Laser Science Laboratory
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Laser Science Laboratory is a new laboratory started in April 2019. We have knowledge and technology to design and build lasers with top-class performance in the world. For example, we have developed a laser which generates the world shortest 7 femtosecond infrared light pulses, and a high-performance ultrafast fiber laser which uses a fluoride fiber as a laser medium.
We also have a unique technology which allows us to directly measure light waves oscillating with a period of several femtoseconds. In addition, we are conducting joint research projects with life science laboratories and companies.
When high-intensity light is focused into a medium under certain conditions, the increase in the refractive index due to nonlinear effects is balanced with the decrease in the refractive index due to the plasma generated by the multiphoton ionization, and the light propagates over a long distance with a very small diameter. This phenomenon is known as filamentation. Using this filamentation effect, we have succeeded in generating the world's shortest 7 femtosecond mid-infrared light pulse[e.g., IEEE J. Sel. Top. Quantum Electron. 21 8700612 (2015), Opt. Express 28 36527 (2020)]. This is a breakthrough technique that can easily generate extremely short pulses in which the electromagnetic field oscillates only once.
In addition, we are developing high-speed infrared spectroscopy, femtosecond pump-probe spectroscopy, and hyperspectral imaging using the ultimately short mid-infrared pulses [e.g., J. Opt. 17 094004 (2015), Nat. Commun. 14 3929 (2023)]. In the future, we aim to apply this technology to various scientific and industrial fields, such as environmental science, life science, and medicine.
It is well known that light has wave nature. However, it is still very difficult to directly measure the wave of light even with the most advanced technology.
The principal investigator of this laboratory has developed new methods to measure the waveforms of light [e.g., Nat. Commun. 4 2820 (2013), Optica 10 302 (2023)]. These are considered to be useful methods for the studies on such as high-field physics, ultrafast optical signal processing, and synchrotron light source development. Currently, we are developing the technology so that this method can be used in different wavelength ranges.
Femtosecond lasers in the 1.3–2.1 μm wavelength range are expected to be useful for the applications such as deep observation of biological tissues, advanced semiconductor microfabrication, and broadband coherent mid-infrared light generation. We are developing such lasers in collaboration with companies such as FiberLabs Inc.
Recently, we have developed a high-power 1.94 μm laser system that generates laser pulses with a duration of 265 fs and a pulse energy of 1 mJ, and have applied it to broadband coherent mid-infrared light generation [Opt. Express 30 7332 (2022)]. We have also developed 1.3 and 1.8 μm fiber lasers, and have successfully observed neurons in the brain of a living mouse in collaboration with the National Institute for Physiological Sciences [Opt. Express 31 16127 (2023), Biomed. Opt. Express 14 326 (2023)]. We believe that the commercialization of these lasers will contribute significantly to the advancement of brain research.
Nano and micro particles can be pushed, trapped and manipulated by using a focused laser beam. This is due to a "radiation force" which is induced on the particles by the laser. Its magnitude and direction actually depend on an induced polarization (how the electrons in the particles are oscillated by the electromagnetic wave laser). A transparent, non-resonant, laser is typically used for this optical trapping research. Prof. T. Kudo et al. have been working on the optical trapping researches when the laser is resonant to the particles in various ways.
We conducted the optical trapping theory and experiment when the trapping laser is resonant to electronic transition of the particles, especially in nonlinear optical regions [PRL 109, 087402 (2012),Opt. Exp. 25, 4655 (2017)]. We also found unprecedented assembling phenomena, called optically evolved assembly, when the trapping laser is resonant to surface plasmon resonance of metallic nanoparticles [Nano Lett. 18, 5846 (2018)], photonic bandgap of colloidal photonic crystals [Nano Lett. 16, 3058 (2016)] and whispering gallery mode of microspheres [J. Phy. Chem. Lett. 11, 6057 (2020)]. All of these results are based on the strong light and matter interaction under the optical trapping. Currently, we are working on resonant optical trapping using the laser techniques in our laboratory.
Midinfrared light is extensively used for identifying molecules because their characteristic vibrational modes commonly exist in the midinfrared spectral region.
We recently found that optical force can be resonantly enhanced when vibrational modes of target particles are excited by mid-infrared laser[Phys. Rev. Applied 18, 054041 (2022)]. Silica particles rapidly transport in the 9 μm mid-infrared evanescent wave (top video) since their vibrational mode (Si-O-Si bonds) is excited, while the polystyrene particles are not transported (bottom video) because their vibrational mode is not excited by the laser. We believe that this technique can be used for optical force chromatography according to molecular structures.
Different from the optical force, particles are migrated along the temperature gradient which is caused by laser absorption. This is known as opto-thermophoresis and/or optothermal trapping. 1.4 to 1.5 μm lasers were used for these studies in the past. In the spectrum, water has absorption peaks around 1.5, 2 μm, respectively, related to O-H bonds.
Here, we used 2 μm infrared laser to excite the vibrational modes of water for heating water[Opt. Exp. 29, 38314 (2021)]. Currently we are developing further efficient optothermal trapping with fiber based laser system.