Pump Beam Research Articles

Compact generation scheme of path–frequency hyperentangled photons using 2D periodical nonlinear photonic crystal

Hyperentanglement is a promising resource for achieving high capacity quantum communication. Here, we propose a compact scheme for the generation of path–frequency hyperentangled photon pairs via spontaneous parametric down-conversion (SPDC) processes, where six different paths and two different frequencies are covered. A two-dimensional periodical χ (2) nonlinear photonic crystal (NPC) is designed to satisfy type-I quasi-phase-matching conditions in the plane perpendicular to the incident pump beam, and a perfect phase match is achieved along the pump beam’s direction to ensure high conversion efficiency, with theoretically estimated photon flux up to 2.068 × 105 pairs⋅s−1⋅mm−2. We theoretically calculate the joint-spectral amplitude (JSA) of the generated photon pair and perform Schmidt decomposition on it, where the resulting entropy S of entanglement and effective Schmidt rank K reach 3.2789 and 6.4675, respectively. Our hyperentangled photon source scheme could provide new avenues for high-dimensional quantum communication and high-speed quantum information processing.

Quasi-phase matching using frozen waves without periodic poling.

In this article, we show that quasi-phase matching can be accomplished by manipulating one of the pump beams without any periodic poling. We analyze a simple case wherein one of the interacting beams has a periodic pattern, and the others are assumed to be planewaves. We present comparisons of the efficiency of some nonlinear processes with quasi-phase matching achieved through our method and the conventional method. We demonstrate that some patterns of the pump beam can be more efficient than conventional periodic poling.

Study on the effect of pump beam on the purity of high-order HG mode in off-axis pumped Tm:YLF laser

In this paper, the effect of the pump beam radius on the purity of the HG modes is investigated based on the off-axis pumped Tm:YLF laser, and LG mode vortex laser of 1.9 μm is realized. The multi-mode rate equations are established to reveal that a smaller pump beam radius leads to higher purity of the HG mode beam. At the same time, it is experimentally found that each HG mode alternated with increasing off-axis displacement at a pump beam radius of 200 μm, with a purity of 87.9 % for the HG8,0 mode. However, at the pump beam is 400 μm, the phenomenon of multiple HG modes output increases in the process of adjusting the off-axis displacement. The consistency between the experimental and theoretical results proves the effect of the size of the pump beam on the purity of the high-order HG mode laser. The 1.9 μm LG vortex beam within the 8th order is achieved with a pump beam radius of 200 μm, and the slope efficiency of the LG1,0 mode could reach 34.51 %.

Selection and Application of Beam Pumping Unit for Heavy Oil Production

Beam pumping units were among the first and are still among the most widely used artificial lift systems. This study investigates the components of beam pumping units and the manufacturing mechanism and design procedure recommended by Recommended Practice and the QRod simulator. The API provides API RP 11L Recommended Practice to obtain the values and operating characteristics for each component in dimensionless form. A trial-and-error method is used during the design procedures to determine the best surface and subsurface equipment for a given well's data. When completing a well, the artificial lift method must be considered to ensure that the well is able to be produced at a satisfactory rate. Besides, the procedures created nine cases to compare the requirements of different production rates and depths for a heavy oil well with 14 APIs. A depth of 5,000 ft with a rate of 300 bbl/day and a depth of 7,000 ft with a rate of 500 bbl/day is the specific production rate and depths at which the well will produce. For 300 BBL/Day the tubing size selected was 2-7/8” OD, for this size the suitable plunger size is 2”, and the suitable stroke length was 74in. In cases 6, 8, and 9, all the simulated rod strings were unable to handle the stress imposed by the combination of high depth and high production rate. As a result, all designed systems will fail during production.

