Danielle Russell Chamberlin

High duty cycle and continuous terahertz emission from germanium

We measured laser emission from Be-doped Ge crystals with intercontact distances as small as 0.5 mm. An improved heat sink allowed a twofold increase of the laser duty cycle to 5%. We also report the measurements of THz emission from small Be-doped Ge crystals under continuous excitation with volumes as small as 0.5 mm3.

Thermal effects in widely tunable germanium terahertz lasers

We report laser emission from Be-doped Ge lasers at high repetition rates of up to 45 kHz which is one order of magnitude higher than previously reported. Laser radiation was detected from Ge:Be crystals with volumes as small as 0.5u2009mm3 and with intercontact distances down to 1 mm. We present a thermal analysis and derive the design parameters for continuous wave Ge lasers.

Novel design concepts of widely tunable germanium terahertz lasers

Abstract We explore the full parameter space for laser operation and compile guidelines for building improved Ge lasers, especially for continuous wave applications. We present laser emission from p-type Ge lasers with small volumes at high repetition rates and with inter-contact distances as low as 750 μm. The emission is analyzed as a function of the current–voltage characteristic. The Poisson equation is solved to determine the electric field distribution and two new laser designs are presented.

Planar contact geometry for far-infrared germanium lasers

We demonstrate operation of p-Ge far-infrared lasers with a planar contact geometry. The smallest laser crystal with this geometry has a maximum pulse length of 22 μs, which is 10% longer than the pulse length of comparably doped lasers with the traditional contact geometry. Calculations of the electric field distribution show that the fraction of active crystal volume for this new geometry is ∼four times larger than that of traditional geometries. Experiments and calculations reveal that in the planar design, the minimum applied voltage necessary for lasing decreases when the crystal geometry approaches a flat planar structure. This is due to a significant increase of the total electric field caused by the Hall effect.

Mode-locked operation of the copper-doped germanium terahertz laser

We have fabricated a copper-doped germanium laser using copper diffusion into commercially available pure germanium. The spectrum and the emission pulses of this laser were investigated. Active mode locking was achieved with pulse lengths of 160 ps at full width half maximum. The current Ge:Cu laser does not yet reach the performance of an earlier studied Ge:Ga laser although mode-locked Ge:Cu lasers promise much shorter pulse lengths and wavelength tunable pulses due to the absence of acceptor related absorption. Possibilities to optimize the laser will be discussed.

Widely tunable high-duty-cycle semiconductor terahertz lasers

Germanium terahertz (THz) lasers based on a heavy hole-light hole population inversion within the valence bands show strong promise for widespread applications due to their unparalleled frequency tuning range and high output power up to several Watts. Germanium lasers have attractive laser properties: tunability from 1 to 4 THz, high finesse of 106 with line widths below 1 MHz and linear polarization. Laser operation is possible with small mm- sized permanent magnets and closed-cycle refrigeration. Since 1995 we have increased the duty cycle (laser on-time) of such lasers from 10-5 up to 2.5 X 10-2 (2.5%). We report on our current research efforts aimed at achieving continuous wave emission. These efforts include a reduction of the active laser crystal volume from typical values of 30 - 60 mm3 to and perhaps below 1 mm3 and materials and electric field homogeneity improvements to enhance the conversion efficiency. A planar contact geometry is suggested to allow improved heat sinking. Our planned applications include but are not limited to airborne and satellite based research for the study of molecules in the upper atmosphere or in star-forming regions of the universe.