drift and detect soil properties. It has also been proposed in the literature that crop damage detection and yield prediction can also be obtained with LiDAR data. This review focuses on different LiDAR-based system applications and data obtained from LiDAR in agricultural sectors. Comparisons of aspects of LiDAR data in different agricultural applications are also provided. Furthermore, future research directions based on this emerging technology are also presented in this review.

Resonant effects in the spontaneous bremsstrahlung process of ultrarelativistic electrons in the fields of a nucleus and a pulsed light wave

This article focuses on the resonant high-energy spontaneous bremsstrahlung of ultrarelativistic electrons with considerable energies GeV in the field of a nucleus and a quasimonochromatic laser wave with an intensity ÷ 1017 W cm−2. Under resonant conditions within the light field the intermediate virtual electron transformed into a real particle. Therefore, the initial second order process in accordance with the fine structure constant in the laser field effectively reduced to two successive processes of the first order: the laser-stimulated Compton-effect and laser field-assisted scattering of an electron by a nucleus. In this work we derive the expressions for the resonant differential cross-sections of this processes using the simultaneous registration of the frequency and outgoing angle of the spontaneous photon and the absorption of the rth wave of photons (where r = 1,2,3,...is the resonance number). To summarize, for the first resonance of channel A, the resonant differential cross-section attains a magnitude of the ∼1012 and the third resonance of channel B attains ∼105 in units of . Finally, scientific laser pulse radiation (SLAC, FAIR, XFEL, ELI, XCELS) can be used to verify the model calculations.

Resonant effect of the ultrarelativistic electron–positron pair production by gamma quanta in the field of a nucleus and a pulsed light wave

Resonant electron–positron pair production by a high-energy gamma quantum in the field of a nucleus and a quasi-monochromatic laser wave with the intensities – was theoretically studied. Under the resonant condition, an intermediate virtual electron (positron) in the laser field becomes a real particle. Due to this fact, the initial process of the second order in the fine structure constant of a laser field effectively reduces into the two successive processes of the first order: the laser-stimulated Breit–Wheeler process and the laser-assisted process of an intermediate electron (positron) scattering by a nucleus. It is shown that there is a threshold energy for the initial gamma quantum, which significantly depends on the number of absorbed wave photons. At the resonance, the electron–positron pair energies are determined by the outgoing angle between the momenta of the initial gamma quantum and the positron (for the channel A) or the electron (for the channel B). The differential cross-sections for the first few resonances with simultaneous registration of the energy and the outgoing angle of the positron or the electron were obtained. For the initial gamma quantum energy the resonant electron–positron pair energies for the case of the first three resonances can be measured with a very high magnitude of the differential cross-section: from ∼1013 for the first resonance to ∼108 (in the units of ) for the third resonance.

Brillouin Optical Correlation-Domain Technologies Based on Synthesis of Optical Coherence Function as Fiber Optic Nerve Systems for Structural Health Monitoring

Brillouin optical correlation-domain technologies are reviewed as “fiber optic nerve systems” for the health monitoring of large structures such as buildings, bridges, and aircraft bodies. The Brillouin scattering property is used as a sensing mechanism for strain and/or temperature. Continuous lightwaves are used in the technologies, and their optical coherence properties are synthesized to realize position-selective measurement. This coherence manipulation technology is called the “synthesis of optical coherence function (SOCF)”. By utilizing SOCF technologies, stimulated Brillouin scattering is generated position-selectively along the fiber, which is named “Brillouin optical correlation domain analysis (BOCDA)”. Spontaneous Brillouin scattering, which takes place at any portion along the fiber, can also be measured position-selectively by the SOCF technology. This is called “Brillouin optical correlation domain reflectometry (BOCDR)”. When we use pulsed lightwaves that have the position information, sensing performances, such as the spatial resolution, are inherently restricted due to the Brillouin scattering nature. However, in the correlation-domain technologies, such difficulties can be reduced. Superior performances have been demonstrated as distribution-sensing mechanisms, such as a 1.6-mm high spatial resolution, a fast measurement speed of 5000 points/s, and a 7000-με strain dynamic range, individually. The total performance of the technologies is also discussed in this paper. A significant feature of the technologies is their random accessibility to discrete multiple points that are selected arbitrarily along the fiber, which is not realized by the time domain pulsed-lightwave technologies. Discriminative and distributed strain/temperature measurements have also been realized using both the BOCDA technology and Brillouin dynamic grating (BDG) phenomenon, which are associated with the stimulated Brillouin scattering process. In this paper, the principles, functions, and applications of the SOCF, BOCDA, BOCDR, and BDG-BOCDA systems are reviewed, and their historical aspects are also discussed.

