Wavefront aberration of human eye is an important foundation for customized vision correction. In most current
aberrometers, near infrared light is used to measure ocular wavefront aberration, whereas for customized visual correction,
wavefront aberration data in visible range are required. With the measured wavefront aberration, corneal topography and
eye's axial lengths data, individual eye models for twenty normal human eyes are constructed with the optical design
software ZEMAX. Changing the incidence light wavelength and the refractive indexes of eye models, the values of
defocus, astigmatism, higher-order aberrations in the measuring wavelength (833nm) and at the most sensitive wavelength
of human eye (555nm) are obtained. Average focus shift between 833nm and 555nm is found to be about 0.94D, and
different slightly for different individuals; the differences of astigmatism and higher-order aberrations between 833nm and
555nm are quite slight. For customized visual correction, the measured defocus value should be modified, whereas the
measured astigmatism and higher-order aberrations could be used directly for the current correction precision. Individual
eye model is a useful tool for accurate transformation of the measured wavefront aberration data into the data for visible
spectrum.
The differences of nonlinear absorption coefficient β are theoretically and numerically studied under both of the beam sections of plain and Gaussian distribution. The formula of energy transmission is derived on the base of temporal profile of Gaussian pulse beam. According to the formula, the absolute and relative
differences of β are also estimated in compare with plain beam and the pulse beam that is rectangular in time
but Gaussian in space. The relative differences turn out theoretically to be about 183% and 41.4% respectively.
The further numerical simulation shows that these values are only the least differences. The existed differences mean that, according to the temporal influence of pulse, one should get a lager value of β in past performed routine experiments of nonlinear energy transmission. Our result suggests that, by taking temporal profile of a pulse beam into account, one can obtain more exact value of two-photon absorption cross section of the molecule experimentally.
In the present study, the propagation characteristics of terahertz radiation in both metallic film-coated and dielectric
film-coated hollow waveguides have been theoretically analyzed. The dominant modes in metallic film-coated and
metal/dielectric film-coated hollow waveguides are respectively TE11 and HE11 modes. Theoretical attenuation
coefficients of terahertz radiations in hollow waveguides with a bore diameter of 1mm film-coated with Au, Pb and Ni at
different incident frequencies are compared. The dominant mode, i.e. TE11 mode, as a function of bore diameter in
hollow waveguides film-coated with different metals are calculated at a given incident frequency. An additional
dielectric film with appropriate thickness on the metal films can effectively enhance the wave reflection, resulting in
decreased attenuation of the terahertz radiation propagating in hollow waveguides. Calculated results indicate that the
attenuation of the terahertz radiation in metal/dielectric film-coated hollow waveguide with a bore diameter of 1mm for a
given incident wavelength of 200μm is about 4 times lower than that in metal hollow waveguide with the same bore diameter.
Based on the analytical solutions of the wave equations in the elliptical-cylindrical coordinate system, the propagation
characteristics of hollow elliptical waveguide for THz Radiation are investigated, and then the mode characteristic
equations are also given. Our results show that the mode characteristic equations of a circular waveguide can be treated
as a special case of an elliptic waveguide. The propagation characteristics are numerically simulated depending on the
refractive index of dielectrics films and the eccentricity of the elliptic waveguide. The cutoff wavelengths of guided
modes in the elliptic waveguide are also presented.
A new self-mixing interference structure with compensatory cavity is proposed. The model of this structure is also established. With compensatory cavity, the defects of self-mixing interference signals, such as phase and environmental disturbance, can be improved. In addition, the range of distance measuring can be extended.
Self-mixing interference effects in the LD pumped green laser under the threshold current are observed. The behaviors of laser under the threshold current are more like LED. Based on this, we put forward for the first time the idea that replacing the light source with LED. If so, the lifetime and price of this kind of interferometer, and also the cubage of the interferometer is reduced. The accurate threshold current of lasers can also be measured using this equipment. This will be great contribution to self-mixing interference effects and its applications.
Self-mixing interference effects in the LD pumped green laser are observed. Then small disturbance theory is used for the first time to analysis the quantum behaviors in the laser. The cavity system without feedback is considered to be the initial status function, the influence of feedback is considered to be the disturbance. The interaction Hamilton is deduced finally.
Self-mixing interference (SMI) effects have been widely used in measuring the distance and displacement and velocity. Conventional methods are fringe counting and phase analysis. The former method has a precision of λ/10 in a multi-mode LD pumped solid-state laser (LDPSSL), while the latter has a precision of nearly λ/50 concerning the multiple reflections. Theoretical analysis and simulation calculations are presented.
It's unavoidable that there is a deviation (called grating period deviation in this paper) between the real QPM period of periodically poled crystal and the ideal value to cause phase mismatching. By tuning temperature, we can get phase matching again. We present the formula of the relation between temperature tuning value ΔT and grating period deviation ΔΛ of periodically poled crystal for SHG in order to get phase matching. Our numerical analyses show that ΔT of PPLN-SHG is approximately directly proportional to the ΔΛ, and when the pumping wavelength or the quasi-phase matching order increase, the slope of (formula available in paper)to approximately ΔΛ curve will go down.
A solid-state laser source with flat-top wide beam profile was designed and made. The laser source was mainly made up of an Nd:YAG solid-state laser at 1064 nm and a maximum 267 x collimating telescope. A 2 W laser diode (LD) pumped Nd:YAG laser with flat-concave cavity was adopted as the primary laser source at 1064 nm. Then the output laser (1064 nm) was injected into a collimating telescope. We designed three schemes according to spherical wave theory and chose the best one based on our experiments. We found out the spherical aberration (including axial and off-axial points) must be corrected. At last, an output laser beam with 80 mm diameter, 0.4 mrad divergence angle, > 50 mW output power, and ±10% intensity distribution of cross section, was obtained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.