Laser tuning

Figure 9. Action spectra acquired in the F Cl B—X, 3-0 spectral region and with the probe laser tuned to the F Cl E—B, 9-1 transition. Both spectra were recorded using the same source conditions, but with the lasers intersecting the expansion at Z = 8.8, (a), and Z = 19.1, (b). Monomer rotational temperatures of 2.34(3) K and 1.09(10) K were measured at the two distances [62].

Since our main objective was to remove all the chlorine and hydrogen atoms from the polymer chain, C-PVC films were further exposed to the UV radiation of the medium pressure mercury-lamp. This led to a dark brown material w.hich was found to be unable to carry an electrical current, even after extended irradiation time. Therefore we turned to a powerful laser source, a 15 W argon ion laser tuned to its continuous emission at 488.1 nm. At that wavelength, the degraded polymer film absorbs about 30 % of the incident laser photons. The sample was placed on a X-Y stage and exposed to the laser beam at scanning rates in the range of 1 to 50 cm s, in the presence of air. 

Ytf -ZBLANP sample when it is illuminated at room temperature by a laser tuned at 1000 nm. 

Details of the laser system and the operating conditions employed to control the lasers have been described previously [6]. The system includes two independently operated distributed feedback (DFB) InGaAsP diode lasers tuned over the desired transitions near 1.34 p,m and 1.39 p,m i/ + I s bands)... 

In the MALDI technique a pulsed laser beam strikes a solid sample and heats, vaporizes, and ionizes compounds with little decomposition.201-209 Proteins or other biopolymers are mixed with a "matrix" Fiat absorbs the heat of Fie laser beam. The protein sample together with Fie matrix is dried. Most proteins form crystals and Fie laser beam is directed toward individual protein crystals or aggregates. Various materials are used for the matrix. Compounds as simple as glycerol, succinic acid, or urea can be used with an infrared laser. For proteins an ultraviolet nitrogen laser tuned to 337 nm is usually employed with an ultraviolet light-absorbing matrix such as hydroxy-benzoic acid, 2,5-dihydroxybenzoic acid, a-hydroxy-... 

The steady state OH concentration in the atmosphere has been measured by the fluorescence technique using a dye laser tuned near 2820 A [Wang and Davis (1006), Davis ct al. (267)] or a microwave excited OH resonance lamp [Anderson (42)]. 

Analyze with a flow cytometer with an argon-ion laser tuned to 488 nm. Record the light emitted into the red fluorescence photomultiplier tube (PMT) using a 620-nm long pass filter in front of the PMT. 

While ionization by linearly polarized fields has been well studied, there is only one report of ionization by a circularly polarized field, the ionization of Na by an 8.5 GHz field.36 In the experiment Na atoms in an atomic beam pass through a Fabry-Perot microwave cavity, where they are excited to a Rydberg state using two pulsed tunable dye lasers tuned to the 3s — 3p and 3p —> Rydberg transitions at 5890 A and —4140 A respectively. The atoms are excited to the Rydberg states in the presence of the circularly polarized microwave field which is turned off 1 fis after the laser pulses. Immediately afterwards a pulsed field is applied to the atoms to drive any ions produced by microwave ionization to a microchannel plate detector. To measure the ionization threshold field the ion current is measured as the microwave power is varied. 

Zuckermann et al. [119] studied IR multiphoton dissociation (IRMPD) of RDX and HMX in a supersonic jet. A C02 laser was used for dissociation, with a pulsed frequency-doubled dye laser tuned to 280nm to excite the A 22(v = 1) X2 (v = 0) transition... 

Simultaneously with the ionization signals we monitored fluorescence signals. Gated integrators processed both these signals. We observed ionization signals with the laser tuned to... 

Figure 1. Ionization charge as a function of the distance between the probes. The probe in contact with the laser beam ("beamprobe") is kept in a fixed position. Upper curve, beamprobe negative lower curve, polarity of probes reversed. Laser tuned to 3Sl/lt - 3P /t transition. Power density of the laser pulse is 7 X 10 W/ cm2 diameter of laser beam is 3 mm.

The experimental arrangement is basically similar to that of Hansch et al. (4). A Spectra Physics Ar+ laser operating at 514.5 nm pumps a Rhodamine 6G dye laser tuned with a birefrin-gent filter. The linewidth is 25 to 30 GHz, and the wavelength is tuned between 585.0 nm and 585.2 nm. The output mirror has a 1 meter radius of curvature and a reflectivity of 98% at 585.0 nm. The dye laser cavity is 74 cm long, and the laser is always run TEMoo (this sometimes necessitates the use of an intracavity aperture). 

A quantitative study of the RISC quantum yield was carried out with 55 [37]. This study involved UV irradiation of 55 in benzene or cyclohexane solution to produce the 7, state and subsequent photolysis by a second laser tuned to the T-T absorption band. The second pulse was accompanied by depletion (bleaching) of the T-T absorption and 5, — S0 fluorescence [the fluorescence was detected and quantified by an optical multichannel analyzer (OMA)]. The quantum yield of RISC, d>RISC, was calculated using Aberchrome 540, a reversible fulgide, as a two-laser actinometer. The values for benzene solvents, respectively. This compares with 0.19 found for 55 in ethanol solvent [36]. 

Since the Y-photon ionization rate is R = aN F, where ionization cross-section and Fthe photon fluence, both the electron and ion signals can be increased by tight focussing of the laser. Because the ion yield should increase as the Y-th power of the intensity, focussed lasers tuned to an intermediate resonance will ionize virtually every atom in the focal volume. For a typical dye laser with 0.5-mrad divergence, the spot size for a 5-cm focal length lens is 25 /mi which, for an assumed energy of ca 10 mJ per 10 ns pulse (i.e. 1 MW of power), yields a flux p of ca 1011 W cm-2. This power density corresponds, for 500-nm photons, to a fluence of ca 5 x 1022 photon cm-1. Since the peak electric field, E V cm 1, is related to p by... 

Laser spectroscopy of pHe+ was established according to the proposal of Morita et al. [10], which is to apply a pulsed laser tuned to a transition between a... 

Fig 5 Bandwidth of an FM dye laser tuned by a three plate birefringent filter as a function of the detuning between the passive node spacing and the driving frequency applied to the phase modulator. 

Polyimide KAPTON films were irradiated using a Lambda-Physik EMG200 Excimer laser tuned to 193 nm radiation (ArF). The samples were treated in air, at different fluences all received 10 shots at the repetition rate of 10 Hz. Surface analysis of the different samples was performed using an ESCA-201 system (SSL) with an x-ray microspot facility (150 nm). 

Figure 8. a Nag laser tuning curve (----). Pump power, 1.5 W length of vapor... 

Figure 6.1-29 Ionization detected stimulated Raman (IDSRS) spectra of benzene in the region of overlap between the "0-branch transitions of and the S-branch transitions of V2 + v ,. (a) UV laser tuned to 36 467 cm (b) UV laser tuned to 36 496 cm (Esherick et al 1985).

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