Optically-pumped Far-infrared Laser Research Articles

Discovery of Optically Pumped Far-infrared Laser Emissions from Formic Acid and its Isotopologues

An optically pumped molecular laser system with a transverse excitation scheme has been used to generate far-infrared radiation. Over 100 laser emissions with wavelengths up to 1.03 mm have been detected with this system using formic acid and several of its isotopologues. This includes ten new laser lines which are reported with their operating pressure, power, polarization with respect to the CO2 pump laser, and wavelength measured to an uncertainty of ± 0.5 μm.

Spatio-temporal theory of lasing action in optically-pumped rotationally excited molecular gases

We investigate laser emission from optically-pumped rotationally excited molecular gases confined in a metallic cavity. To this end, we have developed a theoretical framework able to accurately describe, both in the spatial and temporal domains, the molecular collisional and diffusion processes characterizing the operation of this class of lasers. The effect on the main lasing features of the spatial variation of the electric field intensity and the ohmic losses associated to each cavity mode are also included in our analysis. Our simulations show that, for the exemplary case of methyl fluoride gas confined in a cylindrical copper cavity, the region of maximum population inversion is located near the cavity walls. Based on this fact, our calculations show that the lowest lasing threshold intensity corresponds to the cavity mode that, while maximizing the spatial overlap between the corresponding population inversion and electric-field intensity distributions, simultaneously minimizes the absorption losses occurring at the cavity walls. The dependence of the lasing threshold intensity on both the gas pressure and the cavity radius is also analyzed and compared with experiment. We find that as the cavity size is varied, the interplay between the overall gain of the system and the corresponding ohmic losses allows for the existence of an optimal cavity radius which minimizes the intensity threshold for a large range of gas pressures. The theoretical analysis presented in this work expands the current understanding of lasing action in optically-pumped far-infrared lasers and, thus, could contribute to the development of a new class of compact far-infrared and terahertz sources able to operate efficiently at room temperature.

Electric field effect on the optically-pumped far-infrared laser

This study investigates the effects of the electric field on the optically-pumped far-infrared (OPFIR) laser. The main mechanisms responsible for the change of the laser output power due to the electric field are considered to be the non-linear Hanle effect (NLHE) and Stark splitting. However, both the rate-equation calculation and the experiments with the circular hollow Stark waveguide OPFIR laser show that the conventional NLHE provides a relatively limited power increase via enhanced absorption. Significant power enhancement is observed in the rectangular waveguide only when both the absorption and emission processes are ΔM=±1 transitions, where the classical Hanle effect (CHE) is considered to be applicable. By including constructive interference, the power increase due to the CHE is calculated for the parallel and orthogonal lines. Experimental results from the rectangular waveguide OPFIR laser show good agreement with the new calculation taking into account the classical Hanle and Stark splitting effects.

使用热释电相机进行实时连续波太赫兹成像的研究

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped far-infrared laser is used as the illumination source, and a 124×124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.

A Revisory Mathematical Model on Optically Pumped Far-Infrared Laser

In an optically pumped far-infrared laser (OPFIRL) system, the infrared (IR) pumping laser with collision broadening which was closer to the practice was considered. A more precise mathematical model was set up. When the IR pumping laser line had the Lorentz function structure, by solving the semi-classic density matrix equations, the generalized form of FIR signal gain Gs and IR pumping signal absorption coefficient Gp were obtained.

Theoretical Study on NH3 Superradiant Miniature Optically Pumped Far-Infrared Laser with Buffer Gas

A miniature superradiant NH3 optically pumped far-infrared laser (OPFIRL) with buffer gas N2 was theoretically studied. Base on the mechanism model of buffer gas, synthetical relaxation time was calculated. By solving the semi-classic density matrix equations, spectra of NH3 superradiant OPFIRL with buffer gas N2 was calculated, also the operating gas pressure. It was found that by adding buffer gas, FIR power could be raised, and there existed an optimum ratio of gases mixture and an optimum operating gas pressure which was higher than that of pure NH3 operating.

