Zhang Jia-Sen

Ultrahigh spatiotemporal resolved spectroscopy

We review the technique and research of the ultrahigh spatiotemporal resolved spectroscopy and its applications in the field of the ultrafast dynamics of mesoscopic systems and nanomaterials. Combining femtosecond time-resolved spectroscopy and scanning near-field optical microscopy (SNOM), we can obtain the spectra with ultrahigh temporal and spatial resolutions simultaneously. Some problems in doing so are discussed. Then we show the important applications of the ultrahigh spatiotemporal resolved spectroscopy with a few typical examples.

Complex Modulation in Plasmon-Assisted Transmission Spectra of a Two-Slit Structure

We study the plasmon-assisted transmission of two kinds of slit structures in a 290-nm-thick silver film on a glass substrate. For the two-slit structure, the total transmission intensity spectra displays a complex modulation, which is attributed to different propagation constants of the surface plasmon polaritons (SPPs) on the silver-air and silver-glass interfaces. Replacing one of the two slits by a shallow corrugation results in a simple sinusoidal intensity modulation because of the only effective SPP excitation and propagation on the silver-air interface. These confirm the role of different SPP propagations and interference in the transmission properties of metal nanoslits.

Crosstalk Noise Reduction in Shift-Multiplexed Holographic Storage System Using Multiple Point Sources

We propose and analyse a new method to reduce cross-talk noise in a shift multiplexed holographic storage system using multiple point sources. The normalized diffraction efficiency is given analytically with respect to the shift distance. The noise-to-signal ratio is defined and calculated to value the cross-talk of the system. The numerical results show that using multiple point sources can effectively decrease the cross-talk.

All-Optical Modulation with a Surface Plasmon Mach-Zehnder Interferometer

We use two parallel nano-slits in a silver film to form a surface plasmon Mach–Zehnder interferometer (MZI), based on the interference of two surface plasmon waves propagating along the two surfaces of the silver film. Coating the silver film with a photoinduced birefringence polymer film, we achieve optical modulation of the MZI output by changing the refractive index of the polymer film with a pump beam. An on/off ratio of 2.7 is obtained for a probe wavelength of 865 nm.

Resolution of a photorefractive incoherent-to-coherent optical converter

In this paper, we calculate the resolution of a photorefractive incoherent-to-coherent optical converter on the image plane for small diffraction efficiency by taking into account the optical imaging characteristics of the imaging lens. For a thin grating, we obtain a high resolution, which is comparable with the experimental results.

Femtosecond Laser Pumped Conical Emission and Seeded Ring Amplification in BBO Crystals

The characteristics of femtosecond laser pumped conical emission in quadratic media of β-barium borate (BBO) crystals are analysed. A minimized dispersion phase-matching angle, by which a wide-range spectrum can be obtained, is used for broadband amplification. When a seed of a chirped supercontinuum pulse is input, it is found that the seed in wavelength 500 nm–750 nm is amplified and time resolved.

Triple Encrypted Holographic Storage and Digital Holographic System

We propose a triple encrypted holographic memory containing a digital holographic system. The original image is encrypted using double random phase encryption and stored in a LiNbO3:Fe crystal with shift-multiplexing. Both the reference beams of the memory and the digital holographic system are random phase encoded. We theoretically and experimentally demonstrate the encryption and decryption of multiple images and the results show high quality and good fault tolerance. The total key length of this system is larger than 4.7 × 1033.

Influence of the probe–sample interaction on scanning near-field optical microscopic images in the far field

We have studied the influence of probe–sample interaction in a scanning near-field optical microscopy (SNOM) in the far field by using samples with a step structure. For a sample with a step height of ~λ/4, the SNOM image contrast between the two sides of the step changes periodically at different scan heights. For a step height of ~λ/2, the image contrast remains approximately the same. The probe–sample interaction determines the SNOM image contrast here. The influence of different refractive indices of the sample has been also analysed by using a simple theoretical model.

Contrast Reversal of Topography Artifacts in a Transmission SNOM

We demonstrate the contrast reversal behaviour of topography artifacts by changing the diameter of the collection diaphragm in a transmission scanning near-field optical microscopy (SNOM). This originates from the change of the approach curves. Such contrast reversal phenomenon is used to distinguish the artifact signal from the true optical signal of the SNOM image. We also show that continuously changing the diaphragm to a proper diameter can greatly reduce topography artifacts.