We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are pr...We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.展开更多
A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OC...A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.展开更多
A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded differe...A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.展开更多
High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically pol...High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.展开更多
We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of...We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).展开更多
A novel widely tunable dual-wavelength mid-IR difference frequency generation (DFG) scheme with uniform grating periodically poled lithium niobate (PPLN) is presented in this paper. By using the temperature-depend...A novel widely tunable dual-wavelength mid-IR difference frequency generation (DFG) scheme with uniform grating periodically poled lithium niobate (PPLN) is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching (QPM) peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.展开更多
Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe c...Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-Ⅰ phase matching scheme and 730 W for type-Ⅱ phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.展开更多
Effects of second harmonic generation (SHG) and cascaded second harmonic generation/difference frequency generation(cSHG/DFG) based on the quasi-phase-matching (QPM) condition in periodically poled lithium nioba...Effects of second harmonic generation (SHG) and cascaded second harmonic generation/difference frequency generation(cSHG/DFG) based on the quasi-phase-matching (QPM) condition in periodically poled lithium niobate (PPLN) waveguide were investigated experimentally. SHG conversion efficiency of -13.6dB and QPM bandwidth of 0.45nm were achieved using a 16.1dBm power of fundamental wave at 1550.4nm. Using pulsed all-fiber passive mode locked laser and tunable continuous wave laser, cSHG/DFG effect utilized for optical sampling was observed. Conversion efficiencies were calculated, and 11.88nm-wide QPM bandwidth was achieved through changing the wavelength of input signal. Conversion efficiency of cSHG/DFG effect increased linearly with the total injected power.展开更多
We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators (OPO) in different wavelength tuning ...We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators (OPO) in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous dif- ference frequency generation (DFG) process by monolithic aperiodically poled, magnesium oxide doped lithium niobate (APMgLN) crystals. The APMgLN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMgLN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal work- ing conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 p_J and 700 ~J are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMgLN crystal is optimized according to this pump condition. To the best of our knowledge, this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMgLN crystals.展开更多
We report on a new scheme for efficient continuous-wave(CW)mid-infrared generation using difference frequency generation(DFG)inside a periodically poled lithium niobate(PPLN)-based optical parametric oscillator(OPO).T...We report on a new scheme for efficient continuous-wave(CW)mid-infrared generation using difference frequency generation(DFG)inside a periodically poled lithium niobate(PPLN)-based optical parametric oscillator(OPO).The pump sources were two CW fiber lasers fixed at 1018 nm and 1080 nm.One worked as the assisted laser to build parametric oscillation and generate an oscillating signal beam while the other worked at low power(3 W)to induce DFG between it and the signal beam.The PPLN temperature was appropriately adjusted to enable OPO and DFG to synchronously meet phase-matching conditions.Finally,both low-power 1018 nm and 1080 nm pump beams were successfully converted to 3.1μm and 3.7μm idler beams,respectively.The conversion efficiencies of the 1018 nm and 1080 nm pumped DFG reached 20% and 15%,respectively,while their slope efficiencies reached 19.6% and 15%.All these data were comparable to the OPOs pumped by themselves and never realized before in traditional CW DFG schemes.The results reveal that high-efficiency frequency down-conversion can be achieved with a low-power nearinfrared pump source.展开更多
We demonstrated stable midinfrared(MIR) optical frequency comb at the 3.0 μm region with difference frequency generation pumped by a high power, Er-doped, ultrashort pulse fiber laser system. A soliton mode-locked161...We demonstrated stable midinfrared(MIR) optical frequency comb at the 3.0 μm region with difference frequency generation pumped by a high power, Er-doped, ultrashort pulse fiber laser system. A soliton mode-locked161 MHz high repetition rate fiber laser using a single wall carbon nanotube was fabricated. The output pulse was amplified in an Er-doped single mode fiber amplifier, and a 1.1–2.2 μm wideband supercontinuum(SC) with an average power of 205 m W was generated in highly nonlinear fiber. The spectrogram of the generated SC was examined both experimentally and numerically. The generated SC was focused into a nonlinear crystal, and stable generation of MIR comb around the 3 μm wavelength region was realized.展开更多
Graphene-based surface plasmon waveguides(SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs ...Graphene-based surface plasmon waveguides(SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation(DFG) under near-infrared pumps.The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs∕Al Oxstructure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs∕Al Ox waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.展开更多
