We have developed a truly unique experimental facility, called the Rice Advanced Magnet with Broadband Optics (RAMBO). This facility houses an ultracompact pulsed magnet capable of producing a peak field of 30 Tesla, combined with an arsenal of state-of-the-art instruments for modern materials research. A unique feature of this system is the marriage of a strong magnetic field and ultrashort laser pulses from nearly “DC to daylight.” This unconventional coupling of two extreme conditions will likely lead to new scientific knowledge, advancing the frontier of materials research.
Illustration by Tanyia Johnson/Rice University
RAMBO represents a new type of experimental facility, one that mates low-cost, high-field pulsed magnets that feature excellent optical access to the sample with state-of-the-art ultrafast optical probing at a wide range of wavelengths. We have built a highly flexible and usable optical system around the RAMBO Magnet, providing a variety of sources and detectors, covering wavelengths in the terahertz (~200 µm), the mid-infrared (MIR) (~3-16 µm), and the near-infrared (NIR)/visible regime (~0.8 µm and harmonics), all with ~100 fs time resolution.
Figure 1: Top: Exponentially damped half sine wave profile. Bottom: Exponentially damped single sine wave profile. The Top uses a ‘crowbar’ diode antiparallel to the coil, and the Bottom uses a diode antiparallel to the thyristors.
Figure 2: 5.6 mF capacitor bank on casters making the system portable.
Figure 3: 1.25″ diameter mini-coil, similar to the 1.7″ diameter coil used in the system.
The RAMBO Magnet is a pulsed mini-coil magnet (Fig. 3), with a bore of 12 mm × 58 mm, allowing for optical access in a cone half-angle of 12.4°. It produces peak fields of 30 T with a pulse length of ~10 ms (Fig. 1). It is liquid-nitrogen cooled and can generate 30 T pulses at the rate of ~1 per 10 minutes, or 5-7 T pulses every 1 minute. The Magnet is fed by a capacitor-bank pulse generator (Fig. 2). In continuous use, the Magnet draws less than 1 kW average electrical power from a standard outlet.
Figure 4: The RAMBO Magneto-optical cryostat system attached to table-top.
The sample is held in the Magnet’s bore by a hollow sapphire cold finger (Fig. 4) attached to a separate cryostat. Front-side access to the sample is unimpeded within the cone angle of 23.4°, allowing for a high numerical aperture (NA = 0.20). The hollow sapphire cold finger allows backside access to the sample for well-collimated or weakly-focused optical beams. Thus, optics experiments can be performed in transmission or reflection. It will be possible to insert and/or collect essentially any combination of wavelengths via free space with good focusing ability, good spatial resolution, and with low dispersion. This is a quantum leap above magnets with limited optical access, which are severely constrained in all these aspects of performance.
Main Research Equipment:
- Amplified Ti:Sapphire Laser (Clark-MXR, Inc. CPA-2001)
- 2 TOPAS OPAs (Light Converstion Ltd.)
- Silicon Charged Coupled Device (CCD)
- G. T. Noe, H. Nojiri, J. Lee, G. L. Woods, J. Léotin, and J. Kono, “A Table-Top, Repetitive Pulsed Magnet for Nonlinear and Ultrafast Spectroscopy in High Magnetic Fields Up to 30 T,” Review of Scientific Instruments 84, 123906 (2013). (abstract, full text, Rice News)
- G. T. Noe, Q. Zhang, J. Lee, E. Kato, G. L. Woods, H. Nojiri, and J. Kono, “Rapid Scanning Terahertz Time-Domain Magnetospectroscopy with a Table-Top Repetitive Pulsed Magnet,” Applied Optics 53, 5850 (2014). (abstract, full text, arXiv)