摘要:

Laser spectroscopy greatly facilitates probing condensed‐phase structure and reactivity, particularly in the nanoliter volume of diamond‐anvil high pressure cells. Vibrational frequency shifts and line broadening induced by pressure reveal distinctive contributions from repulsive and attractive solute‐solvent forces. Illustrative data and analysis are presented for iodine, pyridine, and other solutes in benign solvents. In the liquid range, typically extending up to 10–12 kbar, bond length changes are usually only of the order 0.02%; thus molecules are only slightly distorted and a perturbation treatment is appropriate. For quasidiatomic modes, several observed features are consistent with model calculations employing approximations familiar for gas‐phase vibration‐to‐translation energy transfer. At higher pressures, typically in the solid phase above 30 kbar, chemical bonds begin to weaken due to repulsions caused by overlap of electron clouds of neighboring molecules. High pressure thus acts like a catalyst in promoting chemical reactions at low temperatures.

ISSN:0094-243X    

DOI:10.1063/1.37324

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Application of the method of molecular beam photofragmentation translational spectroscopy to the investigation of primary photo‐chemical processes of polyatomic molecules will be the main theme of this lecture. Concerted unimolecular dissociation processes, especially those that dissociate simultaneously into three products will be given as examples to illustrate how information concerning the dynamics and mechanism dissociation processes can be obtained from precise measurements of angular and velocity distributions of products in an experiment in which a well defined beam of molecules is crossed with a laser. Recent studies on the primary and secondary decompositions of RDX is shown to be dominated by concerted dissociation processes.

ISSN:0094-243X    

DOI:10.1063/1.37435

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Recent work, performed in this laboratory, on the effects of mid‐uv radiation in giving rise to single‐photon photo‐excitation of adsorbates will be reviewed. Adsorbates included CH3Br1, H2S1,2and OCS, at sub‐monolayer coverage on clean LiF(001) crystals at 115K in UHV. The surface was irradiated by pulsed excimer radiation, principally at 193, 222 and 308 nm, photo‐fragments and parent molecules leaving the surface energy distribution by time‐of‐flight mass spectrometry. The effects identified include photo‐fragmentation of molecules held at the surface with resultant modified molecular dynamics and cross section, surface aligned photo‐reaction (SAP) between co‐adsorbed species, as well as, photo‐desorption (detachment of slow‐moving parent molecules) and photo‐ejection (detachment of fast‐moving parent molecules). Mechanisms and implications of some of these novel processes will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.37405

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Major advances in solid state laser technology historically have been preceded by advances in pumping technology. The helical lamp used to pump the early ruby lasers was superseded by the linear flashlamp now used to pump Nd:YAG lasers. The next advance in pumping technology is the diode laser array. The improvements in power and efficiency of the diode laser coupled with the fortuitous spectral overlap of the diode laser emission wavelength with the Nd ion absorption bands near 805 nm have led to a revolution in solid state laser capability. Progress has been rapid with new ions and wavelengths reported in the near infrared from 946 nm to 2010 nm. Frequency extension via nonlinear interactions has led to green and blue sources of coherent radiation. Linewidths of less than 10 kHz have been demonstrated. Overall electrical efficiencies of greater than 10% have been achieved. As diode laser sources decrease in cost, high average power diode laser pumped solid state laser sources will become available. Power levels exceeding 1 kW appear possible. Potential applications of these compact all solid state laser sources to spectroscopy, quantum noise limited sensors, astronomy, and materials processing will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.37513

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Tunable and coherent vacuum ultraviolet radiation is now available over broad regions from 200 to ∼60 nm. It is generated by third harmonic and four‐wave frequency mixing in gases and metal vapors, and is of sufficient intensity for absorption and fluorescence spectroscopy. We have recently applied these sources to studies of Xe2, Kr2, and Ar2produced by supersonic jet expansion. Vibronic spectra of Xe2and rovibronic spectra of Kr2and Ar2arising from transitions between the ground and three lowest (stable) excited states have been recorded at resolving powers of 1 − 5×105. Spectroscopic constants have been derived, potential energy curves computed, and radiative lifetimes measured and compared with theory.

ISSN:0094-243X    

DOI:10.1063/1.37484

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Upconversion pumping with near‐infrared cw dye lasers was used to achieve laser action at 550 nm on the4S3/2→4I15/2transition of Er3+. In YAlO3:Er3+, upconversion excitation occurs via sequential two‐photon absorption. In YLiF4:Er3+, energy transfer upconversion involving two Er3+ions in the intermediate4I11/2state causes excitation of the upper laser level. These upconversion lasers operate at temperatures up to 90 K. With pump powers of several hundred milliwatt near 800 nm we have obtained 550‐nm output powers in the miliwatt range.

ISSN:0094-243X    

DOI:10.1063/1.37522

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have developed a model of an end‐pumped, injection seeded Titanium doped Sapphire ring laser. The model of the active region has two primary ingredients—continuity equations describing the temporal development of the right and left traveling waves through the medium and a set of rate equations describing the evolution of the electron population in a four level model of the vibronically broadened transitions between levels of the Titanium ion. The model describes the spatial‐temporal behavior of the photon flux within the cavity. We report here on the effects of a reverse wave suppressor mirror on the onset of lasing.

ISSN:0094-243X    

DOI:10.1063/1.37378

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Performance data for a laser diode pumped cw Nd:BEL laser is presented. Two phased laser diode arrays are used as the pump source, each emitting 500 mW. The heat sink for the arrays is temperature controlled to allow for wavelength tunability. A Nd:YAG rod was pumped under similar conditions and the results are compared. Although the absorption bandwidth for Nd:BEL is substantially broader than for Nd:YAG the Nd:BEL was found to have a higher threshold for lasing. Both rods had slope efficiencies of 42%. The dependence of the output power on output mirror reflectivity was measured, with Nd:BEL showing a greater sensitivity to reflectivity than Nd:YAG. The optimum reflectivities were found to be .98 and .97 for Nd:BEL and Nd:YAG respectively. The maximum TEMOO cw power achieved for each rod at these reflectivities was 250 mW for Nd:BEL and 283 mW for Nd:YAG. We conclude that under the conditions used in this work, both BEL and YAG hosts perform comparably.

ISSN:0094-243X    

DOI:10.1063/1.37388

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We report the highest electrical to optical conversion efficiency (12.5%), and the highest cw output power (750 mW), from any solid state laser crystal end pumped by a single multiple stripe diode laser array. The optical slope efficiency, which refers to the 1.06 &mgr;m output power divided by the optical pump power incident on the end face of our laser crystal, was measured to be 64% in the best case and corresponds to nearly a 95% Nd quantum conversion rate, the highest yet reported.

ISSN:0094-243X    

DOI:10.1063/1.37353

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Over 250 mW of CW laser emission at 1084 nm is obtained from Nd:LiNbO3when the rod is end‐pumped along the crystalline’y’axis by 1 W from a Kr+laser at 752 nm. The laser can be tuned over 3 nm at the 1084 nm peak with a thin, uncoated etalon in the cavity. Thresholds of 30 mW of absorbed pump power were obtained with a weak output coupler, rising to 220 mW with a 35% transmitting output mirror. No pump‐induced photorefractive effects were observed.

ISSN:0094-243X    

DOI:10.1063/1.37361

出版商:AIP    

年代:1988

数据来源: AIP