The advantages of polarization imaging can be readily leveraged in remote sensing applications by applying subwavelength metal grating arrays in standard optical imaging systems.However,the efficient fabrication of th...The advantages of polarization imaging can be readily leveraged in remote sensing applications by applying subwavelength metal grating arrays in standard optical imaging systems.However,the efficient fabrication of these arrays remains a significant challenge due to their dual size-scale features,periodic subwavelength grating structures with feature sizes of hundreds of nanometers,and pixel quadrants with dimensions on the order of tens of micrometers.The present study addresses this issue by introducing contact-interference assembly hybrid lithography.With this method,fine grating structures are fabricated using the interference fringes generated by two coherent laser beams having a wavelength close to the feature size.By using a specially designed,flexible mask,the interference wavefront is then segmented to produce the grating structures in each quadrant of the array unit via a single-cycle process.Notably,sub-micron alignment accuracy is guaranteed by introducing an overlay measurement system.The adverse effects of the gap between the mask and the substrate are suppressed by a mechanism in which the refractive index is smoothed out.A fabrication platform was developed,and a double-layer metal grating with a 20 mm×20 mm four-quadrant array having a period of 950 nm and a unit size of 15μm×15μm was constructed using a total exposure time of 180 s.This represents a 3−4 orders of magnitude reduction in the fabrication time compared to that of electron beam lithography.The quadrant micro-polarizer was characterized,where the produced sample exhibited a polarization extinction ratio of over 20 dB and an equivalent transmittance of approximately 50%.The results reveal the feasibility of the proposed method for scalable fabrication.展开更多
We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced lase...We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced laser pulse train.Then, the laser pulse train illuminates the cathode to produce a frequency-chirped electron bunch train in a photocathode rf gun. Finally, the frequency-chirped electron bunch train passes through a tapered undulator to produce a quasi-single-cycle THz pulse. This experiment should allow comparison and confirmation of predictive models and scaling laws, and the preliminary experimental results will also be discussed.展开更多
文摘The advantages of polarization imaging can be readily leveraged in remote sensing applications by applying subwavelength metal grating arrays in standard optical imaging systems.However,the efficient fabrication of these arrays remains a significant challenge due to their dual size-scale features,periodic subwavelength grating structures with feature sizes of hundreds of nanometers,and pixel quadrants with dimensions on the order of tens of micrometers.The present study addresses this issue by introducing contact-interference assembly hybrid lithography.With this method,fine grating structures are fabricated using the interference fringes generated by two coherent laser beams having a wavelength close to the feature size.By using a specially designed,flexible mask,the interference wavefront is then segmented to produce the grating structures in each quadrant of the array unit via a single-cycle process.Notably,sub-micron alignment accuracy is guaranteed by introducing an overlay measurement system.The adverse effects of the gap between the mask and the substrate are suppressed by a mechanism in which the refractive index is smoothed out.A fabrication platform was developed,and a double-layer metal grating with a 20 mm×20 mm four-quadrant array having a period of 950 nm and a unit size of 15μm×15μm was constructed using a total exposure time of 180 s.This represents a 3−4 orders of magnitude reduction in the fabrication time compared to that of electron beam lithography.The quadrant micro-polarizer was characterized,where the produced sample exhibited a polarization extinction ratio of over 20 dB and an equivalent transmittance of approximately 50%.The results reveal the feasibility of the proposed method for scalable fabrication.
基金supported by the Major State Basic Research Development Program of China (grants no.2015CB859700)by the National Natural Science Foundation of China (grants no.11327902)Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning (no.SHDP201507)
文摘We propose a proof-of-principle experiment to test a new scheme to produce a single-cycle radiation pulse in free-electron lasers(FELs). Here, a few α-BBO crystals will be first used to produce an equally spaced laser pulse train.Then, the laser pulse train illuminates the cathode to produce a frequency-chirped electron bunch train in a photocathode rf gun. Finally, the frequency-chirped electron bunch train passes through a tapered undulator to produce a quasi-single-cycle THz pulse. This experiment should allow comparison and confirmation of predictive models and scaling laws, and the preliminary experimental results will also be discussed.