Parametric interference effect in nonresonant pair photoproduction on a nucleus in the field of two pulsed light waves

Nonresonant electron-positron pair photoproduction on a nucleus in the field of two pulsed light waves is studied theoretically. The process is considered in detail within the interference kinematic region, when stimulated absorption and emission of photons of external pulsed waves by an electron and a positron occurs in a correlated manner. Within this region, a correspondence between the emission angle and energy of the produced particles appears. The distribution of the obtained differential cross section over the pair kinetic energy is characterized by presence of oscillations, within the interference region. Each of the maxima corresponds to the definite partial process with emission and absorption of an equal number of photons of both waves. It was shown that the differential cross section within the interference region for certain values of the pair energy may exceed the cross section in other scattering kinematics in two orders of the magnitude. Obtained results may be experimentally verified, for example, by scientific facilities at sources of pulsed laser radiation (SLAC, FAIR, ELI, XCELS).

Resonant Interference Effect in Scattering of an Electron by an Electron in the Field of Two Pulsed Laser Waves

Resonant scattering of an electron by an electron in the field of two unidirectional pulsed laser waves is studied theoretically. The interference kinematical region is considered. Stimulated emission and absorption of external waves' photons by electrons is correlated in the interference region. Resonance condition in the interference region is specified. Analytical expressions for the amplitude and differential cross section of the process for waves' circular polarization are obtained in the first order of the perturbation theory. The cross section contains resonant peaks, their altitude and width are determined by external waves parameters. Considerable effect of wave polarization on the character of stimulated emission and absorption of external waves' photons is found. It is demonstrated that the differential interference cross section of scattering of nonrelativistic electrons by each other in the field of two pulsed light waves of the optical frequency is approximately ten times greater in the magnitude than the corresponding one in the external field absence. Obtained results can be verified experimentally, for example, at the SLAC National Accelerator Laboratory (Stanford, USA) or in the frame of the FAIR Project (Darmstadt, Germany).

Nonresonant Compton scattering in an intense pulsed laser field

The influence of an intense pulsed light wave on nonresonant scattering of a photon by an electron is investigated in the approximation when the pulse width is considerably greater than the characteristic time of wave oscillation. The partial differential cross-sections for different numbers of absorption (emission) wave photons are analyzed for a range of external field intensities I ∼ 1017 W cm−2. The general relativistic expression for the nonresonant cross-section of laser-modified Compton scattering summed over all possible partial processes is derived. It is shown that for nonrelativistic energies the pulse character of the external field significantly affects the process.

Influence of an intense pulsed electromagnetic field on nonresonant scattering of a photon by an electron for the nonrelativistic energy

The theory of nonresonant scattering of a photon by an electron in the field of an intense pulsed light wave is developed. The approximation when a pulse width is considerably greater than the characteristic time of wave oscillation is considered. The nonresonant kinematic region is determined. The general relativistic expression for the nonresonant cross-section is derived for the range of the external field intensities if η 0 ≲ 1, η0 2 ≪ 1 (see Eq. (12)) is valid. The obtained differential cross-section of the process has form of a sum over partial differential cross-sections. Each of them corresponds to the process with emission (absorption) of a certain number of wave photons. It is shown, that for nonrelativistic energy the cross-section summed over all possible partial processes differs considerably from the cross-section of Compton scattering if the external field is absent and may exceed the latter over than 200%.

Nonresonant photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave

The nonresonant Coulomb photocreation of electron-positron pair on a nucleus in the field of a pulsed light wave is theoretically investigated. The approximation is examined when pulsewidth is considerably greater than the characteristic time of wave oscillations. The interaction of an electron and a positron with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation). An analytic expression for the nonresonant differential cross section was obtained for the range of moderately strong fields in the case relativistic and nonrelativistic energies. It is shown, that the nonresonant cross section of Coulomb photocreation of nonrelativistic pair in the field of a pulsed light wave is two times larger than the cross section of Coulomb photocreation in the absence of an external field.

