The transport-of-intensity equation (TIE) is a computational approach to reconstruct the phase of a complex wave in optical and electron microscopy. It describes the internal relationship between the intensity and phase distribution of a wave.
The TIE was first proposed in 1983 by Michael Reed Teague. Teague suggested to use the law of conservation of energy to write a differential equation for the transport of energy by an optical field. This equation, he stated, could be used as an approach to phase recovery.
where is the wavelength, is the irradiance at point , and is the phase of the wave. If the intensity distribution of the wave and its spatial derivative can be measured experimentally, the equation becomes a linear equation that can be solved to obtain the phase distribution .
For a phase sample with a constant intensity, the TIE simplifies to
It allows measuring the phase distribution of the sample by acquiring a defocused image, i.e. .
The TIE utilizes only object field intensity measurements at multiple axially displaced planes, without any manipulation of the object and reference beams.
TIE-based approaches are applied in biomedical and technical applications, such as quantitative monitoring of cell growth in culture, investigation of cellular dynamics and characterization of optical elements. The TIE method is also applied for phase retrieval in transmission electron microscopy.
- Bostan, E. (2014). "Phase Retrieval by Using Transport-of-Intensity Equation and Differential Interference Contrast Microscopy". IEEE International Conference on Image Processing (ICIP): 3939–3943. doi:10.1109/ICIP.2014.7025800. ISBN 978-1-4799-5751-4. S2CID 10310598.
- Cheng, H. (2009). "Phase Retrieval Using the Transport-of-Intensity Equation". IEEE Fifth International Conference on Image and Graphics: 417–421. doi:10.1109/ICIG.2009.32. ISBN 978-1-4244-5237-8. S2CID 15772496.
- Teague, Michael R. (1983). "Deterministic phase retrieval: a Green's function solution". Journal of the Optical Society of America. 73 (11): 1434–1441. doi:10.1364/JOSA.73.001434.
- Nugent, Keith (2010). "Coherent methods in the X-ray sciences". Advances in Physics. 59 (1): 1–99. arXiv:0908.3064. Bibcode:2010AdPhy..59....1N. doi:10.1080/00018730903270926. S2CID 118519311.
- Gureyev, T. E.; Roberts, A.; Nugent, K. A. (1995). "Partially coherent fields, the transport-of-intensity equation, and phase uniqueness". JOSA A. 12 (9): 1942–1946. Bibcode:1995JOSAA..12.1942G. doi:10.1364/JOSAA.12.001942.
- Huang, Lei; Zuo, Chao; Idir, Mourad; Qu, Weijuan; Asundi, Anand (2015). "Phase retrieval with the transport-of-intensity equation in an arbitrarily shaped aperture by iterative discrete cosine transforms". Optics Letters. 40 (9): 1976–1979. Bibcode:2015OptL...40.1976H. doi:10.1364/OL.40.001976. OSTI 1193230. PMID 25927762.
- Curl, C.L. (2004). "Quantitative phase microscopy: a new tool for measurement of cell culture growth and confluency in situ". PFLugers Archiv - European Journal of Physiology. 448 (4): 462–468. doi:10.1007/s00424-004-1248-7. PMID 14985984. S2CID 7640406.
- Dorrer, C. (2007). "Optical testing using the transport-of-intensity equation". Opt. Express. 15 (12): 7165–7175. Bibcode:2007OExpr..15.7165D. doi:10.1364/oe.15.007165. PMID 19547035.
- Belaggia, M. (2004). "On the transport of intensity technique for phase retrieval". Ultramicroscopy. 102 (1): 37–49. doi:10.1016/j.ultramic.2004.08.004. PMID 15556699.