Jeffrey Y. Tsao

The origin of the infrared multiphoton induced luminescence of chromyl chloride

We have studied systematically the luminescence induced when CrO2Cl2 is infrared multiphoton excited by a moderate fluence (0–15 J/cm2) CO2 laser. This includes the dependence of the full luminescence spectrum on CO2 laser fluence, and for various spectral regions of the luminescence their dependence on CO2 laser wavelength and fluence, their intramolecular decay rates, and using a time‐of‐flight technique the translational temperatures associated with their sources. These measurements show that two species contribute to the luminescence. In addition, a chemical identification of these species is made by preceding the IR laser pulse with a UV laser pulse to photochemically prepare the CrO2Cl fragment, and isolate its contribution to the luminescence. Strong evidence is obtained in support of both CrO2Cl fragment and CrO2Cl2 parent contributions to the luminescence. The relative contributions of the two to the luminescence and an absolute yield for the IR multiphoton induced dissociation of CrO2Cl2 into Cr...

Multiphoton vibrational pumping on optically prepared NO2 molecules

Abstract Reported is the collisionless infrared multiphoton excitation of NO2 molecules initially prepared in an electronically excited state. From the shape of the infrared induced blue-shifted fluorescence spectrum the probability distribution P(n) for the net absorption of n photons has been deduced.

Laser‐Controlled Wet Chemical Etching for Corrective Trimming of Thin Films Application to Aluminum

The localized enhancement of wet chemical etching by focused laser beams for corrective trimming of thin films, and its application to the selective etching of aluminum, are discussed. Since wet etching can proceed rapidly even without irradiation, it is as important to consider methods for reducing background etching as to consider those for enhancing localized etching. The process developed for aluminum etching is based upon moderate local heating to activate a reaction that is normally suppressed by a corrosion inhibitor. Another approach to the reduction of background etching is solution cooling: for the activation energies for typical wet etching, it should be possible to obtain acceptable contrast ratios between laser-enhanced and background rates over the temperature range within which many concentrated etching solutions are liquid.

Observation of direct infrared multiphoton pumping of the triplet manifold of biacetyl

Direct collisionless multiphoton (MP) excitation of the triplet vibronic manifold of biacetyl is reported. Following a dye laser pulse which prepares some of the biacetyl molecules in the triplet metastable state, the system is irradiated by an intense 20 ns 9.6μ CO2 pulse. The CO2 radiation induces fast quenching of the phosphorescence emission from the 3Au excited molecules. It also induces an emission signal in the fluorescence spectral region of biacetyl. This signal is related to an inverse electronic relaxation (IER) from excited triplet vibronic levels into isoenergetic singlet 1Au vibronic levels. Analysis of the induced luminescence signals provides information on the collisionless MP prompted vibrational distribution. Excitation with 10.6μ CO2 pulses leads to the simultaneous MP pumping of both the ground and triplet manifolds. The generation of blue emission signals in this experiment bears a close resemblance to recent observations of prompt visible emission due to MP pumping of ground state m...

Emitter lifetime and velocity distribution in the collisionless IR multiphoton excitation of chromyl chloride

Abstract The collisionless infrared multiphoton exeitation of chromyl chlonde is studied systematically. An attempt is made to find the parentage of the induced visible emission.

The dynamics of the infrared multiphoton pumping of optically excited NO2 molecules

The infrared multiphoton (IRMP) pumping of optically excited NO2 molecules is investigated. From changes in the fluorescence emission spectrum due to the IRMP pumping, both the fraction of the NO2 molecules that has dissociated, as well as the fraction that remains within one IR photon in energy below the dissociation limit, are deduced. This has made possible the first direct measurements of the final, dissociative step in the IRMP pumping of molecules, and of IRMP stimulated emission. The dynamics of the IRMP pumping is studied by systematically varying the optical excitation energy. The results are compared with numerical solutions to the well‐known rate equation model for the IRMP pumping of polyatomic molecules. From this comparison the best fit transition cross sections connecting various energy regions in highly vibrationally excited NO2 molecules were deduced. Except for the final, dissociative transition, they depend significantly on both laser intensity and pulse width for intensities as large a...

Digital feedback stabilization of a single‐axial‐mode CO2 TEA laser

We have achieved long-term stability in producing high-power single-axial-mode CO2 laser pulses with a hybrid oscillator (TEA laser + low-pressure section) by using a novel digital feedback system that electronically adjusts cavity length.

MULTIPHOTON VIBRATIONAL PUMPING OF OPTICALLY PREPARED NO2 MOLECULES

We report the collisionless infrared multiphoton excitation of NO2 molecules initially prepared in an electronically excited state. The infrared light induces a blue wing on the usual Stokes-shifted fluorescence spectrum. From the shape of the infrared induced fluorescence spectrum we have directly directly determined the absolute probability distribution P(n) for the net absorption of n photons.