The progress achieved on power scaling and compact and portable THz sources is reviewed.By reversely stacking the GaP plates,the photon conversion efficiency is improved from 25% to 40% which corresponds to the maximu...The progress achieved on power scaling and compact and portable THz sources is reviewed.By reversely stacking the GaP plates,the photon conversion efficiency is improved from 25% to 40% which corresponds to the maximum value.When the number of the plates is increased from four to five,the output power decreases because of back conversion.The THz generation is also investigated by mixing the two frequencies generated by a single Nd:YLF solid-state laser.The average output power reaches 1 μW.The introduction of two Nd:YLF crystals significantly improves the output power to 4.5 μW.This configuration facilitates the generation of different output frequencies.展开更多
The intensity difference squeezed state, which means that the fluctuation of the intensity difference between signal and idler beams is less than that of the corresponding shot noise level(SNL), plays an important r...The intensity difference squeezed state, which means that the fluctuation of the intensity difference between signal and idler beams is less than that of the corresponding shot noise level(SNL), plays an important role in high sensitivity measurement, quantum imaging, and quantum random numbers generation. When an optical parametric oscillator consisting of a type-Ⅱ phase-matching periodically poled KTiOPO4 crystal operates above the threshold, an intensity difference squeezed state at a telecommunication wavelength can be obtained. The squeezing of 7.7 ± 0.5 dB below the SNL is achieved in an analysis frequency region of 2.4–5.0 MHz.展开更多
We report the investigation on the performance of an amplification assisted difference frequency generation(AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium n...We report the investigation on the performance of an amplification assisted difference frequency generation(AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the reduction in conversion efficiency resulting from wider acceptance bandwidths for the input lasers. We believe that such systems combining the merits of high stability inherited from cavity-free configuration and high efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community,especially when the pulse shaping technique is incorporated.展开更多
Rheumatoid arthritis is a chronic,systemic autoimmune disease predominantly based on joint lesions with an extremely high disability and deformity rate.Several drugs have been used for the treatment of rheumatoid arth...Rheumatoid arthritis is a chronic,systemic autoimmune disease predominantly based on joint lesions with an extremely high disability and deformity rate.Several drugs have been used for the treatment of rheumatoid arthritis,but their use is limited by suboptimal bioavailability,serious adverse effects,and nonnegligible first-pass effects.In contrast,transdermal drug delivery systems(TDDSs)can avoid these drawbacks and improve patient compliance,making them a promising option for the treatment of rheumatoid arthritis(RA).Of course,TDDSs also face unique challenges,as the physiological barrier of the skin makes drug delivery somewhat limited.To overcome this barrier and maximize drug delivery efficiency,TDDSs have evolved in terms of the principle of transdermal facilitation and transdermal facilitation technology,and different generations of TDDSs have been derived,which have significantly improved transdermal efficiency and even achieved individualized controlled drug delivery.In this review,we summarize the different generations of transdermal drug delivery systems,the corresponding transdermal strategies,and their applications in the treatment of RA.展开更多
High-power terahertz(THz) generation in the frequency range of 0.1-10 THz has been a fast-developing research area ever since the beginning of the THz boom two decades ago, enabling new technological breakthroughs in ...High-power terahertz(THz) generation in the frequency range of 0.1-10 THz has been a fast-developing research area ever since the beginning of the THz boom two decades ago, enabling new technological breakthroughs in spectroscopy, communication, imaging,etc. By using optical(laser) pumping methods with near-or mid-infrared(IR) lasers, flexible and practical THz sources covering the whole THz range can be realized to overcome the shortage of electronic THz sources and now they are playing important roles in THz science and technology. This paper overviews various optically pumped THz sources, including femtosecond laser based ultrafast broadband THz generation, monochromatic widely tunable THz generation, single-mode on-chip THz source from photomixing, and the traditional powerful THz gas lasers. Full descriptions from basic principles to the latest progress are presented and their advantages and disadvantages are discussed as well. It is expected that this review gives a comprehensive reference to researchers in this area and additionally helps newcomers to quickly gain understanding of optically pumped THz sources.展开更多
