Input Laser Pulse Research Articles

Novel transient-state analysis approach for distributed temperature sensing based on spontaneous Raman scattering

The light scattering phenomenon in optical fibres has been implemented in several applications for years. Nowadays, commercial distributed sensing systems for temperature measurements – distributed temperature sensing (DTS) – are gaining more attention and are being applied in many fields. The DTS systems are commonly based on optical time domain reflectometry or optical frequency domain reflectometry analysis approaches. This paper presents the simulation model and primary experimental results of a novel approach for data analysis for DTS systems based on the measurement of the backscattered Raman anti-Stokes radiation: the optical transient-state domain reflectometry. The novelty of this approach is the fast and accurate proposed analysis algorithm, as well as the cost-effective, secure and reliable set-up, whose main aspect is the implementation of long, low-power input laser pulses.

Calculation of the input laser pulse radius's impact on stimulated Raman scattering under self-focusing conditions

Calculation of the input laser pulse radius's impact on stimulated Raman scattering under self-focusing conditions

Photon-phonon quantum cloning in optomechanical system

Quantum cloning is an essential operation in quantum information and quantum computing. Similar to the ‘copy’ operation in classical computing, the cloning of flying bits for further processing from the solid-state quantum bits in storage is an operation frequently used in quantum information processing. Here we propose a high-fidelity and controllable quantum cloning scheme between solid bits and flying bits. In order to overcome the obstacles from the no-cloning theorem and the weak phonon-photon interaction, we introduce a hybrid optomechanical system that performs both the probabilistic cloning and deterministic cloning closed to the theoretical optimal limit with the help of designed driving pulse in the presence of dissipation. In addition, our scheme allows a highly tunable switching between two cloning methods, namely the probabilistic and deterministic cloning, by simply changing the input laser pulse. This provides a promising platform for experimental executability.

Dynamics of spatially confined ns laser induced atmospheric air plasma and shock waves: visualization vis-à-vis validation

A clear visualization of the physical processes of spatially confined ns laser induced atmospheric air plasma within a rectangular glass cavity using optical imaging is presented. The occurrence of various processes starting from the early plasma and shock wave expansion dynamics to shock reflection at the cavity boundaries and compression of the plasma due to reflected shockwaves is studied using defocused shadowgraphy and self-emission imaging techniques. Experimentally, we evidenced that the counter propagating reflected primary shockwaves interact with the expanding plasma generating a secondary shockwave which compresses the plasma core, modifying the plasma morphology resulting in enhanced plasma parameters. The numerical simulations performed via the two-dimensional hydrodynamic (2D-HD) FLASH codes, revealed that the number density increases up to a maximum of 3.6 times compared to the unconfined plasma. The input laser pulse energy and the aspect ratio of the cavity is observed to play a dominant role in the confinement and compression of the plasma.

Neural network-based control of an ultrafast laser

With the recent advances in machine learning (ML) and data science (DS), the control, modeling, and analysis of these complex systems continues to improve. In this work, we report on the optimization of the intensity of a femtosecond laser using feedforward neural networks (FFNN) that model the input–output relationships of the data. The input parameters of the system were optimized to achieve the required performance of the femtosecond laser. We propose a neural network-based control system to model the relationship between the spectral amplitude and phase of the input laser pulse at the amplifier input and the shape of the output pulse. Low-jitter laser parameter inputs and the resulting laser pulse duration were modeled, and the resulting correlation between the input and output data was used to optimize the laser pulse. We demonstrate improved processing and laser control performance.

A quantum information processing machine for computing by observables

A quantum machine that accepts an input and processes it in parallel is described. The logic variables of the machine are not wavefunctions (qubits) but observables (i.e.,operators) and its operation is described in the Heisenberg picture. The active core is a solid-state assembly of small nanosized colloidal quantum dots (QDs) or dimers of dots. The size dispersion of the QDs that causes fluctuations in their discrete electronic energies is a limiting factor. The input to the machine is provided by a train of very brief laser pulses, at least four in number. The coherent band width of each ultrashort pulse needs to span at least several and preferably all the single electron excited states of the dots. The spectrum of the QD assembly is measured as a function of the time delays between the input laser pulses. The dependence of the spectrum on the time delays can be Fourier transformed to a frequency spectrum. This spectrum of a finite range in time is made up of discrete pixels. These are the visible, raw, basic logic variables. Thespectrum is analyzed to determine a possibly smaller number of principal components. ALie-algebraic point of view is used to explore the use of the machine to emulate the dynamics of other quantum systems. An explicit example demonstrates the considerable quantum advantage of our scheme.

