8-beam local oscillator array at 47 THz generated by a phase grating and a quantum cascade laser

Abstract

We present an 8-beam local oscillator (LO) for the astronomically significant [OI] line at 4.7 THz. The beams are generated using a quantum cascade laser (QCL) in combination with a Fourier phase grating. The grating is fully characterized using a third order distributed feedback (DFB) QCL with a single mode emission at 4.7 THz as the input. The measured diffraction efficiency of 74.3% is in an excellent agreement with the calculated result of 75.4% using a 3D simulation. We show that the power distribution among the diffracted beams is uniform enough for pumping an array receiver. To validate the grating bandwidth, we apply a far-infrared (FIR) gas laser emission at 5.3 THz as the input and find a very similar performance in terms of efficiency, power distribution, and spatial configuration of the diffracted beams. Both results represent the highest operating frequencies of THz phase gratings reported in the literature. By injecting one of the eight diffracted 4.7 THz beams into a superconducting hot electron bolometer (HEB) mixer, we find that the coupled power, taking the optical loss into account, is in consistency with the QCL power value.

3.9 THz spatial filter based on a back-to-back Si-lens system

“…One can use a lens and an iris aperture to achieve a quasi-Gaussian beam, as our group did in [21], but the efficiency is very low (∼10%). Two off-axis parabolic mirrors combined with a pinhole can also be used as a beam filter with an efficiency of 22% [22], but the system is bulky and the alignment of the whole system is challenging. In our approach, a lens with an elliptical front surface is chosen because it couples well to a Gaussian-beam at its minimum waist [34] and its on-axis beam has no aberrations if the eccentricity is equal to the reciprocal of the refractive index of the lens material [35].…”

“…For heterodyne mixer arrays, phase gratings are used as the multiplexer, which diffracts a single QCL beam into multiple beams as an array LO [20] and recently reported up to 81 beams [21]. To avoid overlap between the individual diffracted beams, a Gaussian input beam to the grating is required [22,23].…”

Температурная Зависимость Порогового Тока И Выходной Мощности Квантово-Каскадного Лазера С Частотой Генерации 3.3 ТГц

“…В настоящее время квантово-каскадные лазеры (ККЛ) являются компактными твердотельными когерентными источниками терагерцового излучения в диапазоне от 1.2 до 5.0 ТГц. Большая выходная мощность [1], возможность перестройки частоты [2] и получения узких линий генерации [3] делает ККЛ наиболее перспективным ТГц-источником для реализации терагерцовой спектроскопии нового поколения [4], систем терагерцовой визуализации в реальном времени [5], а также для использования в качестве локального осциллятора для гетеродинного детектирования [6].…”

81 supra-THz beams generated by a Fourier grating and a quantum cascade laser

“…A phase grating has played a crucial role in optics-related science and applications, including orbital angular momentum beams for optical communications, chromatic broadband nulling, UV and terahertz beam multiplexing, and complex beam shaping [15][16][17][18][19]. A phase grating is a periodic structure converting a single coherent radiation beam into multi-beams in different directions by manipulating the phase of the input beam.…”

“…A 7 pixel grating operated at 1.1 THz with diffraction efficiency ~80% has also been realized in [26]. Recently, Mirzaei et al in [27] have pushed the frequency further to 1.4 THz, and even to the 4.7 THz with a 2 × 4 Fourier grating with a diffraction efficiency of 74% in [18]. A 4.7 THz grating of 2 × 4 will be used as an LO multiplexer for mapping [OI] line emission in Galactic/extragalactic Ultra long duration balloon Spectroscopic Stratospheric THz Observatory (GUSTO), which will be launched in 2021 [28].…”