White-light Michelson Interferometer Research Articles

Measurements of refractive indices and thermo-optical coefficients using a white-light Michelson interferometer.

A dispersive white-light Michelson interferometer was used to determine the wavelength dependence of the refractive index (n) in the visible range from 425 to 775 nm and the thermo-optical coefficient (dn/dT) of fused silica (FS) and borosilicate glass (BK7). For FS, the values obtained for n and dn/dT at 546 nm were 1.46079 and 11.3×10-6 K-1, respectively, while the values for BK7 glass were 1.51825 and 2.2×10-6 K-1, respectively, which is in good agreement with the literature. The accuracy of the methodology used for n was almost 10-6, enabling precise spectroscopic characterization of materials across a wide spectral range.

Group velocity dispersion of CdSSe/ZnS core–shell colloidal quantum dots measured with white light interferometry

We measure the group velocity dispersion coefficient of CdSSe/ZnS core–shell colloidal quantum dots in liquid suspension in the ∼700–900nm wavelength range using a white-light Michelson interferometer. Two different sizes of dots are investigated. In both cases, the group velocity dispersion coefficient decreases with increasing wavelength above the absorption edge in the dots. For quantum dots in which the linear absorption spectrum shows clear peaks, the absorption characteristics of the dots can be used to accurately model the wavelength-dependence of the group velocity dispersion coefficient.

White-light interferometers with polarizing optics for length measurements with an applicable zero-point detection

For absolute length and form measurements at a large working distance (>150 mm) two special interferometers, a tandem interferometer and a Michelson interferometer with achromatic polarizing optics are constructed. In our experiments, both consist of a combination of one low-coherence interferometer and one laser interferometer. For the low-coherence interferometer part, a simple white-light source with less than 100 µW optical power output is chosen. It bases upon a low-cost fiber-coupled near-infrared LED with a large spectral width (FWHM > 68 nm at 825 nm). The use of achromatic polarizing optics such as broadband polarizing beamsplitters and achromatic quarter-wave plates in the low-coherence interferometer parts increases the contrast level of the white-light signal fringe pattern to nearly 100%. Furthermore, the fringe pattern in a polarized interferometer has no subsignatures and is unique. Hence, different algorithms are tested for signal processing and automated zero-point detection of the white-light signature. The software for an automated measurement is tested in a standard room without thermal control and without damped oscillation. Therefore, in experiments with the tandem interferometer, it was possible to measure the zero-point position of a white-light signature with a peak-to-peak difference of 154 nm under uncontrolled environmental conditions without thermal stabilization. The white-light Michelson interferometer with polarizing achromatic optics allows zero-point detections with a standard deviation (mean value) of less than 15 nm. The drift is proved through measurement results.

Ultrabroadband infrared chirped mirrors characterized by a white-light Michelson interferometer

We fabricated and characterized a pair of ultrabroadband chirped mirrors (CMs) in the infrared. These mirrors provide smooth control of the spectral phases in the wavelength range 1200–2200 nm, nearly one octave of a bandwidth. A scanning-type white-light Michelson interferometer was developed to measure spectral dispersion. We confirmed that the dispersion of the CMs well reproduced the designed dispersion. Furthermore, the CMs’ damage threshold was measured to be $${>}390\,\hbox {mJ}/\hbox {cm}^2$$ for 10-fs pulses, which corresponds to $${>}37\,\hbox {TW}/\hbox {cm}^2$$ .

Reduction of chromatic aberration influences in vertical scanning white-light interferometry

Vertical scanning white-light interferometry (SWLI) is a well-established method that is widely used in high precision surface topography measurement. However, SWLI results show characteristic slope-dependent errors due to dispersion effects and lateral chromatic aberrations of the optical imaging system. In this paper, we present methods to characterize these systematic errors related to dispersion and lateral colour. Lateral colour leads to field-dependent systematic discrepancies of the topography data obtained from the envelope position of a low-coherence interference signal and the data resulting from its interference phase. Hence, an erroneous fringe order obtained from the envelope position leads to a 2π phase jump and thus to a so-called ghost step in the measured topography. Our first approach to solve this problem is based on the measurement of a surface standard of well-known geometry. By comparison of measurement results related to the envelope position and the phase of SWLI signals, the systematic error is estimated and a numerical error compensation method is proposed. Both experimental and simulation results confirm the validity of this numerical method. In addition, using an improved design of a white-light Michelson interferometer we demonstrate experimentally that lateral chromatic aberrations and dispersion influences can be reduced also in a physical way. In this context, a conventional long working distance microscope objective is used which was not originally designed for a Michelson interference microscope.

Group velocity dispersion of dyes in solution measured with white-light interferometry

The group velocity dispersion (GVD) coefficient of four different dyes in solution is measured as a function of wavelength and concentration using a white-light Michelson interferometer. We find that the wavelength dependence of the GVD can be considerably different at wavelengths above and below the absorption resonance in a dye. Above the absorption resonance, the dye molecules can make a strong, wavelength-dependent contribution to the GVD of the solution. Below the absorption resonance, the dye molecules tend to contribute negligibly to the GVD of the solution. We find that the contribution of the dye molecules to the GVD can be modeled quite accurately using a simple Lorentz model with parameters set using the measured linear absorption properties of the dye.

Effect of input spectrum on the spectral switch characteristics in a white-light Michelson interferometer

We report here a detailed experimental study to demonstrate the effect of source spectral characteristics such as spectral bandwidth (Deltalambda), peak wavelength (lambda(0)), and shape of the spectrum on the spectral shifts and spectral switches measured due to temporal correlation in a white-light Michelson interferometer operated in the spectral domain. Behavior of the spectral switch characteristics such as the switch position, switch amplitude, and switch symmetry are discussed in detail as a function of optical path difference between the interfering beams. The experimental results are compared with numerical calculations carried out using interference law in the spectral domain with modified source spectral characteristics. On the basis of our results we feel that our study is of critical importance in the selection of source spectral characteristics to further improve the longitudinal resolution or the measurement sensitivity in spectral-domain optical coherence tomography and microscopy.

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.

Full-field quantitative phase imaging by white-light interferometry with active phase stabilization and its application to biological samples

We report a Koehler-illumination-based full-field, actively stabilized, low-coherence phase-shifting interferometer, which is built on a white-light Michelson interferometer. By using a phase-stepping technique we can obtain full-field phase images of the sample. An actively stabilized phase-lock circuit is employed in the system to reduce phase noise. An application to human epithelial cells (HeLa cells) is achieved in our experiment. The advancement of this technique rests in its ability to take images of unstained biological samples quantitatively and on a nanometer scale.

Development of Ultrabroadband Light Source Based on Stimulated Raman Scattering in P-doped Silica Optical Fiber for Optical Coherence Tomography

We describe the operational characteristics of an ultrabroadband light source using a fiber Raman laser based on the stimulated Raman scattering in a single-mode optical fiber pumped by a self Q-switched Ti:sapphire laser for application in optical coherence tomography. Ultrabroadband output light covering the range from 770 to 1650 nm was obtained using a 500-m-long single-mode P-doped SiO2 optical fiber pumped by the Ti:sapphire laser with a spectral width of 13 nm. When a white-light Michelson interferometer was constructed using the fiber Raman laser as a light source, a longitudinal spatial resolution of 1.7 µm was achieved.

Generation of Spectrally Continuum Light by Stimulated Raman Scattering in Optical Fiber

The operational characteristics of an ultra-broadband light source using the stimulated Raman scattering in a single-mode optical fiber for the application to optical coherence tomography is described. The ultra-broadband output light covering from 770 nm to 1650 nm was obtained using a 500-m-long single-mode phosphorus-doped Si02 optical fiber pumped by a self Q-switched Ti: sapphire laser with a spectral width of 13 nm. When a white-light Michelson interferometer was constructed using the fiber Raman laser as a light source, a longitudinal spatial resolution of 1.7 μm was achieved.

Broadband Light Source Based on Stimulated Raman Scattering in Silica Optical Fiber for Optical Coherence Tomography

A spatially coherent and temporally incoherent light source has been developed by stimulated Raman scattering in a single-mode optical fiber pumped by a conventional nano second solid-state laser. A broadband light with a bandwidth of roughly 400 nm was obtained using a 500-m-long single-mode SiO2 optical fiber at a pump energy of 0.6 mJ. When a white-light Michelson interferometer was constructed using the fiber Raman light source, the longitudinal spatial resolution of 1.8 µm was achieved.

Design of an interferometric system for the measurement of phasing errors in segmented mirrors.

One of the new problems that has to be solved for segmented mirrors is related to periodic phasing, because for such mirrors to exhibit diffraction-limited performance the segments have to be positioned with an accuracy of a fraction of a wavelength. We describe the optical design of an instrument that measures the phasing errors (i.e., tip, tilt, and piston) between two segments under daylight conditions. Its design is based on a high-aperture white-light Michelson interferometer. It was developed at the Center for Sensors, Instruments and Systems Development (CD6) of the Technical University of Catalunya, Spain, and its final testing was carried out on the Gran Telescopio Canarias test workbench.

Fiber optic extensometer for concrete deformation measurements

A fiber optic extensometer based on a scanning white light Michelson interferometer is presented. The instrument employs a light emitting diode as the light source and a single mode fiber with predetermined gauge length as the extensometer sensor head. Light to and from the sensor head is transmitted through a single mode lead (i.e., in/out) fiber. The sensor performance is insensitive to the in/out fiber extensions. The fiber optic extensometer was applied to measure the compression and tension of concrete specimens. The measurement results compare well with that from a conventional extensometer.

Intrinsic single-mode fiber-optic pressure sensor

Development and calibration of a fiber-optic pressure single mode sensor are described. The sensor is based on the intrinsic properties of a communication grade single-mode optical fiber. A self-referencing double interferometer was used for interrogation of the signal. The sensing interferometer is based on a white light Michelson interferometer. The sensor was evaluated through measurement of high pressures applied to sand samples. Experimental results demonstrate the linearity of the system in the range 0 to 38.08 MPa with a resolution of 0.03 MPa.

Enhanced three-dimensional reconstruction of surfaces using multicolor gratings

Most optical topolography systems use a single-wavelength laser for projection, using a swept spot, a moving line, or a projected grating. In a typical projected grating system, the gratings are shifted and a series of images is used to recover the 3-D shape of the target. When the series of images is analyzed in the normal phase shift manner, the resulting 2-D phase map typically has phase unwrapping problems due to noise and Nyquist limits. Surfaces with large vertical discontinuities present a problem for phase unwrapping 3-D shape recovery. We look at simultaneously projecting multiple wavelengths onto a surface to help avoid problems in unwrapping the 2-D phase map. Multicolor projection and shape recovery are demonstrated with a white-light Michelson interferometer and with a two-color Mach-Zehnder interferometer. Using multiple wavelengths, it is unnecessary to rotate the interferometer mirror to change the grating pitch and some operations can be done in parallel, which reduces scanning time. Limitations and improvements in the current system are discussed.

Enhancement of Nonlinear Optical Effect in One-Dimensional Photonic Crystal Structures

We observed the photonic band structure of one-dimensional photonic crystals using a white-light Michelson interferometer. In one-dimensional photonic crystals with a structural defect, there is a localized mode where the field is localized around the position of the defect. If the defect is made of nonlinear optical material, the effective nonlinearity of the photonic crystal is largely enhanced by the enhanced light intensity at the defect. In a one-dimensional photonic crystal with a defect, we observed a large enhancement of degenerate four-wave mixing efficiency. Since the total thickness of the whole structure is only a few micrometers, it was successfully used to form an optical phase-conjugated image.

Constructive and Destructive Two-Pulse Excitation Investigated with a White-Light Michelson Interferometer

Linear propagation of two pulses through methanol solution of aluminum phthalocyanine chloride is investigated using a modified white-light Michelson interferometer. The observed coherence time of the white light is 6 fs, and the separation between the two-excitation pulses is set to about 10 fs. The excitation is dependent on the phase-relation between the two pulses. We have observed an enhancement of the excitation when the two pulses are in-phase and strong suppression of the excitation when the two pulses are out of phase by π.

A white-light Michelson interferometer in the visible and near infrared regions

A white-light Michelson interferometer in the visible and near infrared regions is described which can obtain the cross-correlation interferogram between the incident light and the transmitted light through samples or optical components. By comparing the autocorrelation interferogram of the incident white light with the cross-correlation interferogram between the incident light and the transmitted light, we can obtain linear response functions of samples or optical components with femtosecond time resolution. Fourier analysis of the interferograms gives also the complex optical constants of the samples without relying on the Kramers–Kronig relation.

Linear propagation of light investigated with a white-light Michelson interferometer

Linear propagation of light was investigated by using a white-light Michelson interferometer. This method gives the full information on the deformation of broadband optical pulses by the passage through samples in the linear regime. We observed the delay of pulse propagation for cobalt chloride in pyridine, free-induction decay signal for oxazine 1 in methanol, and the increase of peak velocity for nigrosine in water. By Fourier analysis of the interferograms, complex optical constants of the samples were also obtained.