This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results...This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results indicate that, in the case of high-order dispersion, the walk-off effect takes on new characteristics and will influence considerably the shape, position and especially the number of the spectral regions of the gain spectra of modulation instability. Not only the group-velocity mismatch, but also the difference of the third-order dispersion of two optical waves will alter the gain spectra of modulation instability but in different ways. Depending on the values of the walk-off parameters, the number of the spectral regions may increase from two to at most four, and the spectral shape and position may change too.展开更多
To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,...To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness.By rotating the plate up to 35°along the beam direction,we reduced the walk-off angle up to ~ 13%.The same phenomenon is predicted by the model,confirming the performance of the model.It is found that,due to the walk-off effect,the intensity profile of the thirdharmonic generation beam is slightly degraded.To compensate for the observed phenomena and further reduce the walkoff,we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form.As a result,the walk-off is decreased to~ 48.81 mrad,providing ~ 30%relative reduction.By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction,the walk-off angle is further reduced to 38.9 mrad.Moreover,it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.展开更多
This work designs a four-platelet periodic multicrystal configuration in the second harmonic generation of ultra- short pulses as a new walk-off-compensating device. It theoretically investigates a proposed active and...This work designs a four-platelet periodic multicrystal configuration in the second harmonic generation of ultra- short pulses as a new walk-off-compensating device. It theoretically investigates a proposed active and a typical passive compensating scheme with the undepleted-pump approximation. The result shows that the angular and spectral band- widths are proportional to the number of crystal pairs as expected, but the temperature tunability is basically unaltered owing to inter-plate pulse interference. At the same time, an analysis reveals that a misuse of the phase mismatch factor is responsible for a historic controversy about pulse interference. A real design of an ultraviolet second harmonic generation （262.5 nm） is considered in a passive periodic [3-Barium Borate-calcite configuration, where the inter-plate pulse interference is found to form an azimuthal tuning restriction and to lower plate length tolerance. A subsequent numerical simulation with pump depletion is in good accordance with theoretical prediction.展开更多
We theoretically and experimentally investigate the wave front distortion in critically phase-matched continuouswave（CW） second harmonic generation（SHG）.Due to the walk-off effect in the nonlinear crystal,the gene...We theoretically and experimentally investigate the wave front distortion in critically phase-matched continuouswave（CW） second harmonic generation（SHG）.Due to the walk-off effect in the nonlinear crystal,the generated second harmonic is extremely elliptical and quite non-Gaussian,which causes a very low matching and coupling efficiency in experiment.Cylindrical lenses and walk-off compensating crystals are adopted to correct distorted wave fronts,and obtain a good TEM00 mode efficiently.Theoretically,we simulate the correction effect of 266-nm laser generated with SHG.The experiment results accord well with the theoretical simulation and an above 80% TEM_（00） component is obtained for 266-nm continuous-wave laser with a 4.8？-walk-off angle in beta barium borate（BBO） crystal.展开更多
Long-wave infrared （IR） generation based on type-Ⅱ （o→e＋o） phase matching ZnGeP2 （ZGP） and CdSe optical parametric oscillators （OPOs） pumped by a 2.05μm Tm,Ho：GdVO4 laser is reported. The comparisons of t...Long-wave infrared （IR） generation based on type-Ⅱ （o→e＋o） phase matching ZnGeP2 （ZGP） and CdSe optical parametric oscillators （OPOs） pumped by a 2.05μm Tm,Ho：GdVO4 laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency （PRF） with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9μm with a single crystal 28 mm in length.展开更多
基金Project supported by the Fundamental Application Research Project of the Department of Science ＆ Technology of Sichuan Province （Grant Nos 05JY029-084 and 04JY029-103）, the Key Program of Natural Science Foundation of Educational Commission of Sichuan Province （Grant No 2006A124）, and the Foundation of Science ＆ Technology Development of Chengdu University of Information Technology （Grant No KYTZ20060604）.
文摘This paper investigates the effects of walk-off among optical pulses on cross-phase modulation induced modulation instability in the normal dispersion region of an optical fibre with high-order dispersion. The results indicate that, in the case of high-order dispersion, the walk-off effect takes on new characteristics and will influence considerably the shape, position and especially the number of the spectral regions of the gain spectra of modulation instability. Not only the group-velocity mismatch, but also the difference of the third-order dispersion of two optical waves will alter the gain spectra of modulation instability but in different ways. Depending on the values of the walk-off parameters, the number of the spectral regions may increase from two to at most four, and the spectral shape and position may change too.
文摘To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type ⅡKTiOPO4 and type I β-BaB2O4 optical crystals,and the Gaussian output beam of a Q-switched Nd：YAG laser,a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness.By rotating the plate up to 35°along the beam direction,we reduced the walk-off angle up to ~ 13%.The same phenomenon is predicted by the model,confirming the performance of the model.It is found that,due to the walk-off effect,the intensity profile of the thirdharmonic generation beam is slightly degraded.To compensate for the observed phenomena and further reduce the walkoff,we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form.As a result,the walk-off is decreased to~ 48.81 mrad,providing ~ 30%relative reduction.By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction,the walk-off angle is further reduced to 38.9 mrad.Moreover,it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.
基金supported by the Tiptop-Talent Fund from Harbin University of Science and Technology
文摘This work designs a four-platelet periodic multicrystal configuration in the second harmonic generation of ultra- short pulses as a new walk-off-compensating device. It theoretically investigates a proposed active and a typical passive compensating scheme with the undepleted-pump approximation. The result shows that the angular and spectral band- widths are proportional to the number of crystal pairs as expected, but the temperature tunability is basically unaltered owing to inter-plate pulse interference. At the same time, an analysis reveals that a misuse of the phase mismatch factor is responsible for a historic controversy about pulse interference. A real design of an ultraviolet second harmonic generation （262.5 nm） is considered in a passive periodic [3-Barium Borate-calcite configuration, where the inter-plate pulse interference is found to form an azimuthal tuning restriction and to lower plate length tolerance. A subsequent numerical simulation with pump depletion is in good accordance with theoretical prediction.
基金Project supported by the National Natural Science Foundation of China(Grant No.91436103)Research Programme of National University of Defense Technology,China(Grant No.JC15-02-03)
文摘We theoretically and experimentally investigate the wave front distortion in critically phase-matched continuouswave（CW） second harmonic generation（SHG）.Due to the walk-off effect in the nonlinear crystal,the generated second harmonic is extremely elliptical and quite non-Gaussian,which causes a very low matching and coupling efficiency in experiment.Cylindrical lenses and walk-off compensating crystals are adopted to correct distorted wave fronts,and obtain a good TEM00 mode efficiently.Theoretically,we simulate the correction effect of 266-nm laser generated with SHG.The experiment results accord well with the theoretical simulation and an above 80% TEM_（00） component is obtained for 266-nm continuous-wave laser with a 4.8？-walk-off angle in beta barium borate（BBO） crystal.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60878011 and 61078008)the Program for New Century Excellent Talents in University,China (Grant No. NCET-10-0067)
文摘Long-wave infrared （IR） generation based on type-Ⅱ （o→e＋o） phase matching ZnGeP2 （ZGP） and CdSe optical parametric oscillators （OPOs） pumped by a 2.05μm Tm,Ho：GdVO4 laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency （PRF） with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9μm with a single crystal 28 mm in length.
