Principles of Non-Linear Imaging


Linear spectroscopy has enabled great discoveries but the contrast that is found in linear (visible) microscopy is not always optimal; Characteristic absorptions are often in the UV or IR. To reach these absorption lines multi-photon difference- or sum-frequencies can be used so that much more contrast is generated from similar input. Additionally the selection rules for multi-photon processes can provide contrast; centro-symmetric system do not support second or third harmonic generation which means that sites that break the symmetry (surfaces or small particles) can be revealed. Sum frequency can be done with two visible photons but also acoustic waves can be used. Non-resonant parametric processes tend to be phase–preserving, allowing for interferometric or heterodyne detection. All these aspects of nonlinear imaging as well as the choices for practical implementations will be discussed.


1. Linear polarization, harmonic oscillator, refractive index and absorption
2. Nonlinear polarization, generation, phase matching
3. Selection rules, crystals, birefringent phase matching, periodic phase matching
4. Different orders of nonlinearity, SHG, THG, DFG, CARS, CSR, SBS, STED, NLSIM, NL_fluorescence.
5. Microscopy, linear imaging and types of nonlinear imaging
6. Spontaneous Raman, Stimulated Raman, phase aspects, bandwidth, focal/temporal engineering, Nonlinear background
7. CARS microscopy implementations, experimental aspects
8. Image processing, hyperspectral data, PCA, classification algorithms, end-members
9. Application examples, chemical imaging, biological/medical imaging
10. Quantum optics, squeezing, ghost imaging, single-photons.

Learning Outcomes

To give students an understanding of the mechanism that govern non-linear optical imaging and present an overview of possibilities offered by these techniques


Slides and articles

External Evaluator

To be announced

Responsible Academic

Herman Offerhaus (University of Twente)

Awarded ECTS