The use of infrared up-conversion for the detection of 1.3 μm luminescence

Conversion of IR radiation with λ=1.3 μm into the visible by use of nonlinear sum-frequency mixing in a LiIO₃ crystal was studied experimentally. Advantages and disadvantages of the up-conversion method compared with other methods for NIR-light detection are discussed. The results of the present study can be useful for time-resolved nonlinear up-conversion of the weak luminescence signals.     

Tunable UV and IR picosecond pulse generation by nonlinear mixing using a synchronous mode-locked dye laser

The short-pulse output from a synchronous mode-locked tunable dye laser was sum and difference mixed in nonlinear crystals of KDP, ADP and LiIO₃ with the 1.064-μm and 532-nm pulse trains from its mode-locked Nd: YAG pump. This method allowed efficient generation of narrow-bandwidth tunable short pulses in the uv from 270 to 432 nm and in the IR from 1.13 to 5.6 μm.     

Generation of tunable cw infrared radiation by difference frequency mixing

Tunable cw infrared radiation has been generated by noncollinear difference frequency mixing in LiIO₃, using the output of an argon ion laser at 514 nm or 488 nm and the intracavity radiation of a Rhodamine 6 G dye laser. Infrared powers up to 4 μW in multimode and 0.5 μW in single-mode operation tunable in the range of 2.3 μm to 4.6 μm have been obtained. Properties and possibilities of the noncollinear mixing geometry and the intracavity mixing system are discussed.     

Frequency doubling of cw ring-dye-laser radiation in lithium iodate crystals

We report on frequency doubling of cw ring-dye-laser radiation in lithium iodate crystals (LiIO₃). The conversion coefficient and the matching angle were measured as a function of the fundamental wavelength in the range 586.3–624 nm. For Type I phasematching the matching angle _m=90° for noncritical matching was found at 586.3 nm. At this wavelength the conversion coefficient reaches the maximum value which was observed to be as high as 1.6×10^–2 W^–1 for a LiIO₃ crystal of 1 cm length. From the dependence of the matching angle on the wavelength the refractive induces were determined for the ordinary as well as for the extraordinary ray in the wavelength range from 293 nm up to 355 nm. The influence of focussing on the conversion coefficient is discussed.     

Pulsed infrared radiation transmission through chalcogenide glass fibers

Two different kinds of chalcogenide glass IR fibers were evaluated relative to transmission of pulsed IR radiation produced by several laser sources in the wavelength range from 1 to 10 μm. Fibers composed either from As-Se-Te or from As₂S₃ glass, of 250, 500, 750 and 1000 μm and 250, 750 and 1000 μm core diameters were studied, respectively. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, wherever this was possible. The output beam quality was also studied using a beam profiler. The lasers used were a Q-switched Nd:YAG laser, emitting at 1.06 μm, a free-running or Q-switched Er:YAG laser emitting at 2.94 μm and a tunable pulsed CO₂ laser emitting in the range of 9.3-10.6 μm. The fibers exhibited better behavior when tested with the Er:YAG laser and they were found fragile in pulsed radiation from the Nd:YAG and the CO₂ laser. The output beam profiles generally showed a central multi-spiking energy distribution.     

Continuum radiation from the mercury arc

Independent, quantitative measurements of continuum radiation from mercury arcs have been made at our separate laboratories and the Abel-inverted emission coefficients analyzed together. Continuum at selected wavelengths (free of atomic lines) between 0.4 and 1.3 μm were included at mercury pressures of 0.1, 1.0 and 2.7 atm. Equilibrium vapor compositions were calculated for the measured radial temperature profiles. The temperature dependence of the continuum emission was used to separate it into components from electron-Hg⁺ recombination, electron-neutral Hg⁰ bremsstrahlung and Hg₂ molecular radiation. Electron-neutral bremsstrahlung is particularly strong because of the large electron scattering cross section of mercury and low fractional ionization making quantitative comparison with theory possible. Our results for this interaction are in good agreement with recent theoretical calculations of S. Geltman at 1.0 μm but ≈3 times the theoretical value at 0.5 μm.     