Energy Exchanged Process of Superradiant Optically Pumped Far-Infrared Laser with Buffer Gas

By means of solving the density matrix equations, base on the mechanism model of buffer gas, the output intensity of FIR and the FIR signal gain coefficient Gs and IR pumping signal absorption coefficient Gp were calculated, energy exchanged process of superradiant OPFIRL with buffer gas was analyzed. It was found that after adding buffer gas into the laser medium, the FIR output could be increased, and the active region of a FIR laser was lengthened.

A New Model of Calculating Miniature Optically Pumped Far-Infrared Laser

Considering the broadening of infrared pumping laser, the spectrum of miniature optically pumped superradiant NH3 far-infrared laser pumped by CO2-10R(8) has been calculated by solving density matrix equations and using iteration method. It is first time that the theoretical spectrum has been in good agreement with experimental results.

Optically Pumped Far-Infrared Laser Lines in Hydrazine, Methanol, Heavy Water, and Ammonia: New Laser Lines and Frequency Measurements,

A far-infrared laser cavity designed to favor short-wavelength laser lines was used to generate optically-pumped far-infrared laser radiation. New far-infrared laser lines were discovered in hydrazine, heavy water, ammonia, and several short-wavelength lines previously discovered in methanol were observed. Wavelength, frequency, and relative intensity measurements were performed on laser lines in the wavelength range 42.4 to 253.7 μm. Each far-infrared frequency measurement was obtained by mixing the far-infrared radiation with radiation from two reference CO2 lasers and from a microwave synthesizer in a metal-insulator-metal diode. The pump laser was a high-Q Fabry Perot resonator oscillating on 275 grating-selected laser lines including regular, sequence, and hot band lines.

New Optically Pumped FIR Laser Lines and Frequency Measurements from CH3OD

This work reports the discovery of 45 new optically pumped far-infrared (FIR) laser lines from CH3OD in the range 42.6 μm to 207.2 μm. A highly efficient CO2 laser was used as the pump laser for an Optically-pumped Fabry-Perot FIR laser. The frequencies of most of the new lines were measured in the range 1.7 to 6.4 THz. Twenty-eight CO2 lines were used as pump lines; nineteen of these had frequencies lower than those previously used to pump CH3OD in a FIR laser. Sixteen of the new FIR lines had absorption transitions which belong to the OD bending vibrational mode.

Low frequency noise optically pumped FIR laser with frequency stabilized pump

A new method of frequency stabilization of the pumping laser of an optically pumped far infrared laser (OPFIRL) has been developed. With the frequency of the pump stabilized in this way the phase noise of the OPFIRL is minimized and the laser can remain phase locked to a hydrogen maser for several hours. A measurement of the spectral density of phase noise of the generated submillimetric radiation at 716 GHz is reported; to our knowledge this is the first time that a measurement of phase noise, using a mixer as phase discriminator, is performed in the submillimetric domain.

Polarization modulation in an optically-pumped far-infrared laser

Measurements performed on intracavity polarization modulation in an optically-pumped far-infrared laser are presented. The experimental work is a preparatory first step towards the development of a polarimeter diagnostic system for plasma physics applications. The present system utilizes a CO 2 laser whose output polarization state is modulated using a CdTe crystal placed within a sinusoidal magnetic field. The corresponding polarization modulated amplitude of the far-infrared output is determined, and the results obtained are in good agreement with the Verdet coefficient of CdTe previously reported.

Application of high-resolution Fourier transform spectroscopy to Fermi resonance and the assignment of far-infrared laser lines in CD 3OH

High-resolution Fourier transform spectra of the infrared (IR) CO stretch band and the farinfrared (FIR) torsion-rotation band of CD 3OH have been analyzed to find new assignments of reported optically-pumped FIR laser lines and to confirm previous assignments proposed by other workers. The identified CD 3OH FIR laser emission includes a substantial group of transitions involving CO stretch levels which are significantly shifted by Fermi resonance with high-lying torsional levels of the vibrational ground state. The results are supported by frequency combination relations for closed IR FIR transition loops, which also yield improved accuracies for a number of observed or predicted FIR laser frequencies. The previous assignments have generally been confirmed, with modifications for two of the pump systems. Offsets of the assigned IR pump transitions from the corresponding CO 2 laser lines are also presented, as determined from the spectroscopic data.

