Widely Tunable, Semiconductor THz Laser

IB-1161

E.O. Lawrence Berkeley National Laboratory APPLICATION OF TECHNOLOGY: Terahertz (THz)imaging and THz vision IR and far-IR optical instrumentation Trace gas and atmospheric monitoring Supramolecular chemistry Military applications such as radar modeling and scale-model radar THz imaging ADVANTAGES: Broad tuning range 1 - 4 THz, high laser power (a few µW to several Watts), and high duty cycles up to 5% Electrically controlled solid state lasers provide safe, maintenance-free operation, with no need for toxic gases Can be operated in commercially available closed-cycle refrigerators All solid state

ABSTRACT:

Eugene Haller and Erik Brundermann have invented a new type of semiconductor THz and far-IR laser using lightly doped p-type germanium single crystals grown at Berkeley Lab. By changing an electric and/or magnetic field the laser can generate laser pulses or radiation tens of microseconds long with frequencies in the THz frequency range (1-4 THz, corresponding to 75-300 µm, 35-130 cm ^-1 or 4-16 meV).

The laser is operated in closed-cycle refrigerators but low temperature cryostats can be used as well. The laser is safe, maintenance-free, and electrically controlled. In contrast, commercially available THz radiation generators are large (100 ft²), sensitive gas lasers that have emission spectra covering only a limited range of frequencies. The handling of these lasers is complex and involves using hazardous gases CH2F2 or HCOOH to operate them and undesirable CO2 lasers to pump them.

The magnetic field is applied by superconducting coils or small and inexpensive permanent magnets with a volume of about 1cm³. The maximum emission power depends on the crystal volume and can reach from a few µW to several Watts with duty cycles of up to 5%. Current research is heading for continuous wave emission (100% duty cycle).

Berkeley’s versatile, widely tunable laser source is relevant to areas that can make use of low and high resolution spectroscopy with a finesse of up to 10⁷ in the THz range such as: THz imaging and THz vision, environmental monitoring of trace gases (NO_x, CO, etc.), monitoring of the atmosphere, IR and far IR optical instrumentation, and measuring van der Waals bonding energies in biomolecules or organic semiconductors.

The high intensity THz pulses of a 0.4 cm³ laser can penetrate water layers of approximately 1 mm thickness which makes the study of biomolecules or living cells in their natural environment feasible. This is a major advantage compared to Fourier Trnasform spectrometers and other low intensity sources typically used in this frequency region. Military applications might be found in radar modeling and scale-model radar THz imaging.

Berkeley Lab seeks partner(s) in the development of a computer controlled laser system based on this new germanium laser. Some assistance developing prototypes could be provided.

STATUS: U. S. Patent #6,011,810. Available for licensing

FOR ADDITIONAL INFORMATION PLEASE SEE:

http://www.mse.berkeley.edu/groups/haller/brundermann/technology_transfer.html

PUBLICATIONS:

• E. Bründermann, D.R. Chamberlin, and E.E. Haller, “High duty cycle and continuous terahertz emission from germanium,” Appl. Phys. Lett. 76, 2991-2993 (2000).
  
• D.R. Chamberlin, E. Bründermann, and E.E. Haller, “Planar contact geometry for far-infrared germanium lasers,” Appl. Phys. Lett. 74, 3761-3763 (1999).
  
• E. Bründermann, D.R. Chamberlin, and E.E. Haller, “Novel design concepts of widely tunable germanium terahertz lasers,” Infrared Phys. Technol. 40(3), 141-151 (1999).

REFERENCE NUMBER: IB-1161

U.S. DEPARTMENT OF ENERGY • OFFICE OF SCIENCE • UNIVERSITY OF CALIFORNIA

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