Acoustic shock waves emitted from two interacting laser generated plasmas in air.

We present an acoustic detection technique to study the interaction of two shock waves emitted by two nearby, simultaneous, laser-induced air-breakdown events that resembles the phenomenon of interaction of fluids. A microphone is employed to detect the acoustic shock wave (ASW) from the interaction zone. The experiments were done at various separation distances between the two plasma sources. The incident laser energy of the sources is varied from 25 to 100 mJ in ratios from 1:1 to 1:4. The peak sound pressure of the ASW was compared between the single and dual plasma sources, showing that the pressures are higher for the dual plasma source than that of the single plasma. The evolution of peak sound pressures is observed to depend on (a) the pulse energy of the sources and (b) the plasma separation distance, d. For the equal energy sources, the peak sound pressures increased linearly up to a certain plasma separation distance d, beyond which the pressures saturated and decayed. For the case of unequal energy sources, the peak sound pressures showed an interesting response of increase, saturation, decay, and further increase with plasma separation distance d. These observations indicate the dynamics of acoustic wave interactions across the interaction zone of the two sources depend on the input laser pulse energy as well as the plasma separation distance d.

Gain characteristics of stimulated Brillouin scattering in fused silica.

Stimulated Brillouin scattering (SBS) is a non-linear process which has the capacity to improve the beam quality and pulse characteristics of laser beams. In this paper, we theoretically and experimentally study the process of SBS in fused silica. In particular, we examine the energy reflection and pulse compression of input laser pulses as functions of focus position, pump energy and beam diameter. We utilized coupled wave equations and a distributed noise model to simulate the reflected energy and time waveform under different gain parameters. An experimental system is constructed and used to qualify the numerical simulations. The results reveal that the threshold for the SBS process and the energy reflectivity significantly change with laser focus position under the same pump and focusing parameters. Ultimately, the gain characteristics of the SBS material is the primary factor that influences the SBS output. This work presented here offers insight into the operation of short-length solid-state SBS lasers and serves as a basis for the design and optimization of such systems.

Influence of nitro group on solvatochromism, nonlinear optical properties of 3-morpholinobenzanthrone: Experimental and theoretical study

We report the synthesis of 3-morpholino-9-nitrobenzanthrone (NMB) dye. By using FT-IR, 1H NMR, and X-ray crystallography, we characterized the molecular structure of the synthesized dye. The structural features of the dye were compared to those of an identical dye without nitro substituents. The push pull kind of benzanthrone dye (NMB) was examined for solvent-dependent photophysical properties. NMB exhibits a large Stokes shift. The polarity plots indicate that hydrogen-bonding interactions are influential in most of the solvents. Detailed structural analysis as well as one-photon absorption and emission process was computationally investigated for both the molecules. NMB exhibits significant two photon absorption (TPA) activity at various electron transitions ranging from visible to NIR regions. Further, Nonlinear absorption coefficient was calculated for the dye samples from the open aperture Z-scan data. The nonlinear absorption coefficient values were obtained for the dye samples for input laser pulse energies ranging from 5 to 20 µJ. The results decipher that these dye samples are prospective contenders for the fabrication of optical limiter devices. Nitro substituents at the active site enhance charge transfer, thereby enhancing the NLO response.

Nanosecond pulsed laser induced efficient photophoresis actuating of graphene sponge

Photophoresis actuating shows great potentials in cross-scale light-driven manipulation and fuel-free flight due to efficient conversion of light-to-work. However, photophoresis actuating with rapid light response is rarely reported although it is important in light-driven manipulation. In this work, the pulsed laser induced photophoresis of graphene sponge material (PLPGS) is investigated by a homemade sensitive detection system, and the actuating force is measured quantitatively by an optical lever method. The macroscale graphene sponge material can be driven by a 3–5 ns single laser pulse reproducibly. The actuating force is 1.8 μN when the input laser pulse energy density is 4.0 mJ/cm2, and the PLPGS can be triggered by ultra-low laser pulse energy below 70 μJ/cm2. The PLPGS is proved to be quick-response, repeatable, low-energy, and non-destructive.

