Compact light source for ultrabroadband coherent anti-Stoke Raman scattering (CARS) microscopy

Label-free enzymatic reaction monitoring in water-in-oil microdroplets using ultra-broadband multiplex coherent anti-Stokes Raman scattering spectroscopy

We propose a system for monitoring an enzymatic reaction, i.e., dehydrogenation of ethanol catalyzed by alcohol dehydrogenase, in microdroplets using ultra-broadband multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy. The reaction solution was encapsulated in water-in-oil microdroplets with diameters of 50 µm. The reaction was monitored by measuring the concentration of coenzymes from the CARS spectrum obtained in one-second exposure time. The results obtained using our system was consistent with those of the conventional fluorescence measurement system and indicate the potential of CARS spectroscopy for droplet-based high-throughput screening of enzymes.

Low-repetition-rate all-fiber integrated optical parametric oscillator for coherent anti-Stokes Raman spectroscopy

All-fiber optical parametric oscillator (OPO), offering advantages like robustness, compactness and low lost, has attracted intense interest in coherent anti-Stokes Raman scattering spectroscopy. In typical fiber-based OPO configurations, detrimental nonlinear effects due to intense pump field in fiber coupling devices would inevitably degrade the spectral purity and conversion efficiency, especially when the OPO operated at low repetition rates. Here we demonstrated a new OPO design by placing the main amplifier inside the cavity, where the amplified pump pulses were directly coupled into the nonlinear fiber. Consequently, lower threshold, higher output power and narrower spectrum were obtained. In particular, effective suppression of spectral noise was experimentally observed, resulting in threshold reductions of 37.5%, 17.2%, and 5.2% with a comparison to a conventional OPO operating at repetition rates of 1, 2 and 3 MHz, respectively. Furthermore, the generated synchronized two-color laser sources at a low repetition rate were then employed to detect CH vibrational bands in an ethanol sample. This spectral tailored cavity design is expected to greatly promote the spread of compact all-fiber laser source to nonlinear biomedical imaging.

Developments in spontaneous and coherent Raman scattering microscopic imaging for biomedical applications

First, the potential role of Raman-based techniques in biomedicine is introduced. Second, an overview about the instrumentation for spontaneous and coherent Raman scattering microscopic imaging is given with a focus of recent developments. Third, imaging strategies are summarized including sequential registration with laser scanning microscopes, line imaging and global or wide-field imaging. Finally, examples of biomedical applications are presented in the context of single cells, laser tweezers, tissue sections, biopsies and whole animals.

Design and analysis of a highly nonlinear composite photonic crystal fiber for supercontinuum generation: visible to mid-infrared

A composite photonic crystal fiber structure has been designed with tellurite as the cladding and chalcogenide as a core material. To increase nonlinearity, rods of the chalcogenide glass material have been inserted around the core region. The reported structure offers very high nonlinearity of 1042  W^-1 Km^-1 at 2800 nm pump wavelength with low and flattened dispersion of approximately -11  ps·nm^-1 Km^-1. An effective mode area of 6.46  μm² of the propagating mode has been achieved as at pump wavelength. Such a highly nonlinear composite photonic crystal fiber structure is a potential candidate for nonlinear applications, such as slow-light and supercontinuum generation. Pumping at 2800 nm results in a supercontinuum spectrum spanning 0.5-4.7 μm using 8 mm long photonic crystal fiber pumped with femtosecond laser pulses with peak power of 3 kW.

Visible to near-infrared supercontinuum generation in yttrium orthosilicate bulk crystal and ion implanted planar waveguide

This paper reports on the supercontinuum generation in yttrium orthosilicate bulk crystal and 6-mm-long ion implanted planar waveguide. The waveguide is fabricated by 6 MeV oxygen ions implantation with fluence of 5 × 10¹⁴ ions/cm² at room temperature. The yttrium orthosilicate bulk crystal and waveguide are pumped using a mode-locked Ti:Sapphire laser with a center wavelength of 800 nm. The generated broadest supercontinuum spans 720 nm (at −30 dB points) from 380 to 1100 nm in bulk crystal and 510 nm (at −30 dB points) from 490 to 1000 nm in ion implanted waveguide, respectively. Compared to the bulk crystal, the ion implanted waveguide requires almost three orders of magnitude lower pump power to achieve a similar level of broadening. The supercontinuum is generated in the normal dispersion regime and exhibits a relatively smooth spectral shape. Our research findings indicate that ion implantation is an efficient method to produce waveguide in yttrium orthosilicate crystal for low-threshold supercontinuum generation.

Coherent anti-Stokes Raman scattering hyperspectral imaging of cartilage aiming for state discrimination of cell

Noninvasive cell analyses are increasingly important in the medical field. A coherent anti-Stokes Raman scattering (CARS) microscope is the noninvasive imaging equipment and enables to obtain images indicating molecular distribution. However, due to low-signal intensity, it is still challenging to obtain images of the fingerprint region, in which many spectrum peaks correspond to compositions of a cell. Here, to identify cell differentiation by using multiplex CARS, we investigated hyperspectral imaging of the fingerprint region of living cells. To perform multiplex CARS, we used a prototype of a compact light source generating both pump light and broadband Stokes light. Assuming application to regenerative medicine, we chose a cartilage cell, whose differentiation is difficult to be identified by change of the cell morphology. Because one of the major components of cartilage is collagen, we focused on distribution of proline, which accounts for approximately 20% of collagen. The spectrum quality was improved by optical adjustments of the power branching ratio and divergence of Stokes light. Periphery of a cartilage cell was highlighted in a CARS image of proline, and this result suggests correspondence with collagen generated as an extracellular matrix. The possibility of noninvasive analyses by using CARS hyperspectral imaging was indicated.

Compact and fully collinear light source for broadband multiplex CARS microscopy covering the fingerprint region

Compact and fully collinear light source for multiplex coherent anti-Stokes Raman scattering (CARS) microscopy was proposed and demonstrated. It consists of only a microchip laser, a short photonic crystal fiber, and a longpass filter. It offers performance of sensitivity, bandwidth, and spectral resolution suitable for biomedical applications, especially covering the entire fingerprint region (500-1800 cm(-1)). It can be readily implemented by a commercially available microchip laser and a photonic crystal fiber. It has great potential to expand the utility of CARS microscopy to a wide variety of fields such as endoscopy.

Visible-to-near-infrared octave spanning supercontinuum generation in a silicon nitride waveguide

The generation of an octave spanning supercontinuum covering 488-978 nm (at -30  dB) is demonstrated for the first time on-chip. This result is achieved by dispersion engineering a 1-cm-long Si3N4 waveguide and pumping it with an 100-fs Ti:Sapphire laser emitting at 795 nm. This work offers a bright broadband source for biophotonic applications and frequency metrology.