This report presents a state-of-the-art multimodality imaging device that combines multi-spectral optoacoustic microscopy (OAM) and optical coherence tomography (OCT) to chart absorbers in live tadpoles (Xenopus laevis) accurately. The OAM channel captures maps of five internal contrast agents: melanin, hemoglobin, collagen, glucose, and lipids. A novel method was developed to achieve this by assuming that each voxel in the 3D-OAM image exhibits a single chromophore contributing to the optoacoustic signal. The device is powered by a single optical source (SuperK Compact, NKT Photonics) that operates across an ultra-wide spectral range of 450 to 2400 nm. The set-up was optimized by minimizing optical aberrations and attenuation on optical components to stimulate the sample effectively. Using optical pulses of 2 ns duration and a repetition rate of 20 kHz, the device imaged tadpoles in their embryonic stage at multiple wavelengths, using narrow spectral windows of 25 nm bandwidth within the broad spectrum of the supercontinuum source at a time. In addition, an ultra-high-resolution OCT imaging channel operating at 1300 nm (spectral bandwidth 180 nm) was created and incorporated into the device. The OCT channel, also powered by a commercial supercontinuum source (SuperK EXTREME EXR9, NKT Photonics), was used for guidance purposes and to help determine the location of the chromophores.
Supercontinuum (SC) lasers are of high interest for applications like multispectral photoacoustic imaging (MSPAI), where the wide optical bandwidth of the SC laser system facilitates functional investigations on top of the structural information of various endogenous agents inside the human body. The current work addresses a promising attempt at devising high pulse energy SC laser source using telecom-range diode laser systems and few meters of standard single-mode fibers for various MSPAI applications in near-infrared (NIR) and extended-NIR wavelength regions.
We report on further progress made on enhancing the capabilities of a multi-imaging modality instrument capable of producing high resolution images of biological tissues. At the core of the instrument is a supercontinuum (SC) source. Two SC sources commercialized by NKT Photonics were employed for our experiments: SuperK COMPACT and SuperK Extreme (EXR9). Using these two sources, we assembled an instrument capable to simultaneously provide in real-time cross-section high-resolution Optical Coherence Tomography (OCT) and Photo-acoustic (PA) images in various spectral ranges. Currently, the OCT channel is operating in the IR range around 1300 nm to allow better penetration into the tissue using either the COMPACT or the EXR9. The measured optical power on the sample is in both cases above 9.5 mW. An in-house spectrometer equipped with a sensitive InGaAs camera capable of operating at 47 kHz and sampling data over a spectral range from 1205 to 1395 nm was developed. A constant axial resolution provided by the instrument in the OCT channel over a range of 1.5 mm was experimentally measured (4.96 μm), matching the theoretical prediction. The spectral range 500-800 nm was used for PA channel. The COMPACT, used in the PA channel, can select the central wavelength and the spectral bandwidth of operations. Typically, the optical energy per pulse on the sample is superior to 60 nJ when a bandwidth superior to 50 nm is employed. This make the instrument usable for PA imaging of tissues.
In this work, an all-solid Ytterbium doped double-clad single-mode (SM) large-mode-area (LMA) photonic crystal fiber (PCF) is characterized in a monolithic amplifier setup. The characterized all-solid PCF combines the SM operation of LMA PCFs while maintaining simple splicing of all-solid fibers. The fiber has been tested in a pulsed monolithic forward pumped amplifier system achieving excellent modal properties. The fiber is polarization maintaining and has a mode field diameter of approximately 24 μm. At optimal fiber length the output signal power of the amplifier was measured to 43 W limited by pump power with an optical to optical efficiency of 61 %. Polarization extinction ratios (PER) above 18 dB was observed for all fiber lengths. Simple splicing with splice losses < 0.2 dB and maintained polarization are reported using a standard Fujikura fusion splicer.
Large-mode-area (LMA) photonic crystal fiber (PCF) amplifiers are attractive for high-power amplification of single-mode (SM) narrow-linewidth light. Traditionally, LMA PCF designs include air holes but splicing and interfacing of fibers with air holes is complicated. Recently, this was addressed with the development of a LMA PCF amplifier fiber without air holes but with SM operation maintained. This all-solid fiber can be spliced with standard splicers and thus enables integration of PCFs into all-fiber monolithic laser systems. The new fiber, named DC-250/30-PM-Yb-FUD, is demonstrated in a free-space configuration for high-power amplification of 1064 nm light with a narrow linewidth of less than 20 kHz. A seed power of 380 mW is amplified to 40 W, corresponding to a single-stage gain of 20 dB, with an optical to optical efficiency of 69%. No indication of stimulated Brillouin scattering is observed, and the output is stable during frequency modulation of the seed laser.
We present a bimodal system driven by a supercontinuum source to perform photoacoustic-based spectral selective absorption measurements from 500 nm to 800 nm and structural optical coherence tomography imaging at 1300 nm. An energy of 5 to 40 nJ is achieved on sample within a 50 nm bandwidth in the visible range in the photoacoustic channel. Also, a few mW power is also achieved on the sample in the optical coherence tomography channel.
Supercontinuum (SC) light is a well-established technology, which finds applications in several domains ranging from chemistry to material science and imaging systems [1-2]. More specifically, its ultra-wide optical bandwidth and high average power make it an ideal tool for Optical Coherence Tomography (OCT). Over the last 5 years, numerous examples have demonstrated its high potential [3-4] in this context. However, SC light sources present pulse-to-pulse intensity variation that can limit the performance of any OCT system [5] by degrading their signal to noise ratio (SNR). To this goal, we have studied and compared the noise of several SC light sources and evaluated how their noise properties affect the performance of Ultra-High Resolution OCT (UHR-OCT) at 1300 nm. We have measured several SC light sources with different parameters (pulse length, energy, seed repetition rate, etc.).
We illustrate the different noise measurements and their impact on a state of the art UHR-OCT system producing images of skin. The sensitivity of the system was higher than 95 dB, with an axial resolution below 4μm.
We demonstrate a record bandwidth high energy supercontinuum source suitable for multispectral photoacoustic microscopy. The source has more than 150 nJ/10 nm bandwidth over a spectral range of 500 to 1600 nm. This performance is achieved using a carefully designed fiber taper with large-core input for improved power handling and small-core output that provides the desired spectral range of the supercontinuum source.
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