Search

We developed a cw laser in the 2 µm region operating at liquid-nitrogen (77 K) and at dry ice temperature (210K) pumped by the 514 µm line of Ar+laser. Also we observed two walenghts (670 mm, 890 mm) that are significantly correlated with laser emission.

A newly developed tunable YLF laser operating in the 2µm wavelength region demonstrates an output power of about 300 mW in a single longitudinal mode, combined with a high spectral purity. It has been employed for measurements of the first overtone spectrum of DCN in a molecular beam with bolometric detection, achieving a signal-to-noise ratio larger than 1000.

There are a number of diseases associated with herpes simplex virus infections, and although there are available treatments, there is still a need for new therapies. Some peptides have proved to have an antiviral effect, but the high flexibility and complex mode of action makes it difficult to obtain reliable quantitative structure–activity relationships. In this article, we report on the use of theoretically derived amino acid descriptors for the modelling of peptide activity as a mean to find lead compounds based on biologically active peptides.

In ion-doped solids there is a nonlinear refractive index n_2 that is due to the polarizability difference Δα between excited and ground states, the so-called population-lens (PL) effect. In addition, the thermal-lens (TL) effect is particularly important in fluoride materials, owing to their low thermal conductivity. We performed time-resolved Z-scan and mode-mismatched TL measurements at λ=488 nm in SrAlF_5:Cr^+3. In this crystal the PL effect is faster than that of the TL, owing to its relatively short metastable lifetime (93 μs), and therefore we could temporally discriminate between these two contributions to the nonlinear refractive index. For the PL effect we measured n_2=(6.6+1.7i)×10^−11 cm^2/W^−1 and calculated Δα=3.1×10^−26 cm^3 and Δσ=?1.7×10^−20 cm^2. From the TL measurements we obtained the thermal diffusivity D=6.5?10^−3 cm^2 s^−1 and estimated the thermal conductivity K=1.7×10^−2 W cm^−1 K^−1 and ds/dT=−8.5?10^−7 K^−1.

We describe the continuous-wave (cw) operation of a LiYF4 laser based on crystals doped with different concentrations of Tm3+. We observed the fluorescence spectra from the upper laser level when the crystal is placed inside the laser resonator, in the same optical environment of the coherent emission. We measured the laser intensity as a function of pump power and obtained a 24% slope efficiency by selecting a suitable orientation of the crystal. Using all this information, we were able to demonstrate laser tunability at 1.9 µm in a 50 cm-1 wide interval.

We report how the photorefractive properties of cobalt-doped barium titanate (BaTiO_3) are influenced by deep and shallow traps. The light-induced dark decay of the space-charge field has two distinct time constants. The faster decay is due to the thermalization of charges from shallow traps, whereas the longer decay is that from deep traps formed when BaTiO_3 is doped with cobalt. This dopant substantially decreases the dark conductivity of BaTiO_3 and thus increases the dark storage time. The power coefficient of the sublinear intensity dependence of the photorefractive response time progressively increases with the cobalt-dopant concentration. Apparently cobalt doping of the deep level eliminates the effect from the shallow level in BaTiO_3. Although cobalt-doped BaTiO_3 has an increased effective trap density and thus an increased electrooptic gain, the response time and absorption are also increased, which thus decreases the photorefractive sensitivity.

Relatively large samples of single crystal barium titanate, BaTiO3, are needed for current photonic applications including for example; optical memories, associative memories and neural networks. The process of producing single-domain crystals called poling usually involves uniaxial pressing to remove orthogonal or 90° domains and then electric field poling to remove antiparallel or 180deg; domains. A method for poling BaTiO3 that significantly reduces the processing time for single-domain sample preparation is described herein. The technique involves the removal, by etching, of surface stresses that mechanically restrict or pin the 90° domains that inhibit their elimination. In this “stress free” state, large volume samples (10 × 10 × 5 mm) are easily electrically poled into single crystals without uniaxial pressing.

Inhibition of electrophoretic cell migration using cerebrospinal fluid (CSF) directly was investigated by the modified MEM (macrophage electrophoretic mobility) and TEEM (tanned sheep erythrocyte electrophoretic mobility) tests, respectively. An inhibitory activity of macrophage slowing factor (MSF)—one of in vivo lymphokines—in CSF was established in cases of multiple sclerosis (17.5±3.8%) and neurolues. The value of this MSF assay turned out to be significantly different from the remaining inflammatory ailments of the nervous system (10.1±6.8%). Results of other neurological diseases were found to be very much lower (5.1±4.2%). It seems important, for immunopathogenesis and the diagnosis of neuroimmunological diseases with enhanced cellular immunoreaction, to evaluate MSF activity in CSF. To characterize the active factor in CSF (and serum) these fluids were fractionated by gel filtration chromatography as well as supernatants from lymphocyteantigen incubation in MS patients. The main activity for inhibition of electrophoretic cell mobility was eluated in the same fraction in these fluids. It could be shown that units have a molecular weight of about 15000 Daltons; this value for MSF lies below those for other inhibitory lymphokines.

With the MEM test (Field) one can establish a cellular immune reaction because the sensitized lymphocytes release the macrophage slowing factor (MSF) upon interaction with the appropriate antigen. A macrophage migration inhibition was detected in some neurological diseases with destruction of the parenchyma. The modification MEM-LAD (linoleic acid depression) test made further differentiation possible in the 146 neurological patients and normals. The reduction of macrophage mobility inhibition was 94.7±4.7% in multiple sclerosis (MS) cases as compared with that of normals of 55.1±3.7% and of other neurological diseases of 47.8±7.1%. There were no significant differences due to the course and duration of the disease or to immunosuppressive therapy. The pathogenically important results in relatives of