Magneto-optics

Infrared

The DC Field Facility has installed a Bruker Model IFS 113v Fourier transform infrared spectrometer. The specifications of the spectrometer and its accessories are:

• Range: 10,000 to 10 cm^-1
• Resolution: Better than 0.03 cm^-1
• Sources: SiC glowbar, W lamp and Hg lamp
• Beamsplitters: Ge on KBr, 4 mylar films and CaF2
• Detectors: DTGS with KBr and polyethylene windows, Si bolometer with dewar and preamp, InSb detector with dewar and preamp
• Automation: 3 sources, 4 apertures, 4 filters, 6 beam splitters and 4 detectors
• Sample holders: A cryostat with light pipe and sample changer for transmission measurements and a cryostat with light pipes for reflection measurements may be used in the superconducting and resistive magnets in the Tallahassee facility. Sample temperatures can be controlled between 1.6 K and 100 K. The sample can be angled between 60 and 90 degrees to the field direction. We have recently found that excellent measurements can be made at frequencies up to 3000 cm^-1 with the light pipe system.

An infrared laser is available for use in transmission and reflection measurements and for optical pumping. The laser is shared with the Electron Magnetic Resonance group for electron spin resonance in high magnetic fields.

There has been vigorous discussion with present and prospective users of facilities for infrared research in high fields. All agreed that the equipment must be user friendly. A big part of that is having someone locally to use, maintain and improve the equipment and to help users. The Magnet Lab therefore supports research in semiconductor physics using IR spectroscopy as part of its in-house science program.

Ultra-Violet, Visible and Near Infrared

All of the sources and spectrometers at the Mag Lab now are coupled to the experiment in the magnet via optical fibers. This allows the lasers and some of the spectrometers to remain in one place, even though experiments are done in pulsed magnets, resistive magnets or superconducting magnets located at some distance. Experiments can be done at wide ranges of temperature and pressure. Similar capabilities exist in Los Alamos and Tallahassee.

Complete laser systems provide wavelengths from the near ultraviolet to the near infrared at both locations. Each includes a Coherent MIRA 900 dual mode locked Ti:Sapphire laser capable of operating in the pulsed (femtosecond or picosecond) or continuous wave modes, a 10 W argon laser to pump the Ti:Sapphire, and a 7 W, UV capable argon laser. The lasers have the following wavelengths:

• 351.1 nm (300 mW)
• 363.8 nm (300 mW)
• 488.0 nm (2.4 W)
• 514.5 nm (3.3 W)
• a tunable band for the Ti:Sapphire (>=100 mW continuous wave output) of 700 - 1050 nm

The time scales of the Ti:S laser in mode locked operation are 130 fs and 2 ps, and the wavelength range is 720 nm to 1000 nm.

The following equipment is available for pulsed fields and in the 20 T superconducting magnet in Los Alamos:

• 0.25m, f/4 Jarrel-Ash monochromator with a thermoelectrically cooled GaAs photomultiplier and a liquid nitrogen cooled Ge photo-detector for operation in the visible and near IR (300-1600 nm)¹
• 0.6m, f/10 Spex 'Triple-Mate' spectrometer [1] with a Photometrics Model 9000 CCD array detector [2] for the 300-1050 nm region
• 0.28m, f/4 Acton Instruments monochromator with a Princeton Instruments CCD array detector [3] for operation in the 300-1050 nm region
• Sample holders for both pulsed and superconducting magnets at temperatures from 1.6 K to 300 K. Samples may be oriented either parallel or perpendicular to the applied field
• Diamond anvil cells for optical studies at pressures up to 17 GPa
• Techniques used have included photoluminescence, transmission and reflection spectroscopy

Users of the resistive and superconducting magnets in Tallahassee have available a MacPherson 0.75 m single grating monochrometer/spectrometer. The accessories on hand provide 0.01 nm resolution and cover wavelengths from 300 to 1050 nm (7 gratings). It is highly automated and features a UV coated 1024 X 256 CCD array detector for rapid spectroscopy in high fields (over 125 spectra in a single 3.5 hour shift).

The following other equipment is available for use in the resistive and superconducting magnets in Tallahassee:

• Holographic notch filters at 488.0 nm and 514.5 nm
• Long Pass and short pass filters from 250 nm to 1000 nm
• Sample holders are available for all of the superconducting and resistive magnets
• Sample temperature control from 1.6 K to 300 K while situated in a vacuum can in the helium dewar
• The sample holder for the 50 mm bore resistive magnets has sample changing capability for up to seven 5 mm diameter samples
• Techniques used have included photoluminescence and reflection
• HeCd laser with 40 mw at 325 nm
• Arlon laser with 100 mw at 275 nm spectroscopy

[1] Equipment supplied by Dr. Clive Perry, Northeastern University.
[2] Equipment supplied by Dr. Bernhard Laurich, LANL.
[3] Operational February 1995.