Entropy and Efficiency in Laser Cooling of Solids

2007 ◽  
Author(s):  
Xiulin Ruan ◽  
Stephen C. Rand ◽  
Massoud Kaviany
Keyword(s):  
Laser Cooling ◽  
Laser Action ◽  
Blackbody Radiation ◽  
Stimulated Emission ◽  
Light Sources ◽  
Photon Distribution ◽  
Random Lasers ◽  
Emission Process ◽  
Wide Range ◽  
Radiation Entropy

The thermodynamics of laser cooling of solids is analyzed. Using the general theory of radiation entropy, the important roles of the optical frequency and the photon distribution function in determining the radiation entropy are identified. The usefulness of a narrowband approximation is established for a wide range of radiant sources. This approximation is then applied to compare the entropies of different light sources, including blackbody radiation, lasers, fluorescence, and the emerging class of random lasers. Based on these results, the Carnot efficiency for laser cooling of solids is determined, for emission fields with various entropy characteristics. It is shown that fluorescent emission is the most efficient form of the radiated field for laser cooling of solids, and cooling schemes based on any stimulated emission process (including random laser action) are inherently less efficient. The influence of luminescence quantum yield on cooling is also considered.

scholarly journals Progresses on the Use of Two-Photon Absorption Laser Induced Fluorescence (TALIF) Diagnostics for Measuring Absolute Atomic Densities in Plasmas and Flames

Plasma ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 145-171
Author(s):  
Kristaq Gazeli ◽  
Guillaume Lombardi ◽  
Xavier Aubert ◽  
Corinne Y. Duluard ◽  
Swaminathan Prasanna ◽  
...  
Keyword(s):  
Optical Transition ◽  
Thin Film Deposition ◽  
Laser Induced Fluorescence ◽  
Film Deposition ◽  
Stimulated Emission ◽  
Photon Absorption ◽  
Collisional Quenching ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Wide Range

Recent developments in plasma science and technology have opened new areas of research both for fundamental purposes (e.g., description of key physical phenomena involved in laboratory plasmas) and novel applications (material synthesis, microelectronics, thin film deposition, biomedicine, environment, flow control, to name a few). With the increasing availability of advanced optical diagnostics (fast framing imaging, gas flow visualization, emission/absorption spectroscopy, etc.), a better understanding of the physicochemical processes taking place in different electrical discharges has been achieved. In this direction, the implementation of fast (ns) and ultrafast (ps and fs) lasers has been essential for the precise determination of the electron density and temperature, the axial and radial gradients of electric fields, the gas temperature, and the absolute density of ground-state reactive atoms and molecules in non-equilibrium plasmas. For those species, the use of laser-based spectroscopy has led to their in situ quantification with high temporal and spatial resolution, with excellent sensitivity. The present review is dedicated to the advances of two-photon absorption laser induced fluorescence (TALIF) techniques for the measurement of reactive species densities (particularly atoms such as N, H and O) in a wide range of pressures in plasmas and flames. The requirements for the appropriate implementation of TALIF techniques as well as their fundamental principles are presented based on representative published works. The limitations on the density determination imposed by different factors are also discussed. These may refer to the increasing pressure of the probed medium (leading to a significant collisional quenching of excited states), and other issues originating in the high instantaneous power density of the lasers used (such as photodissociation, amplified stimulated emission, and photoionization, resulting to the saturation of the optical transition of interest).

scholarly journals Effect of light on aggregational behavior of planarian Dugesia tigrina

2017 ◽  
Author(s):  
Jaemin Lee
Keyword(s):  
Defense Mechanisms ◽  
Uv Light ◽  
Infrared Light ◽  
Light Sources ◽  
Initial Exposure ◽  
Dugesia Tigrina ◽  
Wide Range ◽  
Photophobic Response ◽  
Negative Effect ◽  
Effect Of Light

