Fiber-dispersive Raman spectrometer with single-photon sensitivity.

The two major challenges in Raman spectroscopy are the low intensity of spontaneous Raman scattering and often accompanying luminescence. We overcome these two issues with a novel fiber-dispersive Raman spectrometer utilizing pulsed excitation and a superconducting nanowire single-photon detector (SNSPD). By exploiting chromatic dispersion in the fiber material, we stretched propagation times of Raman photons and performed correlated measurements in the time domain, where the two emission processes, Raman scattering and luminescence, can be effectively separated. The spectrometer greatly benefits from SNSPD metrics, i.e. broad spectral sensitivity (from UV to near-IR wavelength range) on a single-photon level and high timing resolution (small timing jitter), which outperform those of competing avalanche single-photon detectors. The spectral resolution achievable with a fiber-dispersive spectrometer for the optimized components is estimated to be as good as 3 - 10 cm-1 over the Stokes shifted range up to 4400 cm-1 with an excitation wavelength of 785 nm and below 5 cm-1 covering the same range with an excitation wavelength of 532 nm.

Si:P as a laboratory analogue for hydrogen on high magnetic field white dwarf stars.

Laboratory spectroscopy of atomic hydrogen in a magnetic flux density of 10(5) T (1 gigagauss), the maximum observed on high-field magnetic white dwarfs, is impossible because practically available fields are about a thousand times less. In this regime, the cyclotron and binding energies become equal. Here we demonstrate Lyman series spectra for phosphorus impurities in silicon up to the equivalent field, which is scaled to 32.8 T by the effective mass and dielectric constant. The spectra reproduce the high-field theory for free hydrogen, with quadratic Zeeman splitting and strong mixing of spherical harmonics. They show the way for experiments on He and H(2) analogues, and for investigation of He(2), a bound molecule predicted under extreme field conditions.

A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler.

We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. The whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments.

Stimulated terahertz stokes emission of silicon crystals doped with antimony donors.

Stimulated Stokes emission has been observed from silicon crystals doped by antimony donors when optically excited by radiation from a tunable infrared free electron laser. The photon energy of the emission is equal to the pump photon energy reduced by the energy of the intervalley transverse acoustic (TA) g phonon in silicon (approximately 2.92 THz). The emission frequency covers the range of 4.6-5.8 THz. The laser process occurs due to a resonant coupling of the 1s(E) and 1s(A1) donor states (separation approximately 2.97 THz) via the g-TA phonon, which conserves momentum and energy within a single impurity center.