A comparative study of electromagnetically induced transparency (EIT) in Λ-, V-, and Ξ-type systems using Laguerre–Gaussian (LG) laser beams

In this paper, a theoretical investigation of electromagnetically induced transparency (EIT) using Laguerre–Gaussian (LG) beams has been carried out for the three canonical atom-laser coupled systems (e.g. [Formula: see text]-, V-, and [Formula: see text]-type) in [Formula: see text]Rb atom. The required optical Bloch equations (OBEs) are derived for each system. The OBEs are analytically solved in steady-state condition under the weak probe field approximation. We have used the iterative perturbative technique to obtain the probe coherence term. The probe response w.r.t. probe detuning for different orders of the orbital angular momentum (OAM) number of both the pump and probe LG beams has been studied. We have also studied the effect of the OAM number on probe response in both Doppler-free and Doppler-broadened mediums. It has been observed that the EIT signal is squeezed for nonzero OAM number of the pump beam with arbitrary OAM number of the probe beam. It is found that for higher-order OAM number, the EIT signal is further squeezed. The modification of the EIT signal is attributed because of the spatial-dependent Rabi frequency. Our study demonstrates that the dynamic of the probe field inside an atomic medium may be controlled by tuning the OAM number of the LG beam.

SERF-like magnetometry in room-temperature environment.

We demonstrate an atomic magnetometry using amplitude-modulated pumping and hyperfine repumping techniques in a paraffin-coated cell. By exploiting the constructive interference between spins polarized by the pump beam and an additional repump beam, we observe a three-fold increase in the amplitude of magnetic resonance, along with a reduction in linewidth by approximately two times. The implementation of the repump beam effectively narrows the linewidth, demonstrating successful suppression of spin-exchange relaxation. This reduction in relaxation rate, combined with the enhanced signal, significantly improves the sensitivity of the magnetometer. Consequently, our technique offers a promising approach for achieving SERF-like magnetometry with sub-fT-level sensitivity in Earth-field range and room-temperature environment.

Effects of ion trapping and fluctuations of electron temperature and plasma flow on cross-beam energy transfer

The influences of ion trapping and fluctuations of electron temperature and plasma flow on cross-beam energy transfer (CBET) are examined using two- and three-dimensional particle-in-cell simulations in parameter regimes relevant to recent CBET experiments at the OMEGA laser facility. In mid-Z plasma irradiated by an intense pump beam and weaker probe beam, ion trapping, collisional de-trapping, and plasma flow induced by thermal effects are shown to affect the CBET gain. Ion trapping can enhance or detune the CBET resonance [Nguyen et al., Phys. Plasmas 28, 082705 (2021)]. Collisional de-trapping can affect the CBET gain at low seed beam intensity near the onset threshold for ion trapping. Thermal-effects-induced flow can also detune the CBET resonance at a level comparable to that from trapping at low seed beam intensity. As a consequence, the CBET gain is sensitive to collisions and dimensionality at low seed beam intensity where ion trapping is weak but is insensitive to collisions and dimensionality at high seed beam intensity where ion trapping is strong.

Probe Beam Dichroism and Birefringence in Stimulated Raman Scattering in Polyatomic Molecules.

Dichroism and birefringence in Stimulated Raman Scattering (SRS) in polyatomic molecules were studied theoretically. General expressions describing the change of the polarization matrix of the probe laser beam transmitted through initially isotropic molecular sample excited by the pump laser beam have been derived. Arbitrary polarization states and propagation directions of the incoming pump and probe beams were considered. The expressions were written in terms of spherical tensor operators that allowed for separation of the field polarization tensor and the molecular part containing three scalar values of nonlinear optical susceptibility with =0,1,2. The geometry of almost collinear propagation of the pump and probe beams through the molecular sample was considered in greater details. It was shown that the dichroism and birefringence refer to the nonlinear optical susceptibility element and that their contributions to the SRS signal can be separated experimentally by using an appropriate probe beam polarization analyzer installed in front of the photodetector. Particular cases of the off-resonant SRS and resonant SRS have been considered. The results obtained were expressed in terms of the Stokes polarization parameters of the pump and probe beams.

