A hydrogen-bonded organic nonlinear optical crystal for high-efficiency terahertz generation and detection

Abstract

Broadband THz pulses have been generated in 2-[3-(4- hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene]malononitrile (OH1) by optical rectification of sub-picosecond laser pulses. We show that OH1 crystals allow velocity-matched generation and detection of THz frequencies in the whole range between 0.3 and 2.5 THz for a pump laser wavelength range from 1200 to 1460 nm. OH1 crystals show a higher figure of merit for THz generation and detection in the optimized range compared to the benchmark inorganic semiconductor crystals ZnTe and GaAs and the organic ionic salt crystal 4-N,N-dimethylamino-4'-N'-methyl stilbazolium tosylate (DAST). The material shows a low THz absorption coefficient alpha3 in the range between 0.3 and 2.5 THz, reaching values lower than 0.2mm(-1) between 0.7 and 1.0 THz. This is similar as in ZnTe and GaAs, but much lower than in DAST in the respective optimum frequency range. A peak THz electric field of 100 kV/cm and a photon conversion efficiency of 11 percent have been achieved at a pump pulse energy of 45 microJ.

Generation of broadband THz pulses in organic crystal OH1 at room temperature and 10 K

“…The overall THz pulse spectra are in good agreement with the THz linear absorption spectra of the OH1 crystal shown in Fig. 4(a) and with previously reported spectra of THz pulses generated in this crystal [26]. Unfortunately, the Fourier spectrometer used for spectrally resolved THz transmission measurements of the OH1 crystal (Fig.…”

“…An increase in THz pulse power in the 2−2.2 THz spectral range observed upon cooling is determined by two effects: a decrease in THz absorption and better phase-matching at these frequencies due to a narrowing of the absorption band at 3 THz. In previous experiments at room temperature [26], a small increase in THz spectral power in this frequency range could be achieved by improved phase matching by tuning the pump laser wavelength from 1400 nm to 1250 nm.…”

Efficient metallic spintronic emitters of ultrabroadband terahertz radiation

“…For above-band-gap excitation, the response is dominated by a photocurrent 18,19,20,21,22,23,24 with a temporally step-like onset and, thus, generally smaller bandwidth than optical rectification 9 . Apart from rare exceptions 14 , however, most semiconductors used are polar 1,2,12,13,15,16,17,21,22 and strongly attenuate THz radiation around optical phonon resonances, thereby preventing emission in the so-called Reststrahlen band located between ~1 and 15 THz.The so far most promising sources covering the full THz window are photocurrents in transient gas plasmas 9,10,25,26,27,28,29 . The downside of this appealing approach is that the underlying ionization process usually requires amplified laser pulses with high threshold energies on the order of 0.1 mJ.…”

Strong-field single-cycle THz pulses generated in an organic crystal

“…13 Broadband THz pulses exceeding 10 THz were recorded for DAST pumped with an 800 nm Ti:sapphire laser, 14 and field strength up to 100 kV/ cm at a central frequency of 2 THz could be demonstrated for DAST pumped with a (near-) infrared source. 15 In this letter, we present high-power single-cycle THz pulses with electric fields beyond 1 MV/cm and with a corresponding magnetic transient of larger than 0.3 T. The generation is based on OR in the organic salt crystal (4 -N,Ndimethylamino-4 0 -N 0 -methyl stilbazolium tosylate) known as DAST which is driven by a powerful femtosecond infrared laser. The nonlinear conversion process gives rise to carrierenvelope phase (CEP) stabilized THz pulses at a center frequency of 2.1 THz with a bandwidth of 2 THz at full width half maximum (FWHM).…”