A 125 MHz fiber-based frequency comb source in the mid-infrared wavelength region is presented. The source is based on difference frequency generation from a polarization-maintaining Er-doped fiber pump laser and cove...A 125 MHz fiber-based frequency comb source in the mid-infrared wavelength region is presented. The source is based on difference frequency generation from a polarization-maintaining Er-doped fiber pump laser and covers a spectrum between2900 cm^(-1) and 3400 cm^(-1) with a simultaneous bandwidth of 170 cm^(-1) and an average output power up to 70 m W. The source is equipped with actuators and active feedback loops, ensuring long-term stability of the repetition rate, output power, and spectral envelope. An absorption spectrum of ethane and methane was measured using a Fourier transform spectrometer to verify the applicability of the mid-infrared comb to multispecies detection. The robustness and good long-and short-term stability of the source make it suitable for optical frequency comb spectroscopy of hydrocarbons.展开更多
In this work,azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical(NLO)properties.The sum-over-states(SOS)model based calculations demonstrate that dipolar contrib...In this work,azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical(NLO)properties.The sum-over-states(SOS)model based calculations demonstrate that dipolar contributions are larger than octupolar contributions to the static first hyperpolarizability(〈β0〉)in most nano-graphenes except those with high symmetry(e.g.,a C2v nano-graphene has octupolar contributionsΦJ=3 up to 59.0%of the〈β0〉).Nano-graphenes containing two parallel orientating azulenes(i.e.,Out-P and Out-Ps)have large dipole moments,while their ground state is triplet.Introducing B/N/BN atoms into the positions with a high spin density transfers the ground state of Out-P and Out-Ps to closed-shell singlet,and the Out-Ps-2N has a large〈β0〉of 1621.67×10−30 esu.Further addition of an electron donor(NH2)at the pentagon end enhances the〈β0〉to 1906.22×10−30 esu.The two-dimensional second-order NLO spectra predicted by using the SOS model find strong sum frequency generations and difference frequency generations,especially in the near-infrared and visible regions.The strategies to stabilize the electronic structure and improve the NLO properties of azulene-defect carbon nanomaterials are proposed,and those strategies to engineer nano-graphenes to be semiconducting while maintaining theπ-framework are exten-dable to other similar systems.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274326,61221064,61405222,11134010 and 11127901the Shanghai Sailing Program under Grant No 14YF1406200
文摘We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.
基金the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).
基金Project supported by the National Natural Science Foundation of China(Grant No.11374161)the Open Research Project of Jiangsu Provincial Key Labo-ratory of Meteorological Observation and Information Processing,China(Grant No.KDXS1206)the Project Funded by the Priority Academic Program Development of Jiangsu Provincial Higher Education Institutions,China
文摘A novel widely tunable dual-wavelength mid-IR difference frequency generation (DFG) scheme with uniform grating periodically poled lithium niobate (PPLN) is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching (QPM) peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60777036 and 60671036)the National Basic Research Program of China (Grant No. 2007CB310403)
文摘Using a double resonant KTiOPO4 (KTP) intracavity optical parametric oscillator operating at degenerated point of 2 μm, we demonstrate a unique mid-infrared source based on difference frequency generation in GaSe crystal. The output tuning range is 8.42-19.52 μm, and a peak power of 834 W for type-Ⅰ phase matching scheme and 730 W for type-Ⅱ phase matching scheme are achieved. Experimental results show that this oscillator is a good alternative to the generator of a compact and tabletop mid-infrared radiation with a widely tunable range.
基金Supported by the National Natural Science Foundation of China(6077702460978007)
文摘Effects of second harmonic generation (SHG) and cascaded second harmonic generation/difference frequency generation(cSHG/DFG) based on the quasi-phase-matching (QPM) condition in periodically poled lithium niobate (PPLN) waveguide were investigated experimentally. SHG conversion efficiency of -13.6dB and QPM bandwidth of 0.45nm were achieved using a 16.1dBm power of fundamental wave at 1550.4nm. Using pulsed all-fiber passive mode locked laser and tunable continuous wave laser, cSHG/DFG effect utilized for optical sampling was observed. Conversion efficiencies were calculated, and 11.88nm-wide QPM bandwidth was achieved through changing the wavelength of input signal. Conversion efficiency of cSHG/DFG effect increased linearly with the total injected power.
基金supported by the National Natural Science Foundation of China(Grant No.61505236)the Innovation Program of Shanghai Institute of Technical Physics,China(Grant No.CX-2)the Program of Shanghai Subject Chief Scientist,China(Grant No.14XD1404000)
文摘We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators (OPO) in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous dif- ference frequency generation (DFG) process by monolithic aperiodically poled, magnesium oxide doped lithium niobate (APMgLN) crystals. The APMgLN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMgLN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal work- ing conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 p_J and 700 ~J are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMgLN crystal is optimized according to this pump condition. To the best of our knowledge, this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMgLN crystals.
