Tunable infrared generation in KTA and applications

Noncollinear difference frequency mixing of dye laser and Nd:YAG second harmonic (fundamental) radiation from a commercial laser system is employed for the generation of 2.7–5.3 μm (1.6–1.7 μm) radiations in a flux-grown KTiOAsO₁ crystal. The generated radiation is used to scan the methane absorption in the fundamental (v ₃) and its first overtone (2v ₃) band at pressure 90 torr in a laboratory made single pass gas cell of length 33 cm.     

Noncollinear folded mixing geometries for difference-frequency far infrared generation

Noncollinear folded geometries for far infrared generation by difference-frequency mixing of CO₂ lasers are analyzed, and are shown theoretically to provide orders of magnitude increase in the far infrared output compared with the simple noncollinear geometry used previously. The basic principle of the folded geometry has been verified experimentally.     

Tunable infrared difference-frequency generation with a high-repetition pulsed dye laser

An output from a cresyl-violet dye laser, pumped by the second harmonic of a Q-switched Nd:YAG laser, is mixed with the pumping light in a LiIO₃ crystal to produce an infrared output tuned from 2.8 to 3.4 μm with a repetition rate of 20 pps.     

Tunable infrared generation using the 6s−5d Raman transition in caesium vapour

Coherent infrared radiation tunable between 1.6 and 3.2 μm was generated with a pulsed dye laser by 6s−5d _5/2 stimulated electronic Raman scattering in caesium vapour. We describe a technique using thermal dissociation to reduce the density of caesium dimers in a heat-pipe oven, which produced a factor of 7 reduction in Raman threshold. The threshold displayed a marked dependence on pump bandwidth.     

Tunable infrared down-conversion in silver thiogallate

A ruby laser beam mixed in AgGaS₂ with the output of various ruby-pumped dye lasers has provided down-converted infrared radiation tuned from 4.6 to 12 μm. The measured phase-matching angles agree well with calculated values. Peak infrared powers of a few hundred milliwatts have been produced.     

Tunable laser-sideband generation in InSb

The resonant third order non-linear susceptability in InSb has been employed to generate a magnetically tunable cw laser sideband near 5 μm.     

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO₂ lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO₂ lasers. Using the combination of lines from a waveguide CO₂ laser, with its larger tuning range, with lines from CO₂, N₂O, and CO₂ isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm^–1) with stepwise-tunable cw radiation.Contribution of the National Bureau of Standards, not subject to copyright     

Tunable gamma ray generation

In this note, we wish to point out that utilizing presently available technology it is possible to construct an intense, modulated and polarized γ-ray source which can be used for spectroscopy purposes to good advantage.     

Tunable far-infrared Raman generation

Tunable resonance enhanced far-infrared stimulated Raman scattering was observed in 60–160 μm range for the Q(J) transitions in hydrogen chloride. The tuning range was about 2.3 cm^-1 around each studied transition (J = 2 to 7) and the photon efficiency was measured to be of the order of 12% giving peak power around 80 kW.     

Thermography: Imaging in the far infrared

Thermography, the art of visualizing and interpreting thermal patterns, is a versatile new tool for science, medicine and technology. It is developing rapidly and spreading into widely diverse fields. Although its origins are more than 130 years old, the first practical applications (in military reconnaissance) were achieved only 15 years ago. Today, clinical thermography offers new hope in the fight against cancer, and has many other uses; it is a completely passive diagnostic method and absolutely safe. In industry, thermography has potential value whenever there are problems in measuring temperature over extended areas, where point contact methods are insufficient, tedious, or impossible (e.g. in inaccessible places). Thermographic microscopes and telescopes offer great possibilities which are only just beginning to be explored. The design of thermographic equipment presents problems which do not arise in most electro-optical systems, including television, and which more nearly resemble the design problems of radio telescopes. This article reviews the basic principles and the design optimization of thermographic scanners.     