Resonant electron-positron pair photoproduction on a nucleus in a pulsed light field

The resonant photoproduction of an electron-positron pair on a nucleus in the field of a pulsed light wave is studied theoretically. The approximation where the electromagnetic pulse duration is much longer than the characteristic time of wave oscillations is considered. The interaction of the electron and positron with the Coulomb potential of the nucleus is considered in the Born approximation. An analytical expression for the resonant differential cross section is derived for the range of moderately strong external fields. This cross section contains a resonant peak whose height and width are determined by the external pulsed wave characteristics. The resonant cross section for pair photoproduction on a nucleus in a pulsed laser field can exceed the corresponding cross section for pair photoproduction on a nucleus in the absence of an external field by an order of magnitude.

Resonant scattering of a lepton by a lepton in the pulsed light field

The process of resonant scattering of a lepton by a lepton in the field of pulsed light wave in general relativistic case is studied theoretically. The approximation when a pulsewidth is considerably greater than the characteristic time of wave oscillation is considered. The analytical expression for the resonant differential cross-section of concerned process is derived within the framework of the first order of the perturbation theory with respect to external laser field; it contains the resonant peak, the altitude and the width of which are defined by the external pulsed wave characteristics. It is demonstrated, that the resonant differential cross-section of scattering of an electron by an electron (an electron by a positron, an electron by a muon) in the pulsed light field may be several orders of magnitude greater than the corresponding one in the external field absence. The derived results may be verified experimentally for example by scientific facility at SLAC National Accelerator Laboratory.

Resonant spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of a pulsed light wave

Resonant spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of a pulsed light wave is theoretically investigated. The approximation is examined when the pulse width is considerably greater than the characteristic time of wave oscillations. The electron interaction with the Coulomb potential of a nucleus is considered in the Born approximation. An analytic expression for the resonant differential cross section of the investigated process was obtained for the range of moderately strong fields. The bremsstrahlung cross section contains a resonant peak. The resonant peak's altitude and width are defined by the external pulsed wave properties. The resonant cross section is studied within the ranges of nonrelativistic, relativistic, and ultrarelativistic electron energies. It is demonstrated that the resonant cross section of spontaneous bremsstrahlung may be several orders of magnitude greater than the corresponding cross section in the absence of an external field. Results obtained may be experimentally verified, for example, by the scientific facilities at the SLAC National Accelerator Laboratory.

Nonresonant spontaneous bremsstrahlung by a relativistic electron scattered by a nucleus in the field of pulsed light wave

This paper presents theoretical study of nonresonant spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of the pulsed light wave. The electron interaction with a Coulomb potential of a nucleus is considered in the first order of perturbation theory (the Born approximation), and the interaction with an external pulsed field is taken into account accurately. The approximation is examined when pulsewidth is considerably greater than the characteristic time of wave oscillations. The obtained differential cross-section of the process has form of a sum over partial differential cross-sections. Each of them corresponds to processes with emission (absorption) of certain number of wave photons. It is shown, that for spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of a pulsed light wave the distribution of a stimulated emission-absorption probability is determined by the average value of corresponding probabilities in the case monochromatic wave.

Reduction of Power Fluctuation in Pulsed Lightwave Frequency Sweepers With SOA Following EDFA

A pulsed lightwave frequency sweeper is a frequency source with linear frequency scanning. It can be made using a fiber ring with an acoustooptic frequency shifter and an optical amplifier. The drawback of this sweeper, however, is optical power fluctuation that is attributable to power feedback to the erbium-doped fiber amplifier (EDFA) by the fiber ring. This study presents suppression of the fluctuation by tandem configuration of optical amplifiers, such as EDFA and semiconductor optical amplifiers in this order, in the fiber ring. The configuration was demonstrated experimentally and its noise performance was evaluated by changing the operation point of the amplifiers

Influence of optical filters on pulse circulation in fiber rings with a frequency shifter and EDFA

Optical fiber ring circuits constructed with frequency shifters and EDFAs are applicable to pulsed lightwave frequency sweepers, wavelength converters, and optical packet buffers. The salient criterion for those applications is how many times the optical pulse can circle the ring. Optical band-pass filters in the ring can serve an important role for pulse circulation because the filter determines the gain bandwidth at every circulation under the condition of signal wavelength shift. This paper clarifies the effects of optical filter response on pulse circulation in the ring through numerical simulation of the EDFA dynamic model, considering the gain spectrum.