Introduction. Planarians are renowned for their regenerative ability due to pluripotent stem cells, as well as their peculiar photophobic response. However, few facts are known about their aggregational behavior. This study aims to reveal the effect of light on aggregational behavior. Reynierse (1966) suggested that light has a negative effect on the formation of aggregations. However, one of his objectives for aggregational behavior was inappropriate. This study reevaluated the effect of existence of light on aggregational behavior, as well as ascertained the effect of wavelength on the formation of aggregations. Methods. In this study, the ratio of individuals participating in aggregations was measured as a criterion to determine aggregational behavior. Aggregational behavior was measured after two hours from the initial exposure to different light sources. The behaviors under white LED light and under shade were compared, as well as the behaviors under five different light sources: infrared lamp, red, green, blue LED, and ultraviolet lamp. Results. The existence of light interfered the formation of aggregations (t-test, p < 0.0001), which supports the former study of Reynierse. Also, aggregational behavior differed under different wavelengths (ANOVA, p < 0.0001). Except for the infrared light which emitted a wide range of wavelengths, the behavior showed hierarchy: decreasing aggregational behavior in accordance with decreasing wavelength. UV light has the most significant negative effect on the formation of aggregations. Discussion. Exposure to light caused negative effects on performing aggregational behavior. Participation in aggregations appears to be influenced by photophobic response, especially under lights of short wavelength. Disintegrating aggregations under exposure to lights can potentially bring evolutionary benefit. This behavior possibly makes the aggregating planarians altogether exposed to a higher risk or predation, considering that they lack defense mechanisms. Planarians can lower the risk and continue the populations by disintegrating the aggregational behavior under the existence of UV and lights of higher wavelength, which are indicatives of daytime. Understanding aggregational behavior of animals of a lower order would give better insight on general herding behavior, and potentially help interpreting more complex behaviors of higher animals.

An Optical Instrument for Measuring Fluctuating Velocities in Highly Turbulent Flows

1978 ◽  
Vol 29 (2) ◽  
pp. 98-113 ◽  
Author(s):  
M. Gaster ◽  
J.F.M. Maybrey
Keyword(s):  
Turbulent Flows ◽  
Light Sources ◽  
Optical Instrument ◽  
Surface Reflection ◽  
Power Spectral ◽  
Optical Layout ◽  
Wide Range ◽  
Laser Anemometer ◽  
Sampling Zone ◽  
Highly Turbulent Flows

SummaryFlow measurement by optical devices of various types, particularly those involving laser light sources, have received considerable attention over the last few years. Different schemes employing a wide range of optical layouts have evolved and the resulting signals have been processed in a number of ingenious ways. We report new experimental work on an optical instrument that can be considered as the forerunner of the laser anemometer in the belief that in certain circumstances this particular optical layout offers some real advantages over the majority of laser anemometers. One important advantage of this system is the ease with which both the shape and size of the sampling zone can be independently controlled. Another is the ability to position the sampling region very close to a boundary without having to contend with the surface reflection difficulties that often prevent such measurements being made with laser optics. The instrument measures the velocities of small particles suspended in the fluid in much the same way as the laser anemometer. In unsteady flows this results in a series of velocity estimates generated at random time instants. These intermittent samples of the velocity are used to form power spectral density estimates by methods recently developed for the analysis of randomly sampled records (Gaster and Roberts, 1975 & 1976). This method of analysis could well be applied to the processing of the signals generated by laser anemometers operating in the burst counter mode.

Onset Times and Detection of Colored Signal Lights

2005 ◽  
Vol 1918 (1) ◽  
pp. 123-127
Author(s):  
John D. Bullough
Keyword(s):  
Visual Detection ◽  
Practical Significance ◽  
Light Sources ◽  
Significant Potential ◽  
Color Characteristics ◽  
Signal Light ◽  
Wide Range ◽  
The Impact ◽  
Transportation Applications ◽  
Selection Of

Light sources used in signal lights for transportation applications have a variety of temporal onset characteristics, including a wide range of onset times. These characteristics, along with luminous intensity and color characteristics, can have important impacts on the ability to detect and respond to colored signal lights. Studies of the impact of these factors on responses to colored signals are reviewed, along with potential implications for the selection of light sources used in traffic and vehicle signals. The onset characteristics of recently developed light sources might offer significant potential to improve visual detection of signal lights. Nonetheless, it is important to understand the context in which a signal light is presented to determine whether such improvements in visual detection have practical significance.

scholarly journals Optically Pumped Intensive Light Amplification from a Blue Oligomer

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1534 ◽  
Author(s):  
Aljaafreh ◽  
Prasad ◽  
AlSalhi ◽  
Alahmed ◽  
M. Al-Mogren
Keyword(s):  
Self Assembly ◽  
High Efficiency ◽  
Laser Action ◽  
Pump Energy ◽  
Optically Pumped ◽  
Time Resolved ◽  
Protic Solvents ◽  
Light Amplification ◽  
Wide Range ◽  
The Fourier Transform

