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Ultrafast Fiber Lasers
Published in Iniewski Krzysztof, Integrated Microsystems, 2017
The 1 W, 100 fs fiber laser has a pulse repetition rate of 33 MHz, compressed pulse energy of 30 nJ, and an average power of 1.4 W. With an operating wavelength around 1035 nm, the actual measured pulse width is 90 fs with a Gaussian shape assumption (see Figure 20.15). It has a compact compressor integrated with the fiber laser for ease of operation and reliability. For a pulse width of 200 fs, output power levels as high as 5 W compressed have been achieved. Further optimization can be performed toward a pulse width of 100 fs. And by adding an optical parametric oscillator as a supplement, the wavelength can cover from the visible to mid-IR range, further extending the capability of fs fiber lasers.
Chemical and Molecular Imaging of Deep Tissue through Photoacoustic Detection of Chemical Bond Vibrations
Published in Lingyan Shi, Robert R. Alfano, Deep Imaging in Tissue and Biomedical Materials, 2017
R. Li et al. proposed and demonstrated a multispectral VPAT based imaging modality to detect breast cancer margin [64]. The schematic setup for their imaging system is shown in Fig. 14.6a. Nd:YAG pumped optical parametric oscillator (OPO) with a 10 Hz repetition rate and 5 ns pulse width is used as the excitation source. The wavelength of the OPO was tuned from 1100 to 1250 nm, which includes the strong absorption of hemoglobin and second overtone absorption band of lipid, with 10 nm step size to perform multispectral photoacoustic imaging. Optical energy was delivered to the specimen by a fiber bundle with two rectangular distal terminals, which is stick to each side of an ultrasound transducer array in parallel. The generated photoacoustic signals were detected by ultrasound transduce array with 128 elements and sent to a high-frequency ultrasound imaging system for image reconstruction.
Molecular Vibrational Imaging by Coherent Raman Scattering
Published in Shoogo Ueno, Bioimaging, 2020
Yasuyuki Ozeki, Hideaki Kano, Naoki Fukutake
To date, various techniques have been developed for generating two-color synchronized optical pulses, which are categorized into two types, namely, active synchronization and passive synchronization. In active synchronization, two independent lasers are used to generate two-color pulses, and the repetition rate of one laser is controlled to synchronize it with the other laser. In passive synchronization, two-color laser pulses can be generated without external active control by utilizing some interaction between two lasers. Previous studies on CARS microscopy [1,2] used passively synchronized laser sources, including an optical parametric amplifier (OPA), which can generate synchronized wavelength-tunable pulses. However, OPAs typically have a low repetition rate of <1 MHz, and therefore are incompatible for high-speed imaging. Then, actively synchronized Ti:sapphire lasers were adopted in CARS microscopy, and significant efforts have been made to realize synchronization with a low timing jitter [34,35]. Ti:sapphire oscillators can generate wavelength-tunable picosecond pulses with a narrow spectral width at a high repetition rate of ~80 MHz; thus, they are found to be suitable for CARS microscopy. However, active synchronization is typically very sensitive to environmental perturbations, including physical shock and temperature change, which hinders the widespread use of CRS microscopy. Then, OPOs [36,37] were developed, which have become the most popular laser sources for CARS and SRS microscopy systems because OPO allows passive synchronization, which is typically significantly more stable than active synchronization. The OPO is excited by a pulse train from a master laser, and the pulse train can give rise to an optical parametric gain in a nonlinear optical crystal in the OPO cavity only when the pulses pass through the crystal; therefore, optical pulses that are synchronized with the master laser pulses can be generated. Further, various laser configurations have been adopted as master laser sources, including mode-locked solid-state laser oscillators using Nd:YVO4 as a gain material [37]. Currently, mode-locked Yb fiber lasers, which can generate ~3 ps pulses of wavelength ~1032 nm at a repetition rate of ~80 MHz, are the most popular [36]. If an OPO pumped by frequency-doubled Yb fiber laser pulses (516 nm) is used as a laser source, the signal from the OPO (690–990 nm) and the fundamental output from the Yb fiber laser (1032 nm) can be used as optical pulses at ωp and ωS, respectively. Although OPO has a high wavelength tunability, wavelength tuning requires temperature control of the OPO crystal, as well as the mechanical control of birefringent filter inside the OPO cavity; thus, wavelength tuning requires several tens of seconds to several minutes.
