637  μ W emitted terahertz power from photoconductive antennas based on rhodium doped InGaAs

Abstract

We investigate photoconductive terahertz (THz) emitters compatible with 1550 nm excitation for THz time-domain spectroscopy (TDS). The emitters are based on rhodium (Rh) doped InGaAs grown by molecular beam epitaxy. InGaAs:Rh exhibits a unique combination of ultrashort trapping time, high electron mobility, and high resistivity. THz emitters made of InGaAs:Rh feature an emitted THz power of 637 μW at 28 mW optical power and 60 kV/cm electrical bias field. In particular for a fiber coupled photoconductive emitter, this is an outstanding result. When these emitters are combined with InGaAs:Rh based receivers in a THz TDS system, 6.5 THz bandwidth and a record peak dynamic range of 111 dB can be achieved for a measurement time of 120 s.

Roadmap of Terahertz Imaging 2021

“…A similar tendency can be seen in the evolution of femtosecond fiber lasers-based optoelectronics THz systems: Their emitted power has increased from several microwats [35] in 2010 to 637 µW in 2020 [37].…”

“…These studies also indicated sensitivity of the proper materials design for effective THz emission in various types of TDS systems. Another recently study announced promising approach relies on MBE grown rhodium (Rh) doped InGaAs which exhibits a combination of ultrashort trapping time, high electron mobility, and high resistivity [37]. Because of these features, fiber coupled photoconductive THz emitters exhibit impressive characteristics: They delivered THz power amounts to 637 µW, the bandwidth extends up to 6.5 THz, and a record peak dynamic range reaches a value of 111 dB.…”

“…Optoelectronic THz systems (denoted as red solid lines) are attributed for the emitters section only. The left red solid line depicts facilities of optoelectronic InGaAsBi-based systems[36], the right one-the system relying on InGaAs:Rh compound[37]. Resonant tunneling diodes data are taken from publications by M. Asada[119,121], M. Feiginov[117] and H. Yokoyama[441] groups.…”

Frequency Selective Optoelectronic Downconversion of a Terahertz Pulse Using ErAs:In(Al)GaAs Photoconductors

“…Both factors can be significantly improved. Similar EO generated frequency combs with a frequency coverage of around 1 THz have already been demonstrated [32], while pulsed PCAs emitting terahertz powers almost one order of magnitude higher than the used here have also been shown [16]. This would allow a thorough characterization of the phase noise evolution of the several thousands of modes composing the terahertz pulses generated by passively locked MLLs.…”

“…We employ two lines of an electro-optically (EO) generated frequency comb to produce a continuous wave (CW) terahertz signal that acts as a photonic local oscillator for the optoelectronic downconversion of the individual frequency components of a terahertz pulse. We therefore call this scheme Frequency Selective Optoeletronic Downconversion (FreSOD), feasible thanks to the recent developments in telecom-wavelength compatible PCAs [11]- [15]: when acting as emitters in pulsed operation, telecom-wavelength PCAs are now capable of delivering powers in excess of 0.5 mW [16], while CW receivers have shown noise equivalent powers (NEPs) as low as 1.8 fW/Hz [17]. For this particular implementation, we have used stateof-the-art ErAs:In(Al)GaAs PCAs, which have shown an excellent performance in both CW and pulsed operation.…”