基金supported by the Open Research Fund of State Key Laboratory of Pulsed Power Laser TechnologyChina(No.SKL2017KF04)。
文摘We report on a new scheme for efficient continuous-wave(CW)mid-infrared generation using difference frequency generation(DFG)inside a periodically poled lithium niobate(PPLN)-based optical parametric oscillator(OPO).The pump sources were two CW fiber lasers fixed at 1018 nm and 1080 nm.One worked as the assisted laser to build parametric oscillation and generate an oscillating signal beam while the other worked at low power(3 W)to induce DFG between it and the signal beam.The PPLN temperature was appropriately adjusted to enable OPO and DFG to synchronously meet phase-matching conditions.Finally,both low-power 1018 nm and 1080 nm pump beams were successfully converted to 3.1μm and 3.7μm idler beams,respectively.The conversion efficiencies of the 1018 nm and 1080 nm pumped DFG reached 20% and 15%,respectively,while their slope efficiencies reached 19.6% and 15%.All these data were comparable to the OPOs pumped by themselves and never realized before in traditional CW DFG schemes.The results reveal that high-efficiency frequency down-conversion can be achieved with a low-power nearinfrared pump source.
基金Japan Science and Technology Agency(JST)Japan Agency for Medical Research and Development(AMED)
文摘We demonstrated stable midinfrared(MIR) optical frequency comb at the 3.0 μm region with difference frequency generation pumped by a high power, Er-doped, ultrashort pulse fiber laser system. A soliton mode-locked161 MHz high repetition rate fiber laser using a single wall carbon nanotube was fabricated. The output pulse was amplified in an Er-doped single mode fiber amplifier, and a 1.1–2.2 μm wideband supercontinuum(SC) with an average power of 205 m W was generated in highly nonlinear fiber. The spectrogram of the generated SC was examined both experimentally and numerically. The generated SC was focused into a nonlinear crystal, and stable generation of MIR comb around the 3 μm wavelength region was realized.
基金National Natural Science Foundation of China(NSFC)(11547187,11405073,61405073)Shandong Provincial Key R&D Program(2017CXGC0416)
文摘Graphene-based surface plasmon waveguides(SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation(DFG) under near-infrared pumps.The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs∕Al Oxstructure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs∕Al Ox waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.
基金supported by the U.S. National Science Foundation
文摘The progress achieved on power scaling and compact and portable THz sources is reviewed.By reversely stacking the GaP plates,the photon conversion efficiency is improved from 25% to 40% which corresponds to the maximum value.When the number of the plates is increased from four to five,the output power decreases because of back conversion.The THz generation is also investigated by mixing the two frequencies generated by a single Nd:YLF solid-state laser.The average output power reaches 1 μW.The introduction of two Nd:YLF crystals significantly improves the output power to 4.5 μW.This configuration facilitates the generation of different output frequencies.
基金supported by the National Key R&D Program of China(No.2016YFA0301402)the National Natural Science Foundation of China(Nos.11474190,61601270,11654002,and 61775127)+1 种基金the Program for Sanjin Scholars of Shanxi Provincethe Fund for Shanxi "1331" Project Key Subjects Construction
文摘The intensity difference squeezed state, which means that the fluctuation of the intensity difference between signal and idler beams is less than that of the corresponding shot noise level(SNL), plays an important role in high sensitivity measurement, quantum imaging, and quantum random numbers generation. When an optical parametric oscillator consisting of a type-Ⅱ phase-matching periodically poled KTiOPO4 crystal operates above the threshold, an intensity difference squeezed state at a telecommunication wavelength can be obtained. The squeezing of 7.7 ± 0.5 dB below the SNL is achieved in an analysis frequency region of 2.4–5.0 MHz.
基金National Natural Science Foundation of China(NSFC)(61505236)Key Laboratory Foundation of Chinese Academy of Sciences(CAS)(CXJJ-15S099,CXJJ-17S026)Innovation Foundation of Shanghai Institute of Technical Physics(CX-54)
文摘We report the investigation on the performance of an amplification assisted difference frequency generation(AA-DFG) system driven by pulsed pump and continuous-wave primary signal lasers. A monolithic tandem lithium niobate superlattice was employed as the nonlinear crystal with a uniform grating section for the DFG process, followed by a chirp section for the optical parametric amplification process. The impacts of pump pulse shape, primary signal power, input beam diameter, and crystal structure on the pump-to-idler conversion efficiency of the AA-DFG system were comprehensively studied by numerically solving the coupled wave equations. It is concluded that square pump pulse and high primary signal power are beneficial to high pump-to-idler conversion efficiency. In addition, tighter input beam focus and smaller DFG length proportion could redeem the reduction in conversion efficiency resulting from wider acceptance bandwidths for the input lasers. We believe that such systems combining the merits of high stability inherited from cavity-free configuration and high efficiency attributed from the cascaded nonlinear conversion should be of great interest to a wide community,especially when the pulse shaping technique is incorporated.