Determination of IR radiation attenuation in chalcogenide glass fibres by tunable diode lasers

Lead-salt tunable diode lasers were applied to measure IR attenuation in As₂Se₃ chalcogenide glass fibres. The attenuation constant at 10.5 μm is determined from the slope of the IR transmission through a fibre as a function of its length, and the spectral dependence over the 10–13 μm wavelength region is obtained by tuning the laser IR source.     

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.     

Non-collinear phase matched 4-wave mixing of CO2 and NH3 laser radiation in germanium

4-wave mixing has been demonstrated in room temperature germanium using a TEA CO₂ laser (9.3 μm) and an optically pumped NH₃ laser (12.8 μm) as radiation sources. Non-collinear phase matched emission near 7 μm has been observed with a mixing efficiency close to the calculated value. The extension of this mixing process to generate wavelengths in the important region near 16 μm is discussed.     

Filtration of IR radiation by three-component polymer-crystalline systems

We have investigated the regularities in forming the spectral characteristic of three-component polymeric-crystalline polytetrafluorethylene-Ge-LiF interference systems in the wide IR spectral region 0.8–160 μm. The efficiency of suppressing short-wave radiation by structurally asymmetric imerference systems consisting of polytetrafluorethylene and quasihomogeneous layers with a high refractive index is shown. Two of this kind of three-layer systems are sufficient for suppressing background radiation within the wavelength interval from the visible range to ∼35 μm owing to multiple reflection at the boundaries of elementary Ge and LiF layers that form quasihomogeneous layers (λ ∼ 1.7–17.0 μm) and also due to absorption in the Ge (λ<1.7 μm) and Lif (λ ∼ 17–35 μm) layers. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No_ 3, pp. 379–381, May–June, 2000.     

Effect of magnetic field on the IR optical properties of dielectrics

Magnetic-field induced changes revealed in reflectance spectra R(λ) of nonmagnetic dielectrics Al₂O₃, LiF, and MgO in the IR range (λ = 2.5–25 μm) are reported. The reflectance spectra are shown to have specific features in the vicinity of the wavelengths corresponding to optical phonon mode excitation in these crystals, with the magnetic field giving rise to a noticeable change of reflectance ΔR/R(λ) at these wavelengths. The value of ΔR/R(λ) for p-(s-) polarized IR radiation in a magnetic field of ～13 kOe is ～0.6% (～0.4%) for Al₂O₃ at λ ≈ 9.6 μm, ～1.63% (～1.15) for LiF at λ ≈ 11.1 μm, and ～ 0.07 (～0.2%) for MgO at λ ≈ 11.7 μm, respectively. These changes can be increased substantially by irradiating the dielectric crystals by x-ray radiation. It is shown that the optical and magnetooptical properties of the above dielectrics in the IR spectral region can be described in terms of the polaron excitation theory.     

Growth and spectral-luminescent study of SrMoO<Subscript>4</Subscript> crystals doped with Tm<Superscript>3+</Superscript> ions

SrMoO₄ crystals doped with Tm³⁺ ions have been produced from a melt using the Czochralski method; their spectral-luminescent characteristics have been studied, and laser radiation has been generated at the wavelength of 1.94 μm using laser-diode excitation. The high absorption section at the wavelength of 795 nm, the fairly high luminescence section, the long lifetime at the upper laser level ³F4 of 1.5 ms, and a wide luminescence band allow one to hope for developing efficient tunable Tm³⁺: SrMoO₄ crystal lasers with diode pumping in the range of 1.7–2.0 μm, which are capable of implementing SRS self-transformation of radiation into the middle IR band.     

Noncollinear phase-matched four-photon mixing of CO2 laser radiation in germanium

Noncollinear four photon mixing of two TEA CO₂ laser beams in germanium at room temperature has been used to obtain phase-matched generation of step tunable radiation in the 8.7 μm region which is of interest for the uranium isotope separation. Using an 8.3 cm long crystal of germanium, peak output power of ≈10kW (corresponding to 1 mJ per pulse) was obtained at 8.7 μm with 3 MW peak input power from each of the two CO₂ lasers operating at 9.6 μm and 10.6 μm.     

