scholarly journals Enhancement of Photoacoustic Signal Strength with Continuous Wave Optical Pre-Illumination: A Non-Invasive Technique

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1190
Author(s):  
Anjali Thomas ◽  
Souradip Paul ◽  
Joy Mitra ◽  
Mayanglambam Suheshkumar Singh
Keyword(s):  
Methylene Blue ◽  
Continuous Wave ◽  
Optical Power ◽  
Signal Strength ◽  
Optical Beam ◽  
Clinical Translation ◽  
Optical Absorption Coefficient ◽  
Invasive Technique ◽  
Light Sources ◽  
Chicken Tissue

Use of portable and affordable pulse light sources (light emitting diodes (LED) and laser diodes) for tissue illumination offers an opportunity to accelerate the clinical translation of photoacoustic imaging (PAI) technology. However, imaging depth in this case is limited because of low output (optical) power of these light sources. In this work, we developed a noninvasive technique for enhancing strength (amplitude) of photoacoustic (PA) signal. This is a photothermal-based technique in which a continuous wave (CW) optical beam, in addition to short-pulse ~ nsec laser beam, is employed to irradiate and, thus, raise the temperature of sample material selectively over a pre-specified region of interest (we call the process as pre-illumination). The increase in temperature, in turn enhances the PA-signal strength. Experiments were conducted in methylene blue, which is one of the commonly used contrast agents in laboratory research studies, to validate change in temperature and subsequent enhancement of PA-signal strength for the following cases: (1) concentration or optical absorption coefficient of sample, (2) optical power of CW-optical beam, and (3) time duration of pre-illumination. A theoretical hypothesis, being validated by numerical simulation, is presented. To validate the proposed technique for clinical and/or pre-clinical applications (diagnosis and treatments of cancer, pressure ulcers, and minimally invasive procedures including vascular access and fetal surgery), experiments were conducted in tissue-mimicking Agar phantom and ex-vivo animal tissue (chicken breast). Results demonstrate that pre-illumination significantly enhances PA-signal strength (up to ~70% (methylene blue), ~48% (Agar phantom), and ~40% (chicken tissue)). The proposed technique addresses one of the primary challenges in the clinical translation of LED-based PAI systems (more specifically, to obtain a detectable PA-signal from deep-seated tissue targets).

A spaceborne neodymium-doped yttrium aluminum garnet laser with nonplanar-ring-oscillator configuration

2021 ◽  
pp. 2140007
Author(s):  
Jiankang Peng ◽  
Liufeng Li ◽  
Lisheng Chen ◽  
Keyword(s):  
Yttrium Aluminum Garnet ◽  
Continuous Wave ◽  
Optical Power ◽  
Ring Oscillator ◽  
Light Sources ◽  
Design Development ◽  
Space Applications ◽  
Yttrium Aluminum ◽  
Environmental Test ◽  
One Year

Due to their excellent noise performance and technical maturity, ultra-stable continuous-wave neodymium-doped yttrium aluminum garnet lasers are one of the major light sources in a series of precision measurements such as ground and space-based gravitational wave detection, inter-satellite laser ranging and coherent optical communication. As the first step of developing an ultra-stable spaceborne laser, we carried out the design, development and environmental test of an all-solid-state Nd:YAG NPRO spaceborne laser. The laser deliveries 11.48 mW of optical power at 1064.405 nm, exhibits intensity and frequency noises less than 1 × 10[Formula: see text]/[Formula: see text]Hz and 1 MHz/[Formula: see text]Hz (Fourier frequencies ¿ 10 mHz), respectively, passed environmental tests and has been onboard the first satellite of the Taiji program for one year. The work laid a solid foundation for realizing ultra-stable lasers for the Taiji program as well as being used in many space applications.

scholarly journals A Passively Q-Switched Holmium-Doped Fiber Laser with Graphene Oxide at 2058 nm

2021 ◽  
Vol 11 (1) ◽  
pp. 407
Author(s):  
Jinho Lee ◽  
Ju Han Lee
Keyword(s):  
Graphene Oxide ◽  
Pump Power ◽  
Fiber Laser ◽  
Ring Resonator ◽  
Continuous Wave ◽  
Optical Power ◽  
Polished Surface ◽  
Fiber Ring ◽  
Q Switching ◽  
Side Polished Fiber

This study reports a Q-switching-based, 2058-nm holmium (Ho) fiber laser incorporating a saturable absorber (SA) based on graphene oxide (GO). The SA was prepared with a side-polished fiber, while GO particles were deposited onto the fiber-polished surface to realize an all-fiber SA. A continuous-wave thulium-doped all-fiber laser, which was configured with a master-oscillator power-amplifier (MOPA) structure, was constructed as a pumping source. By inserting the fabricated SA into an all-fiber ring resonator based on 1-m length of Ho-doped fiber, Q-switched pulses could readily be obtained at a wavelength of 2058 nm. The pulse width was observed to vary from 2.01 to 1.56 μs as the pump power was adjusted from ~759 to 1072 mW, while the repetition rate was tunable from 45.56 to 56.12 kHz. The maximum values of average optical power and pulse energy were measured as ~11.61 mW and 207.05 nJ, respectively, at a ~1072 mW pump power.

