Biomedical subjects

Lijiang Zeng

Publications and source records attributed to Lijiang Zeng.

6 recordsLinked to original sources

PubMed2006

Method of making mosaic gratings by using a two-color heterodyne interferometer containing a reference grating.

We propose and demonstrate a two-color heterodyne interferometric method for making a perfect mosaic of two planar gratings that can substitute for a single and larger grating without introducing wavefront aberration at any wavelength. The lateral and longitudinal phase errors are separated and eliminated by use of two wavelengths in the interferometry. The accuracy of the phase difference measurement is improved by this heterodyne scheme. The method ensures that the lateral gap between the two subaperture gratings is an integer multiple of the grating period. For a pair of 0.72 microm period gratings we experimentally achieved a lateral alignment error of less than 1% of the grating period.

Journal Article↗

PubMed2005

Experimental verification of enhanced transmission through two-dimensionally corrugated metallic films without holes.

We present experimental results to verify extraordinary optical transmission through two-dimensionally periodic, corrugated metallic films without holes as predicted by Bonod et al. [Opt. Express 11, 482 (2003)]. We also experimentally confirmed that using symmetric structures (metallic films sandwiched between two identical dielectric media) is advantageous for boosting the coupling of surface plasmons so as to create strong transmission peaks.

Journal Article↗

PubMed2005

Two-dimensional surface profile imaging technique based on a double-grating frequency shifter.

A two-dimensional surface profile imaging technique that uses a low-coherence heterodyne interferometer is proposed. A double-grating frequency shifter was used in a tandem interferometer to provide the achromatic frequency shift for low-coherence light. A chopper, together with a processing circuit, was implemented to modulate the interference fringes. The surface profile was measured from the interference fringes taken by a CCD camera using a five-step method. The uncertainty in the displacement measurement is 0.34 microm for a displacement range of 43 microm. The surface profile of a glass sample with low effective reflectivity was acquired.

Algorithms↗

PubMed2005

Measurement of duty cycles of photoresist grating masks made on top of multilayer dielectric stacks.

We present a novel and nondestructive method for measuring the duty cycles (ratio of ridge width to period) of submicrometer rectangular photoresist gratings made on top of multilayer dielectric stacks. The method exploits the fact that the effective index of the leaky mode that has a strong evanescent tail in the cladding changes with the duty cycle of the grating situated at the interface between the top dielectric layer and the cladding. By comparing measured coupling angles of the leaky mode with a theoretical or experimentally calibrated relationship between coupling angles and duty cycle, one can determine the duty cycle of the grating. This method is applicable even when the grating period is less than the measurement wavelength. It is simple because it does not require any power measurement. Most importantly, it is virtually independent of groove depth. The physical principle of the method and the results of experimental verification are presented.

Journal Article↗

PubMed2004

Measurements and numerical analysis for femtosecond pulse deformations after propagation of hundreds of meters in air with water-vapor absorption lines.

We have clarified the influences of water-vapor absorption lines in air on femtosecond pulse propagations from experimental and theoretical points of view. Precise measurements for the femtosecond pulse shapes after propagation of as much as 300 m through air have been made in a semiunderground optical testing tunnel. We observed the pulse splitting and the enhancement of the pulse broadening due to the 100-m propagation in air. The experimental results are in good agreement with the theoretical analysis by use of the HITRAN database at the edge and the center of the water-vapor absorption regions in air. Measured autocorrelation traces are mostly reproduced by those calculated with only the real part (dispersion) of the refractive index modulated by water-vapor absorption lines in air. This fact enables us to conclude that the pulse deformations due to water absorption lines in air are caused mainly by the real part (dispersion), not by the imaginary part (absorption), of the refractive index of air.

Journal Article↗

PubMed2003

Measuring wing kinematics, flight trajectory and body attitude during forward flight and turning maneuvers in dragonflies.

A robust technique for determining the wing kinematics, body position and attitude of a free-flight dragonfly is described. The new method is based on a projected comb-fringe technique combined with the natural landmarks on a dragonfly, allowing us to establish the local body-centered coordinate system with high accuracy, and to measure the body attitude at any instant. The kinematic parameters, including wingbeat frequency, flapping angle, angle of attack, torsional angle and camber deformation, required no assumptions to be made with respect to wing geometry, deformability (except the assumption of rigid leading edges) or bilateral wing symmetry. Two typical flight behaviors, forward flight and turning maneuvers, of dragonflies Polycanthagyna melanictera Selys were measured and analyzed.

Animals↗