Degradation of optical properties of a film-type single-wall carbon nanotubes saturable absorber (SWNT-SA) with an Er-doped all-fiber laser.

Single-wall carbon nanotubes (SWNTs) are promising materials for saturable absorbers (SAs) in mode-locked lasers. However it has been widely recognized that the degradation of optical properties of film-type SWNTs used in femtosecond mode-locked lasers limits the achievable long-term stability of such lasers. In this paper, we study the degradation of optical properties of SWNT-SA fabricated as sandwich type using HiPCO SWNTs with an Er-doped all-fiber laser. The thresholds of laser pump power are examined to avoid the damage of the SWNT-SA. Based on the proposed analysis, it is shown that all-fiber laser pulses of 300 fs pulse width, 3.85 mW average output power, 211.7 MW/cm² peak intensity and 69.9 MHz repetition rate can be reliably generated without any significant damage to the SWNT-SA film.

Separation algorithm for a 2D refractive index distribution and thickness profile of a phase object by laser diode-based multiwavelength interferometry.

A separation algorithm that uses three wavelengths for the simultaneous measurement of the two-dimensional refractive index distribution and thickness profile of transparent samples is proposed. The optical system is based on a Mach-Zehnder interferometer with laser diode-based multiwavelength sources. A liquid crystal retarder is used to obtain interference images at four states with phases, and the optical phase of the object is then calculated with a four-bucket algorithm. A glass rod and several samples, including a slide glass, a glass wafer, and a cover glass are used to obtain experimental results at wavelengths of 635, 660, and 675 nm. The refractive indices of the sample are distributed with an accuracy of less than 0.0003 and the thickness profile is calculated on the basis of the measured refractive index. This result demonstrates that the proposed algorithm can be used to separate the refractive index distribution and thickness profile of samples in two dimensions.

Simultaneous measurement method of total and self-interference for the volumetric thickness-profilometer.

A simultaneous measurement method for the total interference and self-interference of a sample is proposed. The proposed method is capable of making separate measurements of the thickness and surface profile of micro-patterned thin film. The system is an extension of a full-field wavelength scanning interferometer with a single acousto-optic tunable filter (AOTF) as a spectral imaging device. Separate measurements are realized via the polarization-sensitive diffraction of non-collinear acousto-optic interaction. That is, the diffraction angle of an AOTF is separated into different directions depending on the polarization state of the incident light. In so doing, the polarization states of a reference and a sample light were manipulated differently so that a single AOTF can generate the total interference and the self-interference signal in different directions simultaneously. Thus, a compact and light-efficient system is realized with an AOTF, a beam splitter and two CCDs. Thus, a compact system with light-efficiency of two to four times higher than the previously reported system is realized with an AOTF, a beam splitter and two CCDs. Details of the calibration procedures such as wavelength-frequency relation, image shift and registration between two CCDs are provided for the proposed setup. Experimental results are provided and compared to those using commercial equipment that demonstrate the efficiency of the proposed system for the high-speed measurements of the thickness and the surface profile of micro-patterned thin film.

Design of a prism to compensate the image-shifting error of the Acousto-Optic tunable filter.

The Acousto-Optic Tunable Filter (AOTF) is a high-speed full-field monochromator which generates two spectrally filtered light beams with ordinary and extraordinary polarization state. The AOTF is widely used to build full-field spectral imaging systems or a spectral domain interferometer. The angle of diffracted light in the AOTF changes according to the scanning of wavelength, which causes an image shift on the CCD plane. An analytic design of a prism system to compensate for the image shift is proposed in this paper. Analysis of light paths in a prism and experimental results verified a proposed compensation method. Experimental results agreed with simulation results based on the suggested prism model. Image shifting errors of ordinary and extraordinary rays were simultaneously minimized at optimal conditions with the designed prism.