scholarly journals Photon counting statistics with imperfect detectors

2021 ◽  
Vol 2086 (1) ◽  
pp. 012096
Author(s):  
Aleksei Reutov ◽  
Denis Sych
Keyword(s):  
Continuous Wave ◽  
Single Photon ◽  
Functional Dependence ◽  
Photon Counting ◽  
Light Sources ◽  
Photon Detectors ◽  
Quantum Properties ◽  
Single Photon Detectors ◽  
The Mean ◽  
Counting Statistics

Abstract Measurement of photon statistics is an important tool for the verification of quantum properties of light. Due to the various imperfections of real single photon detectors, the observed statistics of photon counts deviates from the underlying statistics of photons. Here we analyze statistical properties of coherent states, and investigate a connection between Poissonian distribution of photons and sub-Poissonian distribution of photon counts due to the detector dead-time corrections. We derive a functional dependence between the mean number of photons and the mean number of photon counts, as well as connection between higher-order statistical moments, for the pulsed or continuous wave coherent light sources, and confirm the results by numerical simulations.

scholarly journals Dynamics of microresonator frequency comb generation: models and stability

Nanophotonics ◽  
2016 ◽  
Vol 5 (2) ◽  
pp. 231-243 ◽  
Author(s):  
Tobias Hansson ◽  
Stefan Wabnitz
Keyword(s):  
Continuous Wave ◽  
Temporal Dynamics ◽  
Frequency Comb ◽  
Modulational Instability ◽  
Theoretical Models ◽  
Light Sources ◽  
Generation Process ◽  
Modal Expansion ◽  
Frequency Combs ◽  
Comb Generation

AbstractMicroresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

scholarly journals Ultrafast electro-optic light with subcycle control

Science ◽  
2018 ◽  
Vol 361 (6409) ◽  
pp. 1358-1363 ◽  
Author(s):  
David R. Carlson ◽  
Daniel D. Hickstein ◽  
Wei Zhang ◽  
Andrew J. Metcalf ◽  
Franklyn Quinlan ◽  
...  
Keyword(s):  
High Speed ◽  
Near Infrared ◽  
Continuous Wave ◽  
Mode Locking ◽  
Light Sources ◽  
Electro Optic ◽  
High Pulse ◽  
Optical Cycle ◽  
Rapid Transients ◽  
And Control

Light sources that are ultrafast and ultrastable enable applications like timing with subfemtosecond precision and control of quantum and classical systems. Mode-locked lasers have often given access to this regime, by using their high pulse energies. We demonstrate an adaptable method for ultrastable control of low-energy femtosecond pulses based on common electro-optic modulation of a continuous-wave laser light source. We show that we can obtain 100-picojoule pulse trains at rates up to 30 gigahertz and demonstrate sub–optical cycle timing precision and useful output spectra spanning the near infrared. Our source enters the few-cycle ultrafast regime without mode locking, and its high speed provides access to nonlinear measurements and rapid transients.

scholarly journals Coherent Ray Tracing Simulation Of Non-Imaging Laser Beam Shaping With Multi-Aperture Elements

2019 ◽  
Vol 215 ◽  
pp. 01001
Author(s):  
Raoul Kirner ◽  
Wilfried Noell ◽  
Toralf Scharf ◽  
Reinhard Voelkel
Keyword(s):  
Ray Tracing ◽  
Continuous Wave ◽  
Laser Light ◽  
Traditional Approach ◽  
Statistical Treatment ◽  
Diffraction Theory ◽  
Beam Shaping ◽  
Optical Systems ◽  
Light Sources ◽  
Mask Aligner

The application of laser light sources for illumination tasks like in mask aligner lithography relies on non-imaging optical systems with multi-aperture elements for beam shaping. When simulating such systems, the traditional approach is to separate the beam-shaping part (incoherent simulation) from dealing with coherence properties of the illuminating laser light source (diffraction theory with statistical treatment). We present an approach using Gaussian beam decomposition to include coherence simulation into ray tracing, combining these two parts, to get a complete picture in one simulation. We discuss source definition for such simulations, and verify our assumptions on a well-known system. We then apply our approach to an imaging beam shaping setup with microoptical multi-aperture elements. We compare the simulation to measurements of a similar beam-shaping setup with a 193 nm continuous-wave laser in a mask-aligner configuration.

scholarly journals Multivariate Analysis of Photoacoustic Spectra for the Detection of Short-Chained Hydrocarbon Isotopologues

Molecules ◽  
2020 ◽  
Vol 25 (9) ◽  
pp. 2266 ◽  
Author(s):  
Alain Loh ◽  
Marcus Wolff
Keyword(s):  
Multivariate Analysis ◽  
Continuous Wave ◽  
Light Sources ◽  
Least Squares Regression ◽  
Detection Scheme ◽  
Concentration Determination ◽  
Multiple Measurements ◽  
Interband Cascade Lasers ◽  
Cascade Lasers

