Analytical solution to incident angle quasi-phase-matching engineering for second harmonic generation in a periodic-poled lithium niobate crystal

Phase matching or quasi-phase matching(QPM)is of significant importance to the conversion efficiency of second harmonic generation(SHG)in artificial nonlinear crystals like lithium niobate(LN)crystal or microstructured nonlinear crystals like periodic-poled lithium niobate(PPLN)crystals.In this paper,we propose and show that the incident angle of pump laser light can be harnessed as an alternative versatile tool to engineer QPM for high-efficiency SHG in a PPLN crystal,in addition to conventional means of period adjusting or temperature tuning.A rigorous model is established and analytical solution of the nonlinear conversion efficiency under the small and large signal approximation theory is obtained at different incident angles.The variation of phase mismatching and walk-off length with incident angle or incident wavelength are also explored.Numerical simulations for a PPLN crystal with first order QPM structure are used to confirm our theoretical predictions based on the exact analytical solution of the general large-signal theory.The results show that the narrow-band tunable SHG output covers a range of 532 nm–552.8 nm at the ideal incident angle from 0°to 90°.This theoretical scheme,fully considering the reflection and transmission at the air-crystal interface,would offer an efficient theoretical system to evaluate the nonlinear frequency conversion and help to obtain the maximum SHG conversion efficiency by selecting an optimum incident wavelength and incident angle in a specially designed PPLN crystal,which would be very helpful for the design of tunable narrow-band pulse nanosecond,picosecond,and femtosecond laser devices via PPLN and other microstructured LN crystals.

Experimental Analysis of Radial Centrifugal Pump Shutdown

Centrifugal pumps are widely used in the metallurgy,coal,and building sectors.In order to study the hydraulic characteristics of a closed impeller centrifugal pump during its shutdown in the so-called power frequency and frequency conversion modes,experiments were carried to determine the characteristic evolution of parameters such as speed,inlet and outlet pressure,head,flow rate and shaft power.A quasi-steady-state method was also used to further investigate these transient behaviors.The results show that,compared to the power frequency input,the performance parameter curves for the frequency conversion input are less volatile and smoother.The characteristic time is longer and the response to shutdown is slower.The quasi-steady-state theoretical head-flow curves match the experimental head-flow curves more closely at low flow rates when the frequency conversion input is considered.Moreover,in this case,the similarity law predicts the hydraulic performance more accurately.

A transceiver frequency conversion module based on 3D micropackaging technology

The idea of Ku-band transceiver frequency conversion module design based on 3D micropackaging technology is proposed. By using the double frequency conversion technology,the dual transceiver circuit from Ku-band to L-band is realized by combining with the local oscillator and the power control circuit to complete functions such as amplification, filtering and gain. In order to achieve the performance optimization and a high level of integration of the Ku-band monolithic microwave integrated circuits(MMIC) operating chip, the 3 D vertical interconnection micro-assembly technology is used. By stacking solder balls on the printed circuit board(PCB), the technology decreases the volume of the original transceiver to a miniaturized module. The module has a good electromagnetic compatibility through special structure designs. This module has the characteristics of miniaturization, low power consumption and high density, which is suitable for popularization in practical application.

Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay

This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet （UV） output energy of 0.32 mJ centered at 270 nm with spectral bandwidth of 2 nm when input beam at 800 nm was 70 fs pulse duration and 6 mJ pulse energy which was extracted from Ti：sapphire laser system by a diaphragm, corresponding to an 800-to-270 nm conversion efficiency of 5.3% and a factor-of-l.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18 mJ from a Ti：sapphire laser system was used and optimized, the UV emission could reach 0.83 mJ.

Multiple frequency conversion via atomic spin coherence of storing a light pulse

We experimentally demonstrate multiple frequency conversion via atomic spin coherence of storing a light pulse in a doped solid. The essence of this multiple frequency conversion is four-wave mixing based on stored atomic spin coherence. Through electromagnetically induced transparency, an input probe pulse is stored into atomic spin coherence by modulating the intensity of the control field. By using two different control fields to interact with the coherently prepared medium, the stored atomic spin coherence can be transformed into three different information channels. Multiple frequency conversion is implemented efficiently by manipulating the spectra of the control fields to scatter atomic spin coherence. This multiple frequency conversion is expected to have potential applications in information processing and communication network.

Noise-free frequency conversion of quantum states

In this paper, the frequency conversion of quantum states based on the intracavity nonlinear interaction is proposed. The fidelity of an input state after frequency conversion is calculated, and it is shown the noise-free frequency conversion of a quantum state can be achieved by injecting a strong signal field. The dependences of conversion efficiency on the pump parameter, extra losses and input state amplitude are also analysed.

Quantum frequency doubling based on tripartite entanglement with cavities

We analyze the entanglement characteristics of three harmonic modes, which are the output fields from three cav- ities with an input tripartite entangled state at fundamental frequency. The entanglement properties of the input beams can be maintained after their frequencies have been up-converted by the process of second harmonic generation. We have calculated the parametric dependences of the correlation spectrum on the initial squeezing factor, the pump power, the trans- naission coefficient, and the normalized analysis frequency of cavity. The numerical results provide references to choose proper experimental parameters for designing the experiment. The frequency conversion of the multipartite entangled state can also be applied to a quantum communication network.

