Facilities, Equipment and Other Resources:
The Physics laser lab is located at the FORT Interdisciplinary Research Center, which is home for several research centers.
MAJOR EQUIPMENT.
Two 20 Hz ND: YAG Laser (Continuum Surlite II) with a double and triple output pumping two Continuum ND 6000 dye lasers, a UVX: frequency doubling and tracking system. These lasers are only 5 years old and still in very good shape. One of the Surlite lasers is only 4 years old.
A Continuum Leopard pico second laser with second, third and fourth harmonic generating crystals. (New). This laser delivers < 20 ps pulses in 266-nm, 355–nm and 532-nm. The energy at 266 nm is about 4mJ.
Reflectron Time of Flight mass Spectrometer: with pulsed source and effusive source
This equipment is very versatile and designed to accommodate several other sources including electron gun, MALDI source, and a laser ablation source insert. There are also windows to allow lasers at the reflectron region.
Figure below shows schematics of the RTOF manufactured by Atom Sciences Inc. The RTOF incorporates a two-stage acceleration field; the initial acceleration region is approximately 1/10 that of the final acceleration. With this configuration, the energy difference caused by the spatial distribution of ions is much smaller than in one-stage acceleration and greater mass resolution is achieved. A reflectron time-of-flight mass spectrometer, such as the RTOF-300 has an additional means of time focusing the ions of same mass onto the detector at the same time. The RTOF uses an ion mirror to bend the ions through about 174° before they are allowed to strike the detector. Ions with higher energy (due to initial energy distribution or to initial spatial distribution) penetrate farther into the mirror before being turned around, thus providing a longer path for the faster, higher energy ions.
The Knudsen region has the following features:
· The Knudsen cell (K-Cell) is a water-cooled, single-filament effusion cell (Model EPI-10-M-L from Veeco) mounted on a bellows translation stage that provides up to 12” vertical motion.
· A programmable motor (model SM2337D-T from Animatics) raises and lowers the Knudsen cell according to the position of a switch on the status/control box. The motor has programming stored in its memory.
· Sample loading chamber – In the down position, the top of the K-cell is just below the center of the sample-loading chamber. When the K-cell is down and cold and the gate valve is closed, the loading chamber can be vented. The pressure in the loading chamber is monitored via a Pirani gauge, P3, with readout on the computer.
The source chamber is a custom 8” tube with 10” conflat flanges at each end and multiple ports. Several components are attached to this chamber:
· A Pfeiffer model TMU 521-turbomolecular pump, TMP2, is mounted horizontally on the chamber and provides the main pumping for this region. The TMP2 is backed by a Pfeiffer model DUO 5 mechanical pump, and the roughing pressure is monitored by a Pirani gauge.
· The pressure in the source chamber is monitored by a Granville Phillips model 354 dual filament ion gauge, which is mounted on a 2-3/4” port. The pressure can be read at the gauge or on the computer screen.
Figure 1. The RTOF-300and the lab available for this work.
· A cooling baffle assembly is mounted on the 10” end flange. This baffle extends between the RTOF ion source and the mouth of the K-cell. A small hole in the baffle serves to aperture the K-cell effusive beam.
· A mechanical shutter is also mounted on the 10” end flange. This shutter can be positioned to block the K-cell effusive beam, preventing it from passing through the hole in the cooling baffle. This protects the ion source from unnecessary deposits.
· A pulsed valve (R.M. Jordan) is mounted horizontally on a 6” flange. This valve is triggered by the computer.
· The Knudsen chamber is attached to the source chamber through a port on the bottom of the Source Chamber. A connecting gate valve can be closed to isolate the two chambers.
· Ion Source – The ion source is mounted at the end of the flight tube. The ion source is comprised of a repeller plate, an acceleration region, a short field-free region bounded on both sides by high-transparency mesh held at ground potential, a second acceleration region, and a third mesh that serves as the entrance to the flight tube. Ions are formed in the region between the repeller plate and the first field-free region. After the ions pass through the initial field-free region, they accelerate over a short distance to the flight tube entrance.
The RTOF Chamber is composed of several components:
· The flight tube, which is maintained at a constant potential, typically –2000 V to –5000V (for positive ions). Once inside the flight tube, the ions are essentially in an extended field-free region at flight tube potential, VFT, except for fields generated by the x and y deflection plates and the focusing lens (Einzel lens). The deflection plates are two pair of electrodes (one pair for x deflection, and one pair for y deflection) biased at VFT. The focusing lens is a single cylindrical electrode.
· A gridless ion mirror, is composed of a stack of conducting rings electrically connected by high impedance resistors. The ring nearest the flight tube is physically and electrically connected to the flight tube so that this ring is at VFT potential.
There are two detectors:
o A dual microchannelplate detector (called the linear detector) behind the ion mirror. This detector is typically used only for initial alignment.
o A second dual microchannelplate detector (called the reflectron detector) at the end of the second leg of the flight tube.
The mass resolution of the system is 500 m/Dm. The system is fully computer controlled and uses Labview.
The electron impact ionizer has been added recently. This is a simple filament device with a pulsed anode and lens assembly. It produces pulsed, focused electrons at the ionization region. The bias voltage, filament current, anode delay, anode width, and lens voltage are user-controlled by a rack-mounted power supply
OTHER EQUIPMENTS
Other Accessories include a 35 cm McPherson Monochromator, a SPEX Spectrometer, a Tektronix digital oscilloscope, Le Croy 4 channel,3GHz with 20 GS/s sampling rate oscilloscope, Box Car averager and gated integrator system (Stanford System), Power Supply (Stanford), Temperature controllers (Omega Engineering), PMT, PMT cooled housing, Lab-view controlled data acquisition, a chart recorder, pumps, capacitance manometer 100 torr range, flow meters (very sensitive), several heat pipe ovens, high power mirrors, quartz lenses and several other optical components, lens mirror holders, translation stages, optics mounts, optical tables (4’x 6’, 4’ x 12’, 4’ x 8’ sizes) vacuum parts and several PC’s.
For computational needs:
Eight paralleled dual- processor Apple Macintosh G5’s (“Big-Mac”) is running in the Department of Physics at NCA&T
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