Phase dynamics in a Doppler broadened optically-pumped laser

The dynamic behavior of the phase of the generated field in a Doppler-broadened optically-pumped far-infrared laser is theoretically investigated for the first time. The phase undergoes sudden jumps of approximately π radians, which allow to establish the actual symmetry of the main attractor in the phase space, explaining the heteroclynic character of the chaotic behavior observed in experiments.

Lorenz-like dynamics in Doppler broadened coherently pumped lasers

We report the theoretical interpretation of Lorenz-like behavior recently observed for the first time in a laser by Weiss and Brock [Phys. Rev. Lett. 57 (1986) 2804]. By means of a three-level laser model it is shown that in an optically-pumped far-infrared laser, coherent pumping effects are partially smeared out by Doppler broadening and as a result Lorenz-like dynamics may show up in some physical observables such as laser intensity.

The conditions for Lorenz chaos in an optically-pumped far-infrared laser

The conditions for Lorenz chaos in cw optically pumped far-infrared (FIR) lasers are more stringent than those derived in two level systems due to the pump laser induced coherence. We list a set of six conditions which should be fulfilled in order to observe Lorenz chaos. The main new requirement is a fast relaxation of the off-diagonal elements involving the ground rotational molecular level. We propose the use of a chaotically emitting pump laser in order to avoid the induced coherence effects. By comparison with the standard mode of operation, useful insight into the coherent dynamics of optically pumped lasers could be gained.

Radio-frequency Stark tuning of optically pumped far-infrared lasers

We have directly monitored the rf Stark-field-induced splitting of the gain profile of the 1222-microm (13)CH(3)F optically pumped far-infrared (OPFIR) laser transition. The resulting data are found to be in good agreement with ac Stark theory. Comparison with dc Stark tuning techniques shows that the rf Stark effect possesses a number of attractive attributes for frequency tuning cw OPFIR lasers, including significant increase in the turing range and straightforward implementation.

Measurement of far-infrared optical constants by ATR

Using an optically-pumped far-infrared laser as a light source, the far-infrared optical constants of liquid acetonitrile, methanol, dichloromethane, and chlorobenzene were obtained by measuring the attenuated total reflections of light for two mutually perpendicular polarizations. The ATR prism of hyper-pure silicon was made asymmetric to avoid the effect of the multiple reflection inside the prism.

Photon-assisted tunneling and AC Josephson effect at 246 and 604 GHz in small-area superconducting tunnel junctions

We report the first observations of photon-assisted quasiparticle tunneling and AC Josephson effect in superconducting tunnel junctions irradiated with far-infrared (FIR) radiation. Radiation at 246 GHz (λ=1.22 mm) and 604 GHz (496 μm) from an optically-pumped FIR laser source was used. Tin-tin oxide-lead junctions of ∼1 (μm) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area were fabricated on crystal quartz substrates with integral planar dipole antennas of resonant length at the frequency of the incident radiation. The observed photon-assisted tunneling features are in excellent agreement with the Tien-Gordon theory, and the inferred responsivity approaches the quantum limit at low temperatures for photon energies less than the gap. At 604 GHz, with a 176 ohm junction, we have seen 7 Josephson steps, comparable to point contact performance. The variation of the step widths with laser power is found to agree quite well with both the RSJ model and the Werthamer theory. For low resistance junctions (e.g. 16 ohms), we find the Josephson steps to be flat and to agree well with the shape predicted by the RSJ model without noise rounding, while noise rounding is very evident with the higher resistance junctions. In all cases, the step shape is in reasonable agreement with the theory of P. A. Lee, using a noise temperature of 10-20K with an appropriate small junction capacitance.

Application of an Optically-Pumped Far-Infrared Laser to the Study of the Josephson Effects

Application of an Optically-Pumped Far-Infrared Laser to the Study of the Josephson Effects