Nonreciprocal Single Photon Frequency Conversion via Chiral Coupling between a V-Type System and a Pair of Waveguides

The single photon frequency conversion is investigated theoretically in the system composed of a V-type system chiral coupling to a pair of waveguides. The single photon scattering amplitudes are obtained using the real-space Hamiltonian. The calculated results show that the probability of single photon frequency down-or up-conversion can reach a unit by choosing appropriate parameters in the non-dissipative system with perfect chiral coupling.We present a nonreciprocal single photon beam splitter whose frequency of the output photon is different from that of the input photon. The influences of dissipations and non-perfect chiral coupling on the single frequency conversion are also shown. Our results may be useful in designing quantum devices at the single-photon level.

Rigorous solution to second harmonic generation considering transmission and reflection of light at air–crystal interface

Considering the transmission and reflection of TE-polarized pump light at the air–crystal interface,the second harmonic generation(SHG)in a lithium niobate(LN)crystal is investigated theoretically and systematically in this work.In previous studies,the theoretical analyses of reflection and transmission of incident wave in the process of nonlinear frequency conversion were not considered in LN crystal on account of the complicated calculations.First,we establish a physical picture describing that a beam of light in TE mode transports in the LN crystal considering transmission and reflection at the crystal surface and generates nonlinear second-order optical polarization in crystal.Then we analytically derive the reflection coefficient and transmission coefficient of pump light by using the dispersion relationships and electromagnetic boundary conditions.We construct the nonlinear coupled wave equations,derive and present the small signal approximation solution and the general large signal solution exactly.Under the transmission model and reflection model,we find that the conversion efficiency of the second-harmonic wave is obviously dependent on transmission coefficient and other general physical quantities such as the length of LN crystal and the amplitude of pump light.Our analytical theory and formulation can act as an accurate tool for the quantitative evaluation of the SHG energy conversion efficiency in an LN crystal under practical situations,and it can practically be used to treat other more complicated and general nonlinear optics problems.

Theoretical analysis of frequency modulation-to-amplitude modulation on the final optics and target of the SG Ⅱ-Up laser facility

Frequency modulation(FM)-to-amplitude modulation(AM) conversion is an important factor that affects the time±power curve of inertial confinement fusion(ICF) high-power laser facilities. This conversion can impact uniform compression and increase the risk of damage to optics. However, the dispersive grating used in the smoothing by spectral dispersion technology will introduce a temporal delay and can spatially smooth the target. The combined effect of the dispersive grating and the focusing lens is equivalent to a Gaussian low-pass filter, which is equivalent to 8 GHz bandwidth and can reduce the intensity modulation on the target to below 5% with 0.3 nm @ 3 GHz + 20 GHz spectrum phase modulation. The results play an important role in the testing and evaluating of the FM-to-AM on the final optics and the target, which is beneficial for comprehensively evaluating the load capacity of the facility and isentropic compression experiment for ICF.

Stability of Oil Film and Output Speed of Hydroviscous Drive Affected by the Pressure of Control Oil

Based on the theories of hydraulics and nonlinear control system, the model of hydroviscous drive (HVD) was established, the influences of small ripple of control oil pressure on the output speed of HVD and the stability of oil film between friction disks were analyzed. The conclusion presents that when the frequency of the control oil's pressure ripple is higher than 60?Hz and the peak is less than 0 05?MPa, HVD can work stably. The result is useful for studying the application of frequency conversion technology in regulation of control oil pressure.

Tunable, continuous-wave single-resonant optical parametric oscillator with output coupling for resonant wave

We present a continuous-wave singly-resonant optical parametric oscillator with 1.5% output coupling of the reso- nant signal wave, based on an angle-polished MgO-doped periodically poled lithium niobate （MgO：PPLN）, pumped by a commercial Nd：YVO4 laser at 1064 nm. The output-coupled optical parametric oscillator delivers a maximum total output power of 4.19 W with 42.8% extraction efficiency, across a tuning range of 1717 nm in the near- and mid-infrared region. This indicates improvements of 1.87 W in output power, 19.1% in extraction efficiency and 213 nm in tuning range exten- sion in comparison with the optical parametric oscillator with no output coupling, while at the expense of increasing the oscillation threshold by a factor of - 2. Moreover, it is confirmed that the finite output coupling also contributes to the reduction of the thermal effects in crystal.

β-BaB_(2)O_(4) with special cut-angle applied to single crystal cascaded third-harmonic generation

High-efficiency single crystal cascaded third-harmonic generation(THG)was realized inβ-BaB_(2)O_(4)(BBO)material with special cut-angle.By analyzing effective nonlinear optical coefficient(d_(eff))of the cascaded THG process,which was composed by type-II frequency doubling and type-I sum-frequency,the optimum phase matching(PM)direction in BBO crystal was determined to be(θ=32.1°,φ=11°).With an optimized 9-mm long sample which was processed along this direction,the highest cascaded THG conversion efficiency reached 42.3%,which is much superior to the similar components reported previously,including ADP,KDP,and Gd_(x)Y_(1-x)COB crystals.