Directional planar antennae in polariton condensates

We report on the realization of all-optical planar microlensing for exciton–polariton condensates in semiconductor microcavities. We utilize spatial light modulators to structure a nonresonant pumping beam into a plano–concave lens-shape focused onto the microcavity plane. When pumped above condensation threshold, the system effectively becomes a directional polariton antenna, generating an intense focused beam of coherent polaritons away from the pump region. The effects of pump intensity, which regulates the interplay between gain and blueshift of polaritons, as well as the geometry of the lens-shaped pump are studied, and a strategy to optimize the focusing of the condensate is proposed. Our work underpins the feasibility to guide nonlinear light in microcavities using nonresonant excitation schemes, offering perspectives on optically reprogramable on-chip polariton circuitry.

High-power, low noise, high gain few-mode fiber amplifier

The few-mode erbium-doped fiber amplifier (FM-EDFA) is a necessary component for high-capacity long-haul mode-division multiplexing (MDM) fiber optic communication systems. In this paper, an all-fiber few-mode amplifier based on erbium-ytterbium co-doped double-clad fiber is designed and demonstrated. We have developed a fiber-optic pump beam combiner and a few-mode isolator. Combined with the two-stage cascade method, an all-fiber few-mode fiber amplifier with high-power, high-gain and low-noise is realized. Simultaneous amplification of 6 modes (LP01, LP11a, LP11b LP21a, LP21b and LP02) are achieved in the 1535–1565 nm range with average modal gain greater than 40 dB, maximum saturated output power up to 29.5 dBm, differential modal gain (DMG) of ∼3 dB and minimum noise figure (NF) of 4.69 dB.

High-efficiency 261-nm continuous-wave laser by single-blue-laser-diode-pumped Pr3+:LiYF4 crystal

High-power continuous-wave (CW) deep ultraviolet lasers attract growing research interest in the field of optoelectronics. Herein, we perform a CW deep ultraviolet laser at 261 nm by the intracavity frequency doubling of a single-blue-laser-diode-pumped Pr3+:LiYF4 (Pr:YLF) laser. The excellent mode matching between the pump and fundamental-frequency laser beams is realized by optimizing the pump focusing and laser resonator systems. On that basis, the maximum CW fundamental-frequency laser obtained is 1.41 W at 522 nm, corresponding to a slope efficiency of 59.12%. Moreover, a deep ultraviolet laser is further demonstrated at 261 nm using a β-BaB2O4 (BBO) frequency-doubling crystal, yielding a maximum output power of 1.17 W and an optical–optical conversion efficiency of 33.4% with respect to the pump power. Such a result is the highest optical–optical conversion efficiency of the CW DUV lasers from Pr3+-doped crystals, to the best of our knowledge. The finding in this work manifests the development potential of all-solid-state deep ultraviolet lasers and provides a feasible avenue for achieving high-efficiency deep ultraviolet laser output.

Spatial and temporal characteristics of spontaneous parametric down-conversion with varying focal planes of interacting beams

Spontaneous parametric down-conversion (SPDC) is a widely used process to prepare entangled photon pairs. In SPDC, a second-order nonlinear crystal is pumped by a coherent laser beam to generate photon pairs. The photon pairs are usually detected by single-mode fibers (SMF), where only photons in a Gaussian mode can be collected. The collection modes possess typical Gaussian parameters, namely a beam waist and a focal plane position. The collection efficiency of photons highly depends on the choice of both parameters. The exact focal plane position of the pump beam relative to those of the detection modes is difficult to determine in a real experiment. Usually, theoretical and experimental studies assume that the focal plane positions of the pump and the generated beams are positioned in the center of the crystal. The displacement of beam focal planes can lead to deviations from expected results and the coupling efficiency into SMF can decrease. In this study, we theoretically examine variable positions of focal planes in the Laguerre–Gaussian basis, a popular experimental modal decomposition of the spatial biphoton state. We explore how the choice of focal plane positions affects the spatial and temporal properties and the purity of the photon pairs. We present SPDC setups where precise knowledge of the focal plane position is essential and scenarios where focal plane displacements have negligible impact on experimental outcomes.Graphical

