Dual-wavelength digital holography with a single low-coherence light source

Abstract

We propose a measurement system using dual-wavelength digital holography and low-coherence interferometry to measure micro- and nanostructure surface heights. To achieve an extended axial step-measurement range and better image quality, a single light-emitting diode generates two distinct light sources by filtering different center wavelengths and narrower bandwidths. The system can measure surface profile with higher step heights and lower speckle noise in a large field-of-view. Using single-source lighting and a simple configuration, the method supports compactly configured and lower-cost surface-topography measurement systems applicable in various fields. Experimental results for a standard step sample verify the system's performance.

Quantitative imaging of the complexity in liquid bubbles’ evolution reveals the dynamics of film retraction

“…Herein, we used aqueous solutions that were sufficiently homogenous to not require any particular adjustment of the optical setup. However, when this is not the case and particularly inhomogeneous samples are to be studied, the use of two or more beams with different wavelengths is suggested 44 . Using different illuminating wavelengths with closer values gives us the possibility of creating a synthetic wavelength with a large value, and therefore we can enlarge continuous phase regions of the reconstructed wavefront.…”

Endowing a plain fluidic chip with micro-optics: a holographic microscope slide

“…The ideal solution, however, would be replacing the coherent laser source with LEDs. Lately, various groups have proposed configurations to achieve off-axis DH microscopy using external optical components to address the low coherence of LEDs 42 , 43 , 44 , 45 . Although effective, these do not fully exploit the advantage of using such a compact light source, as cumbersome interferometric schemes are required and a portable device has not been realized yet.…”

Advances in Digital Holographic Interferometry

“…From (1) and (2) it is obvious that the range of the measured relief Δ z at close values of λ 1 and λ 2 can significantly exceed the limit of λ 1 /2 characteristic of single-wavelength holographic interferometry and reach micro-, milli- or even centimeter range [ 26 ]. At the same time, the resolution of the method is not reduced [ 28 ]. This method makes it possible to reduce speckle noise, which is especially important in the case of using holographic interferometry to study biological objects [ 29 ] and to investigate the dispersion properties of transparent media, which has found wide application in plasma and biology cells diagnostics [ 30 , 31 ].…”

“…For example, there is a double image problem, which consists of the presence of a conjugate wavefront (a double image) during the formation of a hologram, which makes it difficult to reconstruct a multiplex hologram [ 32 ]. This problem is solved by hardware modification of the installation and/or software, which is preferable for digital holographic interferometry [ 27 , 28 , 33 ]. Another problem is caused by the amplification of the noise level in the multiplex hologram: during reconstruction, the phase noise from each of the two spatially superimposed holograms increases by a factor of 2Λ/λ i [ 34 ].…”