We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, served as light sources. The investigations comprised the main stable carbon isotopologues of methane (12CH4, 13CH4), ethane (12CH3-12CH3, 13CH3-12CH3, 13CH3-13CH3), and propane (12CH3-12CH2-12CH3, 13CH3-12CH2-12CH3). They were selected because of their importance for numerous applications from climate and planetary research to natural gas exploration. Multiple measurements of single components in nitrogen and synthetic mixtures were conducted at room temperature and atmospheric pressure. Depending on the investigated hydrocarbon isotopologue, detection limits ranging from 0.043 ppmv to 3.4 ppmv were achieved. For a selective concentration determination, multivariate analysis (MVA) was applied. Partial least-squares regression (PLSR) was used to calculate concentrations from the PA spectra. The implementation of MVA has shown that the PA setup in principle works reliably and that the selective concentration determination of short-chained hydrocarbon isotopologues is possible.

scholarly journals Recent Advances in Aerosol and Trace Gas Monitoring by Employing the Scheimpflug Lidar Techniques

2020 ◽  
Vol 237 ◽  
pp. 07022
Author(s):  
Liang Mei ◽  
Zheng Kong ◽  
Teng Ma ◽  
Zhi Liu ◽  
Zhenfeng Gong ◽  
...  
Keyword(s):  
Continuous Wave ◽  
Laser Diodes ◽  
Image Sensor ◽  
Trace Gas ◽  
Light Sources ◽  
Continuous Wave Laser ◽  
Gas Monitoring ◽  
Power Laser ◽  
Recent Advances ◽  
Atmospheric Remote Sensing

Lidar techniques, based on the time-of-flight principle, have been widely employed in atmospheric remote sensing since decades. The Scheimpflug lidar (SLidar) technique, which employing robust high-power laser diodes as light sources and highly integrated CCD/CMOS image sensor as detectors, has been recently developed for various atmospheric applications. Range-resolved atmospheric backscattering signal is obtained by capturing the backscattering imaging of transmitted continuous-wave laser beam based on the Scheimpflug principle. This paper reported recent advances in aerosol and trace gas monitoring by employing the SLidar techniques.

Accelerator-based X-ray sources: synchrotron radiation, X-ray free electron lasers and beyond

2019 ◽  
Vol 377 (2147) ◽  
pp. 20180231 ◽  
Author(s):  
Tetsuya Ishikawa
Keyword(s):  
Synchrotron Radiation ◽  
Storage Ring ◽  
Free Electron ◽  
Continuous Wave ◽  
Transitional Period ◽  
Light Sources ◽  
X Rays ◽  
Free Electron Lasers ◽  
Beam Emittance ◽  
X Ray

The evolution of synchrotron radiation (SR) sources and related sciences is discussed to explain the ‘generation’ of the SR sources. Most of the contemporary SR sources belong to the third generation, where the storage rings are optimized for the use of undulator radiation. The undulator development allowed to reduction of the electron energy of the storage ring necessary for delivering 10 keV X-rays from the initial 6–8 GeV to the current 3 Gev. Now is the transitional period from the double-bend-achromat lattice-based storage ring to the multi-bend-achromat lattice to achieve much smaller electron beam emittance. Free electron lasers are the other important accelerator-based light sources which recently reached hard X-ray regime by using self-amplified spontaneous emission scheme. Future accelerator-based X-ray sources should be continuous wave X-ray free electron lasers and pulsed X-ray free electron lasers. Some pathways to reach the future case are discussed. This article is part of the theme issue ‘Fifty years of synchrotron science: achievements and opportunities’.

scholarly journals High Photocurrent Density and Continuous Electron Emission Characterization of a Multi-Alkali Antimonide Photocathode

Electronics ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 1991
Author(s):  
Jun Dai ◽  
Yikun Ding ◽  
Cunjun Ruan ◽  
Xiangyan Xu ◽  
Hulin Liu
Keyword(s):  
Electric Fields ◽  
Current Density ◽  
Electron Emission ◽  
Continuous Wave ◽  
High Current Density ◽  
Optical Power ◽  
Photocurrent Density ◽  
Maximum Current ◽  
Section Electron

High photocurrent density cathodes that enable small cross-section electron beams are required for high-power terahertz vacuum devices. Multi-alkali antimonide photocathodes may be well suited for generating sub-mm electron beam sources. This paper involves the repeatability, stability, uniformity, and linearity experiments of the multi-alkali antimonide photocathodes electron emission operations under a continuous-wave 450 nm laser with a bias voltage of 5000 V. The effect of heat, electric contact, and cathode surface roughness to emission characterizations is analyzed. The methods to maintain the high-current-density emission and avoid the fatigue of the photocathode are verified. The emission can be repeated with increased optical power. The stable photocurrent density of near 1 A/cm2 and maximum current density of near 1.43 A/cm2 is recorded. The continuous photocurrent density is significantly improved compared to the current density reported in traditional applications. It is found that the current curves measuring at different areas of the photocathode differ greatly after the laser power of 800 mW. The increase in current for some areas may be attributed to the conductive current caused by built-in electric fields between the emission rough area and its adjacent areas.

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