Resonant transition radiation in the X-ray region from a low emittance 855 MeV electron beam

The interference of transition radiation coherently produced from a periodic stack of four polyimide foils of 7.2 μm thickness and a separation of 162 μm was investigated. This stack has been brought into the low emittance (3 π nm rad) electron beam of the 855 MeV Mainz Microtron MAMI. Transition radiation was observed in the energy range from 2 to 15 keV with a LN₂-cooled pin photodiode. A good energy resolution of 0.8 keV and angular resolution of 0.15 mrad was achieved simultaneously allowing for the first time to quantitatively study the interference pattern. Good agreement with theoretical calculations is found. Prospects to exploit transition radiation in the x-ray region from a low emittance electron beam as a high brilliant radiation source are discussed.     

LiIO3-NaIO3赝二元系相图及其非晶态晶化动力学的研究

本文对LiIOO₃-NaIO₃赝二元系的相图,相变,非晶态的形成和稳定性,以及晶化的动力学过程等进行了仔细的研究,LiIO₃-NaIO₃赝二元系属共晶体系,共晶温度为325℃,共晶点成份为含50m/o LiIO₃,用共晶点附近成份的试样,在超过熔点150℃的情况下首次获得碘酸盐的非晶态,非晶态的存在降低了LiIO₃的表观相变温度,强X射线的辐照,各种空气湿度,细粒度等因素都加 关键词：     

Tunable cw infrared radiation by noncollinear difference-frequency mixing

Tunable cw infrared radiation has been generated by non-collinear difference-frequency mixing in LiJO₃, using the intracavity radiation of a Nd:YAG laser and the output of a Rhodamine 6G dye laser. Infrared powers of ∽35 μW tunable from 1.28 μm to 1.62 μm have been obtained.     

Development of coherent tunable source in 2–16 μm region using nonlinear frequency mixing processes

A very convenient way to obtain widely tunable source of coherent radiation in the infrared region is through nonlinear frequency mixing processes like second harmonic generation (SHG), difference-frequency mixing (DFM) or optical parametric oscillation (OPO). Using commonly available Nd:YAG laser and its harmonic pumped dye laser radiation as parent beams, we have been able to generate coherent tunable infrared radiation (IR) in 2–16 μm region using different nonlinear crystals by DFM and OPO. We have also generated such IR source in the 4–5 μm region through SHG of CO₂ laser in different infrared crystals. In the process we have characterized a large number of nonlinear crystals like different borate group of crystals, KTP, KTA, LiIO₃, MgO:LiNbO₃, GaSe, AgGaSe₂, ZnGeP₂, AgGa_1?x In _x Se₂, HgGa₂S₄ etc. To improve the conversion efficiencies of such frequency conversion processes, we have developed some novel schemes, like multipass configuration (MC) and positive optical feedback (POF). The significance of the obtained results lies in the fact that to get the same conversion in SHG or DFM, one now requires fundamental input radiation with much lower intensity.     

Dissociation of CF<Subscript>2</Subscript>HCl molecules by intense radiation from a femtosecond laser in the near-IR range

It is found that CF ₂HCl molecules dissociate under irradiation by high-intensity pulses of femtosecond radiation (λ=1.8 μm) in the vicinity of resonance with the frequency of overtone vibrational transitions in the C-H bond. It is shown that the dissociation products substantially differ from the products of dissociation of CF₂HCl molecules from the ground and excited electronic states under the action of IR and UV nanosecond pulses.     

Stimulated Raman conversion of radiation from a YAG:Nd laser with wavelengths of 1.319, 1.338, and 1.357 µm in a barium nitrate crystal

We have studied stimulated Raman (SRS) conversion to the first Stokes component of multimode (M₂ = 8) radiation from a YAG:Nd laser with lasing wavelengths of 1.319 μm, 1.338 μm, and 1.357 μm in a barium nitrate crystal. We have obtained pulses of converted radiation with energies up to 120 mJ. We have achieved conversion efficiencies greater than 40% for each of the three Raman laser wavelengths of 1.530 μm, 1.556 μm, and 1.582 μm with divergence of the beams of converted radiation close to the diffraction-limited value (M₂ < 1.5). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 330–334, May–June, 2006.     

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.