Biomedical subjects

Liren Liu

Publications and source records attributed to Liren Liu.

7 recordsLinked to original sources

PubMed2004

Optimal switching from recording to fixing for high diffraction from a LiNbO3:Ce:Cu photorefractive nonvolatile hologram.

An oscillatory characteristic of diffraction is observed as a result of strong beam coupling in a weakly oxidized LiNbO3:Ce:Cu crystal during the recording step in the production of nonvolatile photorefractive holograms. On this basis the optimal switching time from the recording step to the fixing step for high diffraction of a fixed hologram is studied. It is shown that switching after the first diffraction maximum leads theoretically to fixed diffraction of as much as 100% with a suitable switching time. Both an experimental demonstration and a theoretical simulation are presented.

Journal Article↗

PubMed2003

Circular Dammann grating.

A circular Dammann grating that can produce circular equal intensities at various orders in the far field is described. A set of parameters such as order, circular number, uniformity, and diffraction efficiency has been defined to describe the novel diffractive phase elements. Numerical solutions of binary-phase (0, pi) circular Dammann gratings are given. The results of experiments with a four-order circular Dammann grating made by a lithographic technique are presented. This novel diffractive optical element should be highly interesting in a wide variety of practical applications.

Journal Article↗

PubMed2003

Multifunctional double-layered diffractive optical element.

We propose a novel multifunctional double-layered diffractive optical element (DOE) based on the fractional Talbot effect. This DOE consists of two layers: one is the encoding layer, in which multiple sub-DOEs, i.e., multiple optical functions, are encoded; the other is the decoding layer, which is a properly designed Talbot illuminator. This DOE can perform each of the multiple optical functions one by one by shifting the encoding layer. Experimental results demonstrate that this method is efficient. This device should be highly interesting for integrated optics, optical interconnection, secure optical storage, and dynamic optical fiber communications.

Journal Article↗

PubMed2003

Nearly-off-axis transmissivity of Solc birefringent filters.

The characteristics of light propagating near the axis of a birefringent filter are studied. A generalized formulation to describe the nearly-off-axis transmissivity of a Solc birefringent filter is derived. On this basis, the polarization conoscopic figures of Solc filters with different numbers of birefringent plates are simulated. Furthermore the variation of spectral transmission with angle of incidence is analyzed, and the field-of-view transmissivity and the spectral transmissivity averaged with respect to the spread of incident light are given. Primary experiments for verification are also demonstrated.

Journal Article↗

PubMed2003

Uniform theory of the Talbot effect with partially coherent light illumination.

A uniform formulation for the self-imaging of gratings with any kind of partially coherent illumination is developed in terms of the cross mutual spectral density of the partial coherence theory. The formulation includes the time diffractive intensity distribution and the averaged diffractive intensity distribution at self-imaging distances and can be applied to both continuous and temporal illuminations with any kind of spectra. It is found that the averaged intensity distribution is related only to the intensity spectrum of illumination. The continuous polychromatic illumination and the ultrashort laser pulses with or without frequency chirp are then studied by a numerical stimulation. It is shown that the ultrashort laser pulse and the continuous polychromatic illuminations have similar averaged self-image distributions. Thus the Talbot effect may help in the study of the temporal and spectral characteristics of ultrashort laser pulses. An experiment with an LED is given, as well.

Journal Article↗

PubMed2002

Nonvolatile holograms in LiNbO3:Fe:Cu by use of the bleaching effect.

We report our observation of a bleaching effect under an ultraviolet exposure in LiNbO3:Fe:Cu crystals. Two three-step recording-transferring-fixing schemes are proposed to record nonvolatile photorefractive holograms in such crystals. In the schemes two red laser beams and an ultraviolet illumination are used selectively to write the charge grating inthe shallow-level Fe centers, to develop the charge grating inthe deep-level Cu centers by transferring the charge grating in the Fe centers, and to fix only thecharge grating in the Cu centers for unerasable read-out. Experimental results, verifications, and an optimal recording scheme are given. A comparison of the lithium niobate crystals of the same double-doping system of Fe:Mn, Ce:Mn, Ce:Cu, and Fe:Cu is outlined.

Journal Article↗

PubMed2002

Large-aperture automatic focimeter for the measurement of optical power and other optical characteristics of ophthalmic lenses.

We propose an optical apparatus enabling the measurement of spherical power, cylindrical power, and optical center coordinates of ophthalmic lenses. The main advantage of this new focimeter is to provide a full bidimensional mapping of the characteristics of ophthalmic glasses. This is made possible thanks to the use of a large-area and high-resolution position-sensitive detector. We describe the measurement principle and present some typical mappings, particularly for progressive lenses. We then discuss the advantages in terms of speed and versatility of such a focimeter for the measurement of complex lens mappings.

Equipment Design↗