Tunable upconversion in Er-doped orthorhombic lead fluoride compound

Near infrared-visible upconversion in Er³⁺ doped orthorhombic PbF₂ compound is investigated. It is experimentally observed that the red emission intensity increases monotonously with Er³⁺ concentration increase, while the green emission intensity first increases and then decreases. Based on the rate-equation, the energy transfers involved in the upconversion processes have been explored. It is shown that due to the different multipolar nature for the energy transfer processes of ²H_11/2 (⁴S_3/2)+⁴I_15/2→⁴I_9/2+⁴I_13/2 and ⁴I_11/2+⁴I_11/2→⁴F_7/2+⁴I_15/2, the green and red upconversion emissions depend on Er³⁺ concentration in different ways. The theoretical results are in good agreement with the experimental observation. It is shown that the upconverted emission bands can be tuned by controlling Er³⁺ concentration in orthorhombic PbF₂ compound, which has many photonic applications under NIR excitation.     

Optical properties of barite in the infrared and far infrared ranges

Far infrared and infrared reflectivity was measured for barite single crystal using polarized light. Twenty six oscillators were observed. The real and imaginary parts of the complex dielectric function were obtained by a fitting procedure for three directions (E a;E b andE c). Group theory analysis has been done in detail and the number and position of experimentally observed infrared active modes were compared with the theoretical predictions.     

Phonon-polariton meta-atoms for far infrared range

Polarizabilities of spherical subwavelength silica glass particles are investigated having regard to material dispersion. It is shown that the ranges of the negative electric and magnetic polarizabilities almost coincide. This allows the particles in question to be used for producing media with a negative refractive index.     

Classical treatment of the dissociation of hydrogen fluoride with one and two infrared lasers

Classical mechanics is used to show that hydrogen fluoride may be more easily dissociated with two infrared lasers of different frequencies than with just one. It is shown that the two laser dissociation proceeds by a qualitatively different process than the one laser dissociation.     

Lattice absorption of Ge in the far infrared

The lattice absorption at low frequency (100 cm⁻¹) and low temperature (50 K) of Ge is very small, yet it may influence the performance of the p---Ge hot hole far-infrared laser. We have measured by temperature-tuned laser interferometry.     

Measurement of solar temperature in the far infrared

We have measured the temperature of the Sun in the 300–1000 μm region through the atmospheric windows at the high altitude observatory of Testa Grigia, Italy. 3500 m a.s.l. The far i.r. detector used in this experiment is a 150cm flux collector with a germanium bolometer. A set of interferential filters coupled to a specially designed radiometer allow us to isolate and measure the atmospheric windows transmittance with a precision of 1 per cent. The results obtained are in agreement with the HSRA model of the Sun.     

Paper sheet moisture measurements in the far infrared

Measurement of several parameters pertinent to process and quality control in the manufacture of paper products is a potentially important application of far-infrared lasers. Preliminary measurements of the transmittance and reflectance of moist paper sheets are presented, and their use to determine the percentage moisture content and the dry basis weight of the paper is discussed.     

Subnanosecond optical switching of far infrared radiation

Switching of 119 μm CH₃OH laser radiation in less than 1 ns was achieved by irradiating high resistivity Si (>10⁴ Ω cm) and GaAs (>10⁷ Ω cm) samples with 1.4 ns, 150 μJ pulses from a 337 nm TEA nitrogen laser. Modulation degrees of up to 100% were observed both in reflection and transmission.     

The far infrared complex reflectivity of GaTe

The room temperature polarized complex (amplitude and phase) infra-red reflection spectra of single crystal monoclinic GaTe have been measured between 20 and 400 cm^–1 using a dispersive Fourier transform spectrometer. The measurements allow the experimental zone centre transverse and longitudinal phonon modes and optical constants to be determined without recourse to oscillator fit models or Kramers-Kronig analysis. Infrared power transmission measurements have allowed all fifteen predicted modes to be identified and the results are compared to recent Raman work.