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According to the polarization characteristics of the thin film narrowband filter,the stack of narrowband filter used in oblique incidence is provided based on the genetic arithmetic in this paper.A 100GHz five-cavity thin film filter used in 18° incidence is optimized based on the programme.The stack can eliminate the phenomenon of polarization light central wavelength separation used in oblique incidence and it has low polarization dependent loss.It can be used as an angle-tuned thin film filter for wavelength modulation.Compared with the thin film filter stack obtained by needle arithmetic design,it has higher rectangle degree,larger wavelength tunable range and less polarization dependent loss.The experimental results show it meets the demand of design and its tunable range is more than 25 nm.

Spontaneous parametric down conversion of the femtosecond pulse with a type-I β-barium borate(BBO) crystal was studied experimentally,which induced to the generation of colored conical emission(CCE).The influence of parametrics on the conversion efficiency and the characteristics of CCE was discussed in detail.Experimental results show that the green conical emission has the biggest divergence angle,which is consistent with the calculation results based on the phase matching condition.When the pumped beam is incident on-axis,the intensity of the CCE will become stronger with the increase of the pump intensity and the thickness of crysta,and the center wavelength of the biggest diverging angle conical emission will change toward long wave.CCE and super-continuum emission can also be observed with different polarization directions.

Based on the multi-beam interference principle,a transmitting intensity expression of a Gaussian beam incidenting obliquely on an angle-tuned narrowband filter is derived.According to the result,the influence of the incidence angle on the transmission of a Gaussion beam is investigated theoretically.The calculation and experiment results show that the size of the transmitting beam spot is brodened obviously in oblique incidence.When the incident angle of the thin-film filter is relatively small,the position of the peak of the transmitting beam is shifted and the beam is not in Gaussian distribution.When the incident angle of the filter is relatively large,the transmitting beam consists of a series of space-separated beams.