scholarly journals Registration of a laser beam scattered from an aerosol located in the probe beam aperture

2019 ◽  
Author(s):  
Vyacheslav F. Myshkin ◽  
Valeriy A. Khan ◽  
Milan Tichy ◽  
Anna Kapran ◽  
Valentin A. Borisov ◽  
...  
Keyword(s):  
Laser Beam ◽  
Probe Beam ◽  
Beam Aperture

Fluidic Laser Beam Shaper by Using Thermal Lens Effect

2011 ◽  
Author(s):  
Hong Duc Doan ◽  
Yoshihiko Akamine ◽  
Kazuyoshi Fushinobu
Keyword(s):  
Refractive Index ◽  
Pump Power ◽  
Absorption Coefficient ◽  
Laser Beam ◽  
Probe Beam ◽  
Thermal Lens ◽  
Refractive Index Distribution ◽  
Index Distribution ◽  
Thermal Lens Effect ◽  
Flat Top Beam

Laser measurement and laser processing techniques have been gaining strong attention from various applications [1,2]. This research aims at the development of a fluidic laser beam shaper, and in order to fulfill the objective, characteristics of the thermal lens effect are studied. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the liquid is irradiated. One reason for the refractive index distribution in the liquid is the temperature distribution in the liquid when it is irradiated. In this research, effects of the pump power and propagation distance of the probe beam to probe beam profile are investigated experimentally and theoretically, in order to develop fluidic laser beam shaper. It is indicated that, by controlling some parameters in thermal lens system as pump power (in the regime of linear optics) and absorption coefficient, input Gaussian beam can be converted into flat-top beam profile. The relationship among the distance to obtain a flat-top beam, pump power and absorption coefficient is investigated to show the flexibility of fluidic laser beam shaper in many fields of laser application.

Photothermal Reliability Testing of a Multilayer Coating—Substrate Assembly: A Theoretical Approach

1998 ◽  
Vol 120 (1) ◽  
pp. 82-88 ◽  
Author(s):  
T. Elperin ◽  
G. Rudin
Keyword(s):  
Laser Beam ◽  
Probe Beam ◽  
Thermal Stresses ◽  
Deflection Angle ◽  
Multilayer Coating ◽  
Pump Laser ◽  
Reliability Testing ◽  
Fourier Number ◽  
The Deflection Angle ◽  
Pump Laser Beam

The paper presents the theoretical principles underlying the method for photothermal reliability testing of a multilayer coating-substrate assembly. In this method, the assembly is irradiated by the pump laser beam which causes heating and formation of thermal stresses in an assembly. The irradiated surface is monitored by a weak probe beam of another laser to detect the buckling of the coating. The two-dimensional distributions of temperature and thermal stresses in an assembly heated by the pump laser beam are obtained from the solution of the thermal elasticity problem. The developed mathematical procedure is based on the expansion of the Laplace and Hankel transforms of temperature and displacement distributions in series of a small parameter, which is of the order of the ratio of a coating thickness to a pump beam radius. The explicit expressions for the stress tensor components in the layers of a coating and the probe beam deflection angle are derived. Calculations show that the dependence of the deflection angle on a Fourier number is nonmonotone and attains a maximum at some value of the Fourier number. The latter property of the dependence of the deflection angle on the Fourier number can be used for detecting subsurface structural defects in an assembly.

In-Situ Characterization of Thin Polycrystalline Diamond Film Quality by Thermal Wave and Raman Techniques

1989 ◽  
Vol 162 ◽  
Author(s):  
R. W. Pryor ◽  
P. K. Kuo ◽  
L. Wei ◽  
R. L. Thomas ◽  
P. L. Talley
Keyword(s):  
Thermal Conductivity ◽  
Laser Beam ◽  
Probe Beam ◽  
Diamond Film ◽  
Thermal Wave ◽  
Diamond Films ◽  
Film Surface ◽  
Polycrystalline Diamond ◽  
Probe Laser ◽  
Wave Technique

ABSTRACTIn this paper, the thermal wave technique and microfocus Raman spectroscopy are used to measure the relative quality of thin diamond films deposited on silicon. The thermal wave technique uses a modulated heating laser beam, normal to the diamond film surface, to initiate a thermal wave which propagates into the film, the substrate, and the overlying gas(ses). The accompanying modulated gas density is then interrogated by a second (probe) laser beam. The probe beam is deflected by the corresponding periodic changes in the gradient of the refractive index of the gas. The measured probe beam deflection versus offset position is fitted, using a theoretical solution of the three-dimensional thermal diffusion equation for the gas/film/substrate system. The physically important fitting parameter is the thermal diffusivity of the diamond film. Thermal conductivities derived from our diffusivity measurements using this method compare well to previous measurements on similarly prepared films by other methods. Our measured values for the thermal conductivity of the highest-quality polycrystalline diamond films are of the order of 12 W/cm-K. Our measured values of thermal conductivity for diamond films range between this value and the thermal conductivity of graphite. We have also made measurements on bulk diamond using the thermal wave technique, and we obtain a thermal conductivity of 21 W/cm-K, in excellent agreement with values found in the literature. A multi-scan, microfocus ratio of “graphitic” material to diamond material for a relative assessment of film quality.

Two-photon excitation microscopy in cellular biophysics

1995 ◽  
Vol 53 ◽  
pp. 62-63
Author(s):  
David W. Piston ◽  
Brian D. Bennett ◽  
Robert G. Summers
Keyword(s):  
Confocal Microscopy ◽  
Laser Beam ◽  
Duty Cycle ◽  
Excited Electronic State ◽  
Input Power ◽  
Two Photon ◽  
Simultaneous Absorption ◽  
Photon Excitation ◽  
Very High ◽  
Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

The atomic-force microscope and its future in biology

1993 ◽  
Vol 51 ◽  
pp. 704-705
Author(s):  
Jean-Paul Revel
Keyword(s):  
Silicon Nitride ◽  
Laser Beam ◽  
Atomic Force Microscope ◽  
Scanning Tunneling Microscope ◽  
Point Of View ◽  
Scanning Tunneling ◽  
Close Relative ◽  
Tunneling Microscope ◽  
Atomic Force ◽  
Sharp Point

The last few years have been marked by a series of remarkable developments in microscopy. Perhaps the most amazing of these is the growth of microscopies which use devices where the place of the lens has been taken by probes, which record information about the sample and display it in a spatial from the point of view of the context. From the point of view of the biologist one of the most promising of these microscopies without lenses is the scanned force microscope, aka atomic force microscope.This instrument was invented by Binnig, Quate and Gerber and is a close relative of the scanning tunneling microscope. Today's AFMs consist of a cantilever which bears a sharp point at its end. Often this is a silicon nitride pyramid, but there are many variations, the object of which is to make the tip sharper. A laser beam is directed at the back of the cantilever and is reflected into a split, or quadrant photodiode.

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