Application of synthesizedcoherence function to distributed optical sensing

We have proposed and developed a technique to synthesize an opticalcoherence function into arbitrary shapes. By using thistechnique, which we call the `synthesis of an optical coherence function', variousdistributed optical sensing schemes have been developed, whichhave no mechanical moving parts nor data calculation. In theseschemes, we do not use a pulsed lightwave but instead use acontinuous wave, whose correlation is controlled by frequency modulation or phase modulation. We have proposed a reflectometry system to diagnosefibre optic subscriber networks. Fibre optic distributed forcesensing systems have also been developed, which are applicableto smart structures and security systems. In asimilar way, we have proposed a system to measure straindistribution along an optical fibre through the Brillouinscattering caused in the fibre. Spatial resolution of just 1 cmhas been demonstrated by this system, which is 100 times higherthan the practical limitation of conventional pulsed-lightwavetechniques. Such a high spatial resolution is suitable forsmart material applications. Two- or three-dimensionaldistributed sensing has also been developed by this technique. An optical tomography system has been proposed, which has fewermechanical moving parts. A system for surface shape measurementfor a multi-layered object has also been developed.

Stabilization of pulsed lightwave circulating around an amplified fiber-optic ring incorporating a Lyot depolarizer

We describe an effective method for stabilizing a pulsed lightwave circulating around an amplified fiber-optic ring containing an acoustooptic frequency shifter. By installing a Lyot depolarizer with a large birefringence in the ring, we can effectively suppress the change in the maximum number of the pulse circulations caused by a fluctuation in the ring birefringence. We experimentally confirmed that the change in the number of circulations was suppressed to less than 30, which is very small compared with the maximum number of pulse circulations of 730.

Broad-band absolute frequency synthesis of pulsed coherent lightwaves by use of a phase-modulation amplified optical ring

Broad-band absolute frequency synthesis of over 1.4 THz with a 10-GHz spacing is demonstrated for pulsed lightwaves. It is based on the recirculation of a rectangular pulse around an amplified fiber-optic ring containing a phase modulator, an acoustooptic (AO) frequency shifter, and a high-finesse Fabry-Perot etalon (FPE). The modulation frequency F/sub M/ and the AO frequency shift F/sub AO/ are designed so that F/sub M//spl plusmn/F/sub A/O is the same as the peak interval of the FPE. If one of the peak frequencies is tuned to the frequency of the initial pulse from a master laser, the frequency of the recirculating pulse jumps to the next peak for each round trip while the unwanted frequency components are eliminated by the FPE. We confirmed 70 circulations both for plus and minus frequency shift directions and a covering span was 1.4 THz (140/spl times/10 GHz).

Absolute frequency synthesis of pulsed coherent light waves through phase-modulation active optical feedback

A novel method for the broadband absolute frequency synthesis of pulsed coherent lightwaves is demonstrated. It is based on pulse recirculation around an active optical feedback ring containing a delay-line fiber, an external phase modulator, an acousto-optic frequency shifter (AOFS), and a high-finesse Fabry-Perot étalon. The modulation frequency F(M) and the frequency shift F(AO) that are due to AOFS are designed so that their sum or difference equals the free-spectral range of the étalon and F(AO) is set at larger than the half-width at full maximum of its resonant peaks. If one of the peak frequencies is tuned to the frequency of the initial pulse, the frequency of the recirculating pulse jumps to the next peak for each round trip. In the experiment the absolute frequency is synthesized over a frequency span of 700 GHz around the initial stabilized frequency of the master laser.

Time shared lightwave reference frequency distribution for photonics networks

Time shared lightwave reference frequency distribution is demonstrated using a pulsed lightwave sweep frequency generator, tracking generators, and a linear repeater. The reference lightwave, which contains over 1000 frequencies in 250 MHz steps, is generated using a dynamically gain controlled erbium-doped fiber amplifier and acoust-optical deflector. Continuous lightwave frequencies locked to the distributed time shared reference frequency are generated over a 200 GHz range with an instability of only /spl plusmn/5 MHz. Absolute lightwave frequency from the tracking generator is confirmed by a frequency chain between two hydrogen cyanide gas cell stabilized lightwave sources. The effect of fiber nonlinearity encountered in frequency distribution, a dynamically gain stabilized linear repeater, and system design are also discussed.