Engineering polymeric nanocapsules for an efficient drainage and biodistribution in the lymphatic system
Published in Journal of Drug Targeting, 2019
Ana Sara Cordeiro, José Crecente-Campo, Belén L. Bouzo, Santiago F. González, María de la Fuente, María José Alonso
For the 3D reconstruction imaging studies experiments, popliteal and lumbar lymph nodes of the mice being studied were harvested at 12 h post-injection and kept in PBS at 4 °C. One axillary lymph node was also collected at the same time as a control. Lymph node imaging was done using a customised 2-photon platform (TrimScope, LaVision BioTec GmbH; Bielefeld, Germany). 2-Photon excitation of the fluorescent probes was achieved using two tuneable Ti:Sapphire lasers with an output wavelength in the range of 690–1080 nm (Chamaleon Ultra I, Chamaleon Ultra II, Coherent Inc.; Santa Clara, CA), and an optical parametric oscillator emitting in the range of 1010–1340 nm (Chamaleon Compact OPO, Coherent Inc.; Santa Clara, CA). The objective used to obtain 3 D whole lymph node reconstructions was a Nikon Plan Apo λ 10×/0.45, with a mosaic of up to 4 × 3 adjacent field-of-view image acquisitions.
Lung deposition patterns of MWCNT vary with degree of carboxylation
Published in Nanotoxicology, 2019
Andrij Holian, Raymond F. Hamilton, Zhequion Wu, Sanghamitra Deb, Kevin L. Trout, Zhiqian Wang, Rohit Bhargava, Somenath Mitra
Stimulated Raman Scattering (SRS) was used in order to further confirm CytoViva results and to analyze larger regions of tissue at higher resolution. The images of unstained lung tissue sections were acquired using a SRS imaging setup built in house, which is based on a two-photon laser scanning microscopy system (Kole 2017). The home built SRS microscope is integrated with a dual-output (1064 nm/532 nm, 80 MHz) ultrafast oscillator (Lumera, Coherent Germany) coupled into an optical parametric oscillator (OPO) (Levante Emerald, APE Germany) to provide tunable (750 nm–970 nm) ∼ 6 picosecond pulse trains. The 1064 nm output from the oscillator is used as the Stokes beam and the output from the OPO is used as the pump beam, which is tuned to match a Raman mode of interest. The Stokes pulse train (1064 nm) is amplitude-modulated at 7 MHz by an electro-optic modulator (EOM, Conoptics) and beams are spatiotemporally overlapped and sent collinearly to the SRS microscope. The images were acquired using a 50 × (0.95 NA, Zeiss) objective and a custom-built large area photodiode (PS100-6, First sensor) detector. A high OD band-pass filter (Chroma Technology, 890/220m) was used to selectively transmit the pump beam and to block the Stokes beam for stimulated Raman Loss (SRL) detection (Freudiger et al. 2008). The SRL signals (based on transferred modulation from the Stokes beam to the pump beam), thus acquired, were demodulated and amplified by a lock-in amplifier (HF2LI, Zurich Instruments) with a time constant of 5 µs. Images were acquired with 20 μs pixel dwell time at two different Raman frequencies with different laser powers: 2700 cm−1 at <1.5mW at sample plane and 2930 cm−1 at 30 mW total power. The 2700 cm−1 frequency was at very low power because higher power caused significant photo-damage. These same settings are used for all samples. At 2700 cm−1 (white regions, Figures 8 and 9), numerous specks are visible in MWCNT-exposed tissues, while the background signal in dispersion media control tissue is minimal. The 2930 cm−1 frequency represents −CH3 symmetric stretch and allows the tissues to be clearly visible (blue regions, Figures 8 and 9). The 2930 cm−1 spectrum corresponding to tissue can be seen in Figure 1(C). In addition to the tissue-only control, a MWCNT-only control was examined to confirm positive signal at 2700 cm−1 and negative signal at 2930 cm−1.