基金supported by the Scientific Research Project of Liaoning Province Education Department (2020LJC16),China。
文摘Rheumatoid arthritis is a chronic,systemic autoimmune disease predominantly based on joint lesions with an extremely high disability and deformity rate.Several drugs have been used for the treatment of rheumatoid arthritis,but their use is limited by suboptimal bioavailability,serious adverse effects,and nonnegligible first-pass effects.In contrast,transdermal drug delivery systems(TDDSs)can avoid these drawbacks and improve patient compliance,making them a promising option for the treatment of rheumatoid arthritis(RA).Of course,TDDSs also face unique challenges,as the physiological barrier of the skin makes drug delivery somewhat limited.To overcome this barrier and maximize drug delivery efficiency,TDDSs have evolved in terms of the principle of transdermal facilitation and transdermal facilitation technology,and different generations of TDDSs have been derived,which have significantly improved transdermal efficiency and even achieved individualized controlled drug delivery.In this review,we summarize the different generations of transdermal drug delivery systems,the corresponding transdermal strategies,and their applications in the treatment of RA.
基金supported by the National Basic Research Program of China(Grant No.2014CB339802)the National Natural Science Foundation of China(Grant Nos.61675146,61471257,61505089,61275102&61271066)
文摘High-power terahertz(THz) generation in the frequency range of 0.1-10 THz has been a fast-developing research area ever since the beginning of the THz boom two decades ago, enabling new technological breakthroughs in spectroscopy, communication, imaging,etc. By using optical(laser) pumping methods with near-or mid-infrared(IR) lasers, flexible and practical THz sources covering the whole THz range can be realized to overcome the shortage of electronic THz sources and now they are playing important roles in THz science and technology. This paper overviews various optically pumped THz sources, including femtosecond laser based ultrafast broadband THz generation, monochromatic widely tunable THz generation, single-mode on-chip THz source from photomixing, and the traditional powerful THz gas lasers. Full descriptions from basic principles to the latest progress are presented and their advantages and disadvantages are discussed as well. It is expected that this review gives a comprehensive reference to researchers in this area and additionally helps newcomers to quickly gain understanding of optically pumped THz sources.
基金supported by the Foundation for Polish Science within the First TEAM program co-financed by the European Union under the European Regional Development Fund (No.First TEAM/2017-4/39)the Knut and Alice Wallenberg Foundation (No.KAW 2015.0159)。
文摘A 125 MHz fiber-based frequency comb source in the mid-infrared wavelength region is presented. The source is based on difference frequency generation from a polarization-maintaining Er-doped fiber pump laser and covers a spectrum between2900 cm^(-1) and 3400 cm^(-1) with a simultaneous bandwidth of 170 cm^(-1) and an average output power up to 70 m W. The source is equipped with actuators and active feedback loops, ensuring long-term stability of the repetition rate, output power, and spectral envelope. An absorption spectrum of ethane and methane was measured using a Fourier transform spectrometer to verify the applicability of the mid-infrared comb to multispecies detection. The robustness and good long-and short-term stability of the source make it suitable for optical frequency comb spectroscopy of hydrocarbons.
基金supported by the National Natural Science Foundation of China(Nos.21673025,11974091,21203042,11574062)the Open Projects of Key Laboratory of Polyoxometalate Science of Ministry of Education(NENU)of China and the State Key Laboratory of Supramolecular Structure and Materials(JLU)of China(No.SKLSSM2021020).
文摘In this work,azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical(NLO)properties.The sum-over-states(SOS)model based calculations demonstrate that dipolar contributions are larger than octupolar contributions to the static first hyperpolarizability(〈β0〉)in most nano-graphenes except those with high symmetry(e.g.,a C2v nano-graphene has octupolar contributionsΦJ=3 up to 59.0%of the〈β0〉).Nano-graphenes containing two parallel orientating azulenes(i.e.,Out-P and Out-Ps)have large dipole moments,while their ground state is triplet.Introducing B/N/BN atoms into the positions with a high spin density transfers the ground state of Out-P and Out-Ps to closed-shell singlet,and the Out-Ps-2N has a large〈β0〉of 1621.67×10−30 esu.Further addition of an electron donor(NH2)at the pentagon end enhances the〈β0〉to 1906.22×10−30 esu.The two-dimensional second-order NLO spectra predicted by using the SOS model find strong sum frequency generations and difference frequency generations,especially in the near-infrared and visible regions.The strategies to stabilize the electronic structure and improve the NLO properties of azulene-defect carbon nanomaterials are proposed,and those strategies to engineer nano-graphenes to be semiconducting while maintaining theπ-framework are exten-dable to other similar systems.