We demonstrated the time-resolved dynamics of laser action from the conductive oligomer (CO) 1,4-Bis(9-ethyl-3-carbazo-vinylene)-9,9-dihexyl-fluorene (BECV-DHF). Absorption and fluorescence spectra were studied for BECV-DHF in different solvents under a wide range of concentrations. The Fourier-transform infrared spectroscopy (FTIR) spectrum was measured using simulation and experiments. The Ultraviolet-Visible (UV-VIS) spectra of the BECV-DHF were simulated in two different solutions. This CO formed a dimer and had two vibration bands in nonpolar solvents, partially dissolved in polar protic solvents, and created an H-type aggregate in polar aprotic solvents. BECV-DHF produced amplified spontaneous emission (ASE) at 464 nm in many solvents. The high efficiency of ASE is due to the waveguiding and self-assembly nature of the oligomer, which is very rare for optically pumped systems. However, BECV-DHF did not produce ASE in polar protic solvents. BECV-DHF produced ASE in both longitudinal and transverse pumping, and the full-width half maximum (FWHM) was 4 nm and 8 nm respectively for different solvents, such as toluene and acetone. The CO had a very low threshold pump energy (~0.5 mJ). The ASE efficiency was approximately 20%. The time-resolved spectroscopy (TRS) studies showed a temporal Gaussian-shaped ASE output from this CO. BECV-DHF shows remarkably high stability compare to the conjugated polymer (CP) PFO-co-pX.

Experimentelle Untersuchungen zur Stark-Verbreiterung der Balmer-Linien Hα und Hβ / Experimental Investigation of the Stark Broadening of the Balmer Lines Hα and Hβ

1973 ◽  
Vol 28 (11) ◽  
pp. 1794-1800 ◽  
Author(s):  
Horst Ehrich ◽  
Hans Jürgen Kusch
Keyword(s):  
Electron Density ◽  
Plasma Temperature ◽  
Light Sources ◽  
Stark Broadening ◽  
Pulsed Discharge ◽  
Empirical Correction ◽  
Wide Range ◽  
Balmer Lines ◽  
Empirical Correction Factor ◽  
Density Scale

The profiles of the Stark broadened Balmer lines Hα and Hβ have been measured in a wide range of temperature and electron density. By the use of different light sources (3 wallstabilized arcs of different design, a pulsed discharge tube and a plexiglass-capillary discharge) the range was ex- tended to 1.0·104≦T≦3.2·104 °K for the plasma temperature and to 1·1016≦ne≦55·1016 cm−3 for the electron density in the Hβ-scale. The experimental profiles of the Hα-line agree with generalized impact approximations if the condition: ne2/3/T>2·107 cm−2 grad−1 is fulfilled. Disagreements between the Hα and Hβ electron density scale can be removed applying an empirical correction-factor to the electron density obtained from the half-width of Hα.

Stimulated emission of Ho3+ and Er3+ ions in Gd3Ga5O12 crystals and cascade laser action of Ho3+ ions over the5S2 →5I5 →5I6 →5I8 scheme

1979 ◽  
Vol 53 (2) ◽  
pp. K219-K222 ◽  
Author(s):  
A. A. Kaminskii ◽  
V. A. Fedorov ◽  
S. E. Sarkisov ◽  
J. Bohm ◽  
P. Reiche ◽  
...  
Keyword(s):  
Laser Action ◽  
Stimulated Emission

scholarly journals X-ray detectors at the Linac Coherent Light Source

2015 ◽  
Vol 22 (3) ◽  
pp. 577-583 ◽  
Author(s):  
Gabriel Blaj ◽  
Pietro Caragiulo ◽  
Gabriella Carini ◽  
Sebastian Carron ◽  
Angelo Dragone ◽  
...  
Keyword(s):  
Light Source ◽  
Light Sources ◽  
Coherent Light ◽  
X Ray ◽  
Wide Range ◽  
Linac Coherent Light Source ◽  
Design Requirements ◽  
New Generation ◽  
Coherent Light Source ◽  
Detector Design

Free-electron lasers (FELs) present new challenges for camera development compared with conventional light sources. At SLAC a variety of technologies are being used to match the demands of the Linac Coherent Light Source (LCLS) and to support a wide range of scientific applications. In this paper an overview of X-ray detector design requirements at FELs is presented and the various cameras in use at SLAC are described for the benefit of users planning experiments or analysts looking at data. Features and operation of the CSPAD camera, which is currently deployed at LCLS, are discussed, and the ePix family, a new generation of cameras under development at SLAC, is introduced.

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