Naoki Fukutake

Proposal of three-dimensional phase contrast holographic microscopy

We propose a three-dimensional phase contrast digital holographic microscopy. The object to be observed is a low-contrast transparent refractive index distribution sample, such as biological tissue. Low contrast phase objects are converted to high contrast images through the microscopy we propose. In order to gain high three-dimensional resolution, the direction of pump plane wave is scanned, and separate holographic images produced at each angle are acquired and decoded into complex amplitude in Fourier space. The three-dimensional image is reconstructed in a computer from all information acquired through the system. The resolution in the direction of the optical axis is increased by utilizing a 4π configuration of objective lenzes.

Comparison of image-formation properties of coherent nonlinear microscopy by means of double-sided Feynman diagrams

We report a theoretical study on the optical resolution of coherent nonlinear microscopy by means of double-sided Feynman diagrams. Through the use of the diagrams, we offer a simple technique to calculate the coherent transfer function (CTF), which is employed as the indicator of the optical resolution. In particular, we deal with the CTFs of coherent anti-Stokes Raman scattering (CARS) microscopy and stimulated Raman scattering (SRS) microscopy. Our results show that CARS and SRS microscopy possess nearly identical optical resolutions if a molecular-vibrational frequency of interest is assumed to be negligible compared with excitation photon energy. The peculiar image-formation properties of third-harmonic generation (THG) microscopy also can be explained by our technique.

Electronically resonant third-order sum frequency generation spectroscopy using a nanosecond white-light supercontinuum

Third-order sum frequency generation (TSFG) is one of the third-order nonlinear optical processes, and has the generation mechanism analogous to third harmonic generation (THG). By using a white-light supercontinuum, we can obtain broadband multiplex TSFG spectra. In the present study, we developed an electronically resonant TSFG spectrometer, and applied it to obtain TSFG spectra of hemoproteins. Analyzed TSFG ratio spectra clearly showed the resonant enhancement attributable to the electronic state of hemoproteins. This is a promising method for the imaging of electronic states of molecules inside living cells or tissues.

Resolution properties of nonlinear optical microscopy.

We analyze the resolution properties of nonlinear optical microscopy systems that use nonlinear optical effects, such as multiphoton-excited fluorescence, second- and third-harmonic generation, coherent anti-Stokes Raman scattering, and stimulated-emission depletion. Image formation formulas are presented that unitedly describe the properties of the image observed, wherein coherent, incoherent, or mixed-coherent phenomena are utilized. We develop the formalism for the optical resolution of all types of nonlinear systems. The properties of image formation represented by the transmission cross-coefficient are different depending on the type of nonlinear systems.

Theoretical consideration on quantum lithography with conventional projection

At the end of last century, the name of “quantum lithography” has been emerged. This exciting approach was proposed for making a resolution two times higher than that of the conventional optics without changing a wavelength and a numerical aperture. For those who want optical lithography to last long, this has been thought to be a great technology. However, an applicability of the proposed method to the current exposure system i.e., reduced projection exposure system has not yet been examined clearly. We have investigated the proposed quantum lithography to apply into the current exposure system using reticle. For simplicity, coherent illumination i.e. sigma is zero condition is used for calculation. Our quantum lithography compatible to mask exposure system explains probability of one and two photon absorption on the image plane i.e. on wafer. We have shown that the half-wavelength quantum lithography using conventional mask exposure system is impossible because diffraction at the mask makes biphoton into two photon. We have found that there is still super-resolution quantum lithography using mask exposure, however, there is little possibility of quantum lithography practically today because biphoton light source is as dark as stars. To realize quantum lithography practically, further development of not only biphoton light source but also two-photon absorption resist is indispensable.

Coherent transfer function of Fourier transform spectral interferometric coherent anti-Stokes Raman scattering microscopy

We analyze the optical resolution of Fourier transform spectral interferometric-coherent anti-Stokes Raman scattering microscopy, which extracts the complex amplitude of an image by using a spectral interferometric effect. Image-formation formulas are presented that describe the properties of the image observed by the apparatus. The image-formation properties represented by the coherent transfer function are different depending on the mode (transmission, reflection, etc.) of the microscopy.

Proposal of three-dimensional phase contrast holographic microscopy: erratum

We propose a three-dimensional phase contrast digital holographic microscopy. The object to be observed is a low-contrast transparent refractive index distribution sample, such as biological tissue. Low contrast phase objects are converted to high contrast images through the microscopy we propose. In order to gain high three-dimensional resolution, the direction of pump plane wave is scanned, and separate holographic images produced at each angle are acquired and decoded into complex amplitude in Fourier space. The three-dimensional image is reconstructed in a computer from all information acquired through the system. The resolution in the direction of the optical axis is increased by utilizing a 4pi configuration of objective lenzes.

Projection lithography by means of parametric photon pairs

It is well known that entangled-photon pairs generated by spontaneous parametric down-conversion exhibit a property that is analogous to that of ordinary incoherent lights. We formulate an image-forming optical theory of quantum lithography that comprehends the both conceptions of partial coherence and partial entanglement by extending a classical image-forming optical theory. Our optical system consists of an image-forming system, an illumination system with a second-order nonlinear medium, and two-photon absorbing materials. We evaluate the resolution of the quantum lithography system by using the optical transfer function and show a special case to be a super-resolving system.

Superresolution fluorescence imaging by pump-probe setup using repetitive stimulated transition process

We proposed superresolution nonlinear fluorescence microscopy with pump-probe setup that utilizes repetitive stimulated absorption and stimulated emission caused by two-color laser beams. The resulting nonlinear fluorescence that undergoes such a repetitive stimulated transition is detectable as a signal via the lock-in technique. As the nonlinear fluorescence signal is produced by the multi-ply combination of incident beams, the optical resolution can be improved. A theoretical model of the nonlinear optical process is provided using rate equations, which offers phenomenological interpretation of nonlinear fluorescence and estimation of the signal properties. The proposed method is demonstrated as having the scalability of optical resolution. Theoretical resolution and bead image are also estimated to validate the experimental result.

Phase-shift effect of amplitude spread function on spectrum and image formation in coherent Raman scattering microspectroscopy.

Coherent Raman scattering microspectroscopy, which includes coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS) microspectroscopy, permits label-free hyperspectral imaging. We report the theoretical study of the phase-shift effect of the impulse response function on the spectral and image-forming properties of coherent Raman scattering microspectroscopy. We show that the spectrum and image are influenced by not only the NA of objective for excitation (NA(ex)) but also that for signal collection (NA(col)), in association with the phase-shift effect. We discuss that, under the condition NA(ex)≠NA(col), both the spectrum and the image become deformed by the phase-shift effect, which can be applied to the direct measurement of the imaginary part of the nonlinear susceptibility in CARS spectroscopy. We point out that, even in SRS microscopy, the nonresonant background can contribute to the image formation and cause the artifact in the image.