Observation of resonances at subharmonics of the Rabi frequency in the saturated absorption of a 100% amplitude-modulated laser beam

The Cs(7P)+H2→CsH+H reaction is studied in a crossed-beam experiment with laser-induced fluorescence detection of CsH products. The usual flux (≈50mW/mm2) which is delivered by the C.W. tunable dye laser used in the experiment is enough to saturate the absorption by CsH products. Then, by crossing twice the laser beam through the collision volume (counterpropagating beams), one realizes the conditions of saturated-absorption experiments: when the laser frequency is tuned to a resonance frequency of CsH products, a defect to absorption occurs for these products which scatter in the collision plane and a "saturation dip" appears at the center of the corresponding fluorescence profile. Application of this technique to crossed-beam experiments can lead to the selection of product molecules which scatter in any definite plane. A different geometry of the laser beams (bent beams) is proposed to select molecules which scatter in any definite direction: it could be applied to detect an asymmetry in the scattering of the products with respect to the collision axis, when a particular preparation of the reagents is realized.

Download Full-text

Effect of Laser Beam Diameter Variation in Saturated Absorption Spectra

Journal of the Physical Society of Japan ◽

10.1143/jpsj.77.074301 ◽

2008 ◽

Vol 77 (7) ◽

pp. 074301 ◽

Cited By ~ 6

Author(s):

Geol Moon ◽

Heung-Sik Noh ◽

Heung-Ryoul Noh

Keyword(s):

Laser Beam ◽

Absorption Spectra ◽

Beam Diameter ◽

Laser Beam Diameter ◽

Saturated Absorption ◽

Diameter Variation

Download Full-text

Two-photon excitation microscopy in cellular biophysics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136684 ◽

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.

Download Full-text

The atomic-force microscope and its future in biology

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149350 ◽

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.

Download Full-text