Pulse Burst Multiwavelength Terahertz-Wave Spectroscopic Measurement Using Parametric Wavelength Conversion

In this study, we developed a multi-wavelength spectroscopic measurement system using a pulse burst-pumped injection-seeded terahertz (THz)-wave parametric generator (is-TPG). Real-time spectroscopy using multi-wavelength simultaneous generation has been demonstrated; however, the ability to make quantitative measurements with this method has been limited by the gain competition between wavelengths. In this study, we divided the pump beam into multiple paths and created pulse bursts with nanosecond intervals via spatial delays. Quasi-multi-wavelength simultaneous generation was achieved by generating different THz wavelengths with each pulse; in principle, this is equal to repetitive single-wavelength generation. The gain competition between multi-wavelengths was suppressed compared to the multi-wavelength is-TPG pumped by a single pump pulse. Pulse-burst pumping improved the “quantitativeness” of real-time spectroscopic measurements using an is-TPG and is expected to expand the scope of THz wave applications.

Reduction of depolarization loss in a Tm-doped sesquioxide ceramic laser using a ring-shaped pump beam.

We report on a simple method for reduction of the depolarization loss in an end-pumped Tm:Y2O3 ceramic laser by using a near-field ring-shaped pump beam. Initially, we theoretically derive the expression of the depolarization loss in a bulk laser end-pumped with a near-field flat-top-hat or ring-shaped beam, where a significant reduction of depolarization loss in the latter case is presented. Experimental verification is thereafter carried out with a Tm:Y2O3 ceramic laser employing these two different pump configurations. It shows that the experimentally measured depolarization losses are close to the simulated values; the loss in the case of the annular-beam pump is almost 18 times lower than that with a quasi-top-hat beam at a same absorption pump power of 7.4 W. This work, as a proof-of-principle study, indicates that depolarization loss in the end-pumped bulk lasers can be significantly reduced simply by using a ring-shaped pump beam.

Spiking ruby revisited: self-induced periodic spiking oscillations leading to chaotic state in a Cr:Al2O3 laser with cw 532-nm pumping

This paper reexamines a 60-year-old mystery of spiking behavior in ruby lasers with a cw 532-nm pump, paying special attention to mode matching between the pump and lasing beam within a ruby crystal placed in a semi-confocal laser cavity. Periodic spiking oscillations were observed in a limited pump power regime, where spikes obeying the generic asymmetric hyperbolic function appeared at a repetition rate around 50 kHz and with a 130-150 ns width and 0.1-0.6 µJ energy depending on the pump power. The physics of the spiking behavior based on Kleinman’s mechanical approach and a plausible interpretation for the periodic spiking oscillation in terms of self-induced mode matching between the pump and laser beams through the self-induced Kerr-lens effect are addressed. The statistical nature inherent to spiking and the associated self-organized critical behavior in the quasi-periodic spiking oscillations as well as chaotic states occurring outside the periodic spiking regime are clarified from a nonlinear dynamics point of view and intriguing statistical properties inherent to chaotic oscillations in usual solid-state lasers subjected to external modulations are shown to be present in the self-induced instabilities of the ruby laser

Frequency-angular spectrum of entangled photon pairs generated by focused pump

Spontaneous parametric down-conversion (SPDC) is a well-established method for generating entangled photon pairs, and their frequency-angular spectrum properties are of significant interest in various applications. Generally, the focused pump can increase the efficiency of single-mode photons generation, and lead to the asymmetric broadening of the SPDC emission cone relative to plane wave, while our analysis shows it will be further intensified when the pump divergence exceeds 1.3°. In this paper, we propose a theoretical model for accurately ascertaining the frequency-angular spectrum of entangled photon pairs produced by arbitrary pumps, then obtain complete spatial distribution and spectral properties of type I and II SPDC photons, and further demonstrate its validity referring to experimental results of other researchers. Our method is available for high-efficient generation of entangled photon pairs through optimizing crystal orientation, pump beam focus, and detection geometry.

Polarimetric Features of PEPC Polymer Doped with Photoisomerizable SY3 Azodye Chromophore

Photo-induced anisotropy measurements were carried out in thin films of azopolymers PEPC with Solvent Yellow 3, with the concentrations of 10 wt% and 30 wt% of polymers with azo groups in their side-chain. The experimental dependences of the azimuths of the probe beam at the pump beam angles for samples were studied. The photoinduced dependence of the sample birefringence of the probe beam at the incident polarization angle of the pump beam was carried out by the polarimetric method for the studied samples. The geometric phase of anisotropic carbazole-containing azopolymers, in contrast to the dynamic phase, can be measured by the proposed polarimetric method without involving interferometry methods. This is possible because the geometric phase is not controlled by the difference in optical paths but is the result of a change of polarization inside the films due to photoinduced changes in its spatial structure.

Pump-probe reflectivity studies of ultrashort laser-induced acousto-mechanical strains in ZnO films

In the current work we report on the generation of acoustic strains in thin ZnO layers using optoacoustic transduction of ultrashort laser pulses into acoustic waves on an Au thin film transducer. After absorption of energy by the electron system of the metal, energy conversion, thermal expansion and mechanical deformation takes place. The generation and propagation of the induced acoustic strains are monitored in time via a degenerate pump-probe transient reflectivity optical setup at 800 nm, as opposed to most commonly used schemes that employ different wavelengths for the pump and probe beams, mostly in the vicinity of ZnO maximum absorption. The experimental results include energy relaxation times and phonon scattering frequencies and are supported by a thermal vibro-acoustic finite element model. The model is based on the combination of a revised two-temperature approach and elasticity theory, and considers anisotropic properties for the ZnO film and the computation of the elastic wave velocity for the first time. The outcomes are discussed in the context of electron–phonon coupling factors and other material properties. A good agreement between the experimental findings and the results from the numerical simulations has been established, regarding outcomes like the mean velocity of the strain waves, establishing a novel characterization method applicable to a variety of materials and structures.

Neural network-aided optimisation of a radio-frequency atomic magnetometer.

Efficient unsupervised optimisation of atomic magnetometers is a requirement in many applications, where direct intervention of an operator is not feasible. The efficient extraction of the optimal operating conditions from a small sample of experimental data requires a robust automated regression of the available data. Here we address this issue and propose the use of general regression neural networks as a tool for the optimisation of atomic magnetometers which does not require human supervision and is efficient, as it is ideally suited to operating with a small sample of data as input. As a case study, we specifically demonstrate the optimisation of an unshielded radio-frequency atomic magnetometer by using a general regression neural network which establishes a mapping between three input variables, the cell temperature, the pump beam power and the probe beam power, and one output variable, the AC sensitivity. The optimisation results into an AC sensitivity of 44 fT/Hz at 26 kHz.

High-efficiency Ho:YAG single-crystal fiber laser in-band pumped by a 1.9 μm laser diode

We report on a 10-watt-level, efficient 2 μm Ho:YAG (0.6 at.% Ho3+ doped Y3Al5O12) single crystal fiber (SCF) laser in-band pumped by a 1.9 μm laser diode. Benefiting from the high gain of the SCF and the unique propagation features of the pump and laser beams, a maximum output power of 10.77 W is achieved with T OC = 20%, corresponding to a slope efficiency of 61.8%. The higher efficiency of 64.8% and the output power of 9.8 W are obtained with T OC = 50%. Compared to the traditional bulk crystal, wave-guiding of the pump light in the SCF can extend the gain region and thus improve the laser efficiency, which provides a simple and effective method to improve the utilization rate of the pump light even for the low-brightness laser diodes.