Studies on convergence and scaling law of Thomson backscattering spectra in strong fields

With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for the plane wave laser field without and with applied external constant magnetic field. Some unclear points appeared in previous work are clarified. The extension of the method to a general situation for the laser field with an arbitrary polarization is discussed. We also make a simple analysis and discussion about the optimal spectra dependence of field parameters and its implication to practical applications.

High-energy picosecond single-pass multi-stage optical parametric generator and amplifier

We demonstrate a new management of multi-stage optical parametric generator(OPG)and amplifier(OPA)to obtain high-energy picosecond sources with high beam quality.The setup of multi-stage OPG-OPA requires mode-matching between the pump beam and the stable mode of the OPG-OPA.In a proof-of-principle experiment,the single-pass multi-stage OPG-OPA consists of three walk-off compensated KTP crystal pairs and two lenses,pumped by an 86 ps,1064 nm 10 kHz picosecond laser.The signal light at~1.77μm has an average output power of 502 mW with record energy up to 50.2μJ.The beam quality factor of the signal light can be improved toM^(2)_(x) ×M^(2)_(y)after filtering out about 40%signal power.To the best of our knowledge,it is the first picosecond single-pass multi-stage OPG-OPA pumped at kHz regime.

Cascade correlation-enhanced Raman scattering in atomic vapors

A new Raman process can be used to realize efficient Raman frequency conversion by coherent feedback at low light intensity [Chen B, Zhang K, Bian C L, Qiu C, Yuan C H, Chen L Q, Ou Z Y, and Zhang W P 2013 Opt. Express 21, 10490]. We present a theoretical model to describe this enhanced Raman process, termed as cascade correlation-enhanced Raman scattering, which is a Raman process injected by a seeded light field. It is correlated with the initially prepared atomic spin excitation and driven by the quasi-standing-wave pump fields, and the processes are repeated until the Stokes intensities are saturated. Such an enhanced Raman scattering may find applications in quantum information, nonlinear optics, and optical metrology due to its simplicity.

A 515-nm laser-pumped idler-resonant femtosecond BiB_(3)O_(6) optical parametric oscillator

We report on an idler-resonant femtosecond optical parametrical oscillator(OPO)based on BiB_(3)O_(6)(BiBO)crystal,synchronously pumped by a frequency-doubled,mode-locked Yb:KGW laser at 515 nm.The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm.At a repetition rate of 75.5 MHz,the OPO generates as much as 400 mW of idler power with 3.1 W of pump power,the corresponding pulse duration is 80 fs,which is 1.04 times of Fourier transform-limited(FTL)pulse duration at 1305 nm.In addition,the OPO exhibits excellent beam quality with M^(2)<1.8 at 1150 nm.To the best of our knowledge,this is the first idler-resonant femtosecond OPO pumped by 515 nm.

Enhancement of the second harmonic generation from monolayer WS_(2) coupled with a silica microsphere

Monolayer transition metal dichalcogenides(TMDs) are widely used for integrated optical and photoelectric devices.Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation(SHG) from monolayer tungsten sulfide(WS2) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.

Millimeter-Wave Heterodyne Six-Port Receiver:New Implementation and Demodulation Results

This paper presents a new implementation of a millimeter-wave heterodyne receiver based on six-port technology. The six-port model is implemented in Advanced Design System （ADS） using S-parameter measurements for realistic advanced simulation of a short-range 60 GHz wireless link. Millimeter-wave frequency conversion is performed using a six-port down-converter. The second frequency conversion is performed using conventional means because of low IF. A comparison between the proposed receiver and a conventional balanced millimeter-wave mixer shows that the proposed receiver improves conversion loss and I/Q phase stability over the local oscillator （LO） and RF power ranges. The results of demodulating a V-band quadrature phase-shift keying （QPSK） signal at a high data rate of 100 Mb/s-1 Gb/s are discussed. The results of a bit error rate （BER） and error vector magnitude （EVM） analysis prove that the proposed architecture can be successfully used for wireless link transmission up to 10 m.

High-dimensional frequency conversion in a hot atomic system

One of the major difficulties in realizing a high-dimensional frequency converter for conventional optical vortex(COV)modes stems from the difference in ring diameter of the COV modes with different topological charge numbers l.Here,we implement a high-dimensional frequency converter for perfect optical vortex(POV)modes with invariant sizes by way of the four-wave mixing(FWM)process using Bessel–Gaussian beams instead of Laguerre–Gaussian beams.The measured conversion efficiency from 1530 to 795 nm is independent of l at least in subspace l∈{-6,………,6},and the achieved conversion fidelities for two-dimensional(2D)superposed POV states exceed 97%.We further realize the frequency conversion of 3D,5D,and 7D superposition states with fidelities as high as 96.70%,89.16%,and 88.68%,respectively.The proposed scheme is implemented in hot atomic vapor.It is also compatible with the cold atomic system and may find applications in high-capacity and long-distance quantum communication.