Experimental investigations of the scanning functions of galvanometer-based scanners with applications in OCT

We analyze the three most common profiles of scanning functions for galvanometer-based scanners (GSs): the sawtooth, triangular and sinusoidal functions. They are determined experimentally with regard to the scan parameters of the input signal (i.e., frequency and amplitude). We study the differences of the output function of the GS measured as the positional error of the oscillatory mirror from the ideal function given by the input signal of the device. The limits in achieving the different types of scanning functions in terms of duty cycle and linearity are determined experimentally for the possible range of scan parameters. Of particular importance are the preservation of an imposed duty cycle and profile for the sawtooth function, the quantification of the linearity for the sinusoidal function, and the effective duty cycle for the triangular, as well as for the other functions. The range of scan amplitudes for which the stability of the oscillatory regime of the galvo mirror is stable for different frequencies is also highlighted. While the use of the device in certain scanning regimes is studied, certain rules of thumb are deduced to make the best out of the galvoscanner. Finally, the three types of scanning functions are tested with a Fourier domain optical coherence tomography (FD OCT) setup and the conclusions of the study are demonstrated in an imaging application by correlating the determined limits of the scanning regimes with the requirements of OCT.     

Optical design of a dynamic focus catheter for high-resolution endoscopic optical coherence tomography

The optical system design of a dynamic focus endoscopic probe for optical coherence tomography is reported. The dynamic focus capability is based on a liquid lens technology that provides variable focus by changing its curvatures in response to an electric field variation. The effects of a cylindrical exit window present, in practice, for a catheter were accounted for. Degradation in image quality caused by this window was corrected to get diffraction limited imaging performance. As a result, the dynamically focusing catheter with a lateral resolution ranging from 4 to 6 mum through an approximately 5 mm imaging distance was designed without mechanically refocusing the system.     

Determination of the coherency matrix of a broadband stochastic electromagnetic light beam

The statistical ensemble of a fluctuating, statistically-stationary electromagnetic light beam is presented in terms of a 2 × 2 matrix, so-called coherency matrix. The method to determine such matrix for a quasi-monochromatic light beam has been proposed for many years. In this paper, we demonstrate that the method needs to be only slightly modified to determine the matrix elements of a broadband stochastic electromagnetic light beam, if one uses the representation of statistical wave fields in the space–frequency domain. The implementation of the method is demonstrated, and the coherency matrix measurement is validated using a well-defined elliptically polarized beam.     

Kinetic studies on styrene–divinylbenzene copolymerization by suspension technique

Kinetic studies on styrene and divinylbenzene (DVB) copolymerization by the suspension technique in a toluene diluent initiated by benzoyl peroxide are reported. Evaluation of the important reaction parameters is carried out. The crosslinked styrene–DVB copolymers can absorb toluene to a maximum swelling ratio of 17. The absorption/desorption took place instantaneously and reached the maximum value within 10 min, and it could be repeated many times, yet gave the consistent result. Rate equations evaluated by both integral and differential methods are investigated. High monomer orders of 1.5–2.3 were obtained. The activation energy for the polymerization was about 40 kcal/mol^?1. Autoacceleration was found even at low conversions. The acceleration was influenced by both monomer, crosslinker, and initiator concentrations. The integral and differential methods for the rate evaluation were compared, and the relationship between the rate equation and polymerization behavior was elucidated. The kinetic orders determined for this copolymerization show considerable deviation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1521–1540, 2001