Spectral and intensity control of high energy terahertz radiation from bulk liquids

High power, broadband terahertz (THz) radiation from liquids, excited by intense, femtosecond 800 nm laser pulses has been demonstrated recently, overturning the long held belief that liquids would not give such emission due to their absorption in the THz region. Given the widespread interest in the use of THz radiation for several applications and the energy and bandwidth limitations of existing sources, liquids are expected to attract great attention in the future. While the emission at tens of microjoules from liquids is very promising, it is important to explore whether control of the THz flux and spectrum is achievable by manipulating the laser or liquid parameters. In this paper we present results on manipulating the spectrum of THz radiation from liquids by chirping the input laser pulse and optimizing the THz output energy by laser chirp as well as optimizing the focal position. We demonstrate tunability by varying the chirp of the laser pulse and show that the THz emission predominantly comes from the region near the end of the liquid path, consistent with the absorption of THz radiation by liquids. This control gives us an opportunity to tune the THz radiation to suit experimental needs. We present simulations that support the results.

Ultrafast dynamics of exciton–polariton in optically tailored potential landscapes at room temperature

In this work, by using femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of confined exciton–polaritons in an optical induced potential well based on a ZnO whispering-gallery microcavity is explicitly visualized. The sub-picosecond transition between succeeding quantum harmonic oscillator states can be experimentally distinguished. The landscape of the potential well can be modified by the pump power, the spatial distance and the time delay of the two input laser pulses. Clarifying the underlying mechanism of the polariton harmonic oscillator is interesting for the applications of polariton-based optoelectronic devices and quantum information processing.

Distinguishing Resonant from Non-Resonant Nonlinear Optical Processes Using Intensity–Intensity Correlation Analyses

Three-color coherent anti-Stokes Raman scattering (CARS) represents non-degenerate four wave mixing that includes both non-resonant and resonant processes, the contributions of which depend upon how the molecular vibrational modes are being excited by the input laser pulses. The scattering signal due to resonant processes builds up progressively. An advanced analytical tool to reveal this deferred resonant signal buildup phenomenon is in need. In this work, we adapt a quantitative analytical tool by introducing one-dimensional and two-dimensional intensity-intensity correlation functions in terms of a new variable (probe pulse delay) and a new perturbation parameter (probe pulse linewidth). In particular, discrete diagonal directional sums are defined here as a tool to reduce both synchronous and asynchronous two-dimensional correlation spectroscopy (2D-COS) maps down to one-dimensional plots while maintaining the valuable analytical information. Detailed analyses using the all-Gaussian coherent Raman scattering closed-form solutions and the representative experimental data for resonant and non-resonant processes are presented and compared. The present work holds a promising potential for industrial application, e.g., by extractive industries to distinguish hydrocarbons (chemically resonant substance) from water (non-resonant contaminant) by utilizing the one- and two-dimensional correlation analyses.

Broadening, nonlinear filtering, and compression of microjoule energy laser pulses at 1 µm wavelength

In this work, we experimentally demonstrate the generation of 30 nm of spectral broadening in a bulk cadmium sulfide (CdS) semiconductor generated by a 280 fs long pulse at 1.024 µm wavelength and with a microjoule energy level. Using second-harmonic generation in barium borate, the complex ring pattern induced by self-focusing due to the strong nonlinear interaction of the laser pulse in the pair of CdS crystals is filtered out using second-harmonic nonlinear crystal to recover a Gaussian shape spatial profile. We also present the temporal compression of the resulting 512 nm laser pulse up to 45 fs by using a pair of standard transmissive gratings, leading to a pulse compression factor of 6.13. This technique is compact, inexpensive, and robust and produces ultrafast optical pulses from an input laser pulse whose duration and energy range are generally incompatible with a straightforward compression method in nonlinear optical fibers.

Cross-polarized wave-generation-based single-shot fourth-order autocorrelator.

A single-shot fourth-order autocorrelator based on cross-polarized wave generation (XPW) is proposed for the temporal contrast measurement, where the XPW process has the advantages of higher energy conversion efficiency, more compact setup, and less sensitivity to misalignment in comparison to the self-diffraction process. The measurement dynamic of 1012 is obtained with only 6 mJ input laser pulse, where the input beam for XPW is focused by a cylindrical lens and XPW signal with the energy of 400 µJ and time duration of 27.2 fs is obtained. Furthermore, beta-barium borate crystal with the thickness of 6 mm and cutting angle of 56° is used for the sum-frequency generation process to benefit the correlation efficiency. The compact setup could help explore the temporal contrast property of the high-power laser pulse.

Stimulated Rayleigh–Bragg scattering study in a two-photon absorbing liquid and a solid

Stimulated Rayleigh–Bragg scattering (SRBS) in highly two-photon active chromophores’ solutions and in a doped polymer rod has been investigated. Under optimized experimental conditions, the energy conversion efficiency from the input 816-nm and ∼ 10 - n s pump pulses to the backward SRBS pulses was up to η = 58 % in the solution of AF450 chromophore in methyl methacrylate (MMA) liquid of 0.001 M concentration, while for the AF450 doped poly(methyl methacrylate) rod of the same concentration the measured value was only η = 0.16 % . Considering that the two-photon absorption properties of the chromophore molecules are basically the same in both cases, the above-mentioned results strongly suggested that the formation of the induced Bragg grating in a solution is mainly due to spatial redistribution of the dopant molecules driven by two-photon resonance enhanced gradient force. In contrast, the same dopant molecules are “frozen” in a solid matrix which prohibits the spatial redistribution of these molecules from forming an effective Bragg grating. Based on the high efficiency of backward SRBS generation as well as the coexisting two-photon absorption, the intense input laser beam will undergo a much stronger nonlinear attenuation. For the tested AF450/MMA solution sample of 0.004 M concentration, when the input laser pulse energy changed from 0.06 mJ to 3.7 mJ, the measured nonlinear transmissivity decreased from 0.82 to 0.11, showing a superior nonlinear attenuation performance with regard to the input pump laser beam.

Study on the correlation between external plasma plumes and stress distribution inside a target immediately after surface laser loading

Dynamic stress wave processes in targets driven by laser-induced plasma determines the mechanical performance of the targets during laser shock peening. In this paper, an optically transparent material is used as a target to detect the distribution of stress waves in situ. Laser-induced plasma and corresponding stress waves are quantitatively analyzed based on interference imaging technology. The evolution of the plasma and stress waves for different laser temporal profiles is studied. The tensile stress in the lower density region behind the main shock front is directly observed. The experimental results show that the laser-induced plasma’s development mode can be significantly changed by adjusting the input laser pulse’s time profile. At the same time, the tensile stress in the lower density region behind the main shock front is reduced, which attenuates the positive effect of laser shock peening.

Multicycle terahertz pulse generation by optical rectification in LiNbO3, LiTaO3, and BBO crystals

We report multicycle, narrowband, terahertz radiation at 14.8 THz produced by phase-matched optical rectification of femtosecond laser pulses in bulk lithium niobate (LiNbO3) crystals. Our experiment and simulation show that the output terahertz energy greatly enhances when the input laser pulse is highly chirped, contrary to a common optical rectification process. We find this abnormal behavior is attributed to a linear electro-optic (EO) effect, in which the laser pulse propagating in LiNbO3 is modulated by the terahertz field it produces, and this in turn drives optical rectification more effectively to produce the terahertz field. This resonant cascading effect can greatly increase terahertz conversion efficiencies when the input laser pulse is properly pre-chirped with additional third order dispersion. We also observe similar multicycle terahertz emission from lithium tantalate (LiTaO3) at 14 THz and barium borate (BBO) at 7 THz, 10.6 THz, and 14.6 THz, all produced by narrowband phase-matched optical rectification.

Polarization-orthogonal filament array induced by birefringent crystals in air

We demonstrate the generation of filament array with orthogonal polarizations in air by using specifically designed wedge-type birefringent quartz plates. Experimental results show that the number of the generated filaments can be expressed as N = 2n wherenis the number of quartz plates inserted in the laser propagation path. By manipulating the optic axis of the quartz plates with respect to the polarization direction of the input laser pulse, the generated filaments can be separated into two parts with the polarization directions perpendicular with each other. The separation distance between the adjacent filaments is found to be linearly dependent on the focal length of external focusing lens. Our results provide a simple and efficient way to generate regular and reproductive femtosecond filament array in air.

Pulse stretcher with two beamsplitting elements for excimer laser pulses.

A pulse stretcher with two beamsplitting elements and an optical ring cavity is proposed. With a two-beamsplitting-element configuration, the temporal profile of the stretched output pulse is effectively improved, and the transient peak power is significantly reduced. By optimizing the radius of curvature of the concave mirrors used in the ring cavity, the spatial profile of the stretched pulse is kept nearly unchanged. The performance of the pulse stretcher is experimentally investigated with a 193 nm excimer laser. By optimizing the splitting ratios of the two beamsplitting elements, the pulse width is extended from 15.5 ns to 46.2 ns with a stretching ratio of 2.89; the transient peak power of the stretched pulse is reduced to 27% of that of the input laser pulse; an energy transmission efficiency of 87.8% is achieved for the proposed pulse stretcher with two beamsplitting elements.