Takuro Ideguchi

Broadband coherent Raman spectroscopy running at 24,000 spectra per second.

We present a Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS) spectroscopy technique that achieves broadband CARS measurements at an ultrahigh scan rate of more than 20,000 spectra/s – more than 20 times higher than that of previous broadband coherent Raman scattering spectroscopy techniques. This is made possible by an integration of a FT-CARS system and a rapid-scanning retro-reflective optical path length scanner. To demonstrate the technique’s strength, we use it to perform broadband CARS spectroscopy of the transient mixing dynamics of toluene and benzene in the fingerprint region (200–1500 cm−1) with spectral resolution of 10 cm−1 at a record high scan rate of 24,000 spectra/s. Our rapid-scanning FT-CARS technique holds great promise for studying chemical dynamics and wide-field label-free biomedical imaging.

High-throughput optofluidic particle profiling with morphological and chemical specificity

We present a method for high-throughput optofluidic particle analysis that provides both the morphological and chemical profiles of individual particles in a large heterogeneous population. This method is based on an integration of a time-stretch optical microscope with a submicrometer spatial resolution of 780 nm and a three-color fluorescence analyzer on top of an inertial-focusing microfluidic device. The integrated system can perform image- and fluorescence-based screening of particles with a high throughput of 10,000 particles/s, exceeding previously demonstrated imaging particle analyzers in terms of specificity without sacrificing throughput.

Kerr-lens mode-locked bidirectional dual-comb ring laser for broadband dual-comb spectroscopy

Fourier-transform spectroscopy is an indispensable tool for analyzing chemical samples in scientific research as well as the chemical and pharmaceutical industries. Recently, its measurement speed, sensitivity, and precision have been shown to be significantly enhanced by using dual-frequency combs. Moreover, recent demonstrations of inducing nonlinear effects with ultrashort pulses have enriched the utility of dual-comb spectroscopy. However, wide acceptance of this technique is hindered by its requirement for two frequency combs and active stabilization of the combs. Here, we overcome this predicament with a Kerr-lens mode-locked bidirectional ring femtosecond-pulse laser that generates two broadband frequency combs with slightly different pulse repetition rates and a tunable yet highly stable rate difference. Since these combs are produced by one and the same laser cavity, their relative coherence stays passively stable without the need for active stabilization. To show its utility, we demonstrate broadband dual-comb spectroscopy with the single laser.

High-throughput time-stretch microscopy with morphological and chemical specificity

Particle analysis is an effective method in analytical chemistry for sizing and counting microparticles such as emulsions, colloids, and biological cells. However, conventional methods for particle analysis, which fall into two extreme categories, have severe limitations. Sieving and Coulter counting are capable of analyzing particles with high throughput, but due to their lack of detailed information such as morphological and chemical characteristics, they can only provide statistical results with low specificity. On the other hand, CCD or CMOS image sensors can be used to analyze individual microparticles with high content, but due to their slow charge download, the frame rate (hence, the throughput) is significantly limited. Here by integrating a time-stretch optical microscope with a three-color fluorescent analyzer on top of an inertial-focusing microfluidic device, we demonstrate an optofluidic particle analyzer with a sub-micrometer spatial resolution down to 780 nm and a high throughput of 10,000 particles/s. In addition to its morphological specificity, the particle analyzer provides chemical specificity to identify chemical expressions of particles via fluorescence detection. Our results indicate that we can identify different species of microparticles with high specificity without sacrificing throughput. Our method holds promise for high-precision statistical particle analysis in chemical industry and pharmaceutics.

Thermal distribution of Cu 2 O paraexcitons in a strain-induced trap probed by excitonic Lyman spectroscopy

We observe the signal of trapped paraexcitons in Cu2O by using CW excitonic Lyman spectroscopy. The temperature dependence of the 1s-2p induced absorption of paraexcitons indicates the presence of a strain-induced trap.

Phase-controlled Fourier-transform spectroscopy

Fourier-transform spectroscopy (FTS) has been widely used as a standard analytical technique over the past half-century. FTS is an autocorrelation-based technique that is compatible with both temporally coherent and incoherent light sources, and functions as an active or passive spectrometer. However, it has been mostly used for static measurements due to the low scan rate imposed by technological restrictions. This has impeded its application to continuous rapid measurements, which would be of significant interest for a variety of fields, especially when monitoring of non-repeating or transient complex dynamics is desirable. Here, we demonstrate highly efficient FTS operating at a high spectral acquisition rate with a simple delay line based on a dynamic phase-control technique. The independent adjustability of phase and group delays allows us to achieve the Nyquist-limited spectral acquisition rate over 10,000 spectra per second, while maintaining a large spectral bandwidth and high resolution. We also demonstrate passive spectroscopy with an incoherent light source.Fourier transform spectrometers are generally limited to slow scanning rates at high resolution. Here the authors demonstrate highly efficient Fourier transform spectroscopy using a dynamic phase-control technique that enables fast acquisition without compromising bandwidth or resolution.

Ultrafast broadband Fourier-transform CARS spectroscopy operating at 50,000 spectra/second

We present a coherent Raman scattering (CRS) spectroscopy technique achieving a CRS spectral acquisition rate of 50,000 spectra/second over a Raman spectral region of 200 - 1430 cm-1 with a resolution of 4.2 cm-1. This ultrafast, broadband and high-resolution CRS spectroscopic performance is realized by a polygonal Fourier-domain delay line serving as an ultra-rapid optical-path-length scanner in a broadband Fourier-transform coherent anti-Stokes Raman scattering (CARS) spectroscopy platform. We present a theoretical description of the technique and demonstrate continuous, ultrafast, broadband, and high-resolution CARS spectroscopy on a liquid toluene sample using our proof-of-concept setup.

Evaluation of density-dependent lifetime of 1s paraexcitons in Cu 2 O by cw laser based excitonic Lyman spectroscopy

The lifetime and the Auger coefficient for 1s paraexctons in Cu2O from 5 K to 70 K was measured directly using excitonic Lyman spectroscopy. A possible experiment for realizing excitonic Bose-Einstein condensation is discussed.

Coherent control of resonant two-photon excitation of excitons in Cu 2 O by phase modulated pulses

By using a pulse shaping method, we control the resonant two-photon excitation probability of 1s orthoexcitons in Cu2O and suppress the undesired three-photon interband transition which emerges at a high power excitation.

Laser based continuous-wave excitonic Lyman spectroscopy of spin-forbidden excitons in Cu 2 O

We developed a sensitive method to detect 1s paraexcitons in Cu2O by using cw laser-based excitonic Lyman spectroscopy with a tunable Cu2O laser. The paraexcitons were found to have a lifetime of microseconds.