Spectroscopy of optically pumped ammonia and deuterium oxide near 1 THz
Molecular gases like ammonia (NH<inf>3</inf>) and deuterium oxide (D<inf>2</inf>O) can be used as active media for optically pumped terahertz lasers (OPTL). In this paper we present spectroscopic measurement of chosen NH<inf>3</inf> and D<inf>2</inf>O lasing lines near 1 THz. Rotational-vibrational transitions are pumped by mid infrared quantum cascade laser (MIR QCL) which offers more precise tunability in MIR spectral range than standard optical pumping methods (CO<inf>2</inf>, N<inf>2</inf>O lasers). This allows to access new lasing lines. Frequency domain measurements of NH<inf>3</inf> and D<inf>2</inf>O under different pressure, pumping frequency and pumping power are performed. The results show high gain obtained for NH<inf>3</inf> (3,3) line at 1.073 THz and very low gain for D<inf>2</inf>O (4,3,2) line at 533 GHz due to the low population.
Solid-state terahertz laser materials based on molecular crystals
The progress in terahertz (THz) technology in the last years created a demand for new sources of terahertz radiation, which are required for utilization of its full potential in everyday applications. This thesis deals with subject of terahertz sources specifically development of novel terahertz lasers which would provide more efficiency and better tunability in a more compact package. To carry out this objective we chose two approaches. The first is the optimization of existing terahertz optically pumped molecular gas laser design. This type of lasers typically utilizes a mid-infrared CO2 discharge laser as optical pump to excite roto-vibrational states in gases. A CO2 optical pump has multiple drawbacks especially its size and a limited number of lines that can be optically pumped. Both drawbacks can be solved by the replacement of the CO2 laser by a mid-infrared quantum cascade laser, which is small, more efficient and continuously tunable, which allows almost perfect resonant pumping of a terahertz active molecular gas. With this in mind, we made a series of experiments evaluating lasing properties of molecular gases, mostly NH3, during optical pumping by a quantum cascade laser. New lasing lines were testes for terahertz gain with success.The second approach is the development of a completely new type of terahertz lasers based on optically pumped solid state media. The idea is to optically pump vibrational modes in molecular crystals and to obtain a change of population on low frequency phonons. Molecular crystal materials were selected as a potential lasing material due to their vibrational modes in mid-infrared and terahertz spectral range. Fourier transform infrared spectroscopy and terahertz time domain spectroscopy were applied to analyze vibrational spectrum of the chosen molecular crystals (sugars, organic acids). Single crystals of L-tartaric acid were prepared, further analysed, and optical functions obtained.
Can family language policy predict linguistic, socio-emotional and cognitive child and family outcomes? A systematic review
Multilingual families face decisions about the linguistic upbringing of their children. These decisions shape their family language policy (FLP) which potentially impacts the children and their fam...