Wavelength scanning interferometry using a Ti:Sapphire laser with wide tuning range

Improvement of the depth resolution in depth-resolved wavenumber-scanning interferometry using multiple uncorrelated wavenumber bands

“…Unfortunately, mode hopping exists in many laser sources, such as diode lasers, external-cavity diode lasers, Ti:sapphire lasers, etc. [2][3][4][5]. It is common in DRWSI that the depth resolution is limited by the mode hopping of the laser source.…”

“…Wide-field depth-resolved wavenumber-scanning interferometry (DRWSI) or swept-source optical coherence tomography (SSOCT) is a noninvasive 3D imaging technique, using wavenumber-scanning technology to detect the 3D structure and deformation field, etc., with the advantages of a large depthresolved range and stationary components [1][2][3][4][5]. The technology can be traced back to digital phaseshifting interferometry using a directly frequencymodulated diode laser in the 1980s, when phase shifting was found by altering the current to tune its wavelength [6].…”

“…The advantage is that this range of wavelength scanning makes the DRWSI have the finest depth resolution, at the expense of a relatively complex bulky optical system. Ruiz and Huntley et al provided a solution to employ a wide-field CCD camera and an external-cavity diode laser or a Ti:sapphire laser as the laser sources [2][3][4][5] in the DRWSI. The advantage is that it makes full use of the mature technology so as to improve its performance Due to its low cost, compact size, and multiple wavelength bands, the single-longitude-mode FabryPerot diode laser is a very promising application of DRWSI.…”

“…The only obstacle to prevent its further development is mode hopping in the output of these laser sources, which breaks the whole range of the wavelength or wavenumber scanning into uncorrelated narrow bands, and results in a poor depth resolution in the DRWSI. In 2012, Davila et al described a method to record the fringe patterns of multiple optical wedges to measure the wavenumbers on time with high resolution and immunity to the ambiguities caused by large wavenumber jumps [4,5]. Furthermore, in order to overcome the nonlinearity or the mode hops of the laser, the series of unequal-space sampling is linearly fitted for the Fourier transform (FT).…”

Quadrature wavelength scanning interferometry

“…Interferometers commonly used to measure surface topography are phase shifting [1,2], white light [2,3] and wavelength scanning [4,5]. Each type of interferometer has certain advantages and disadvantages concerning the acquisition of the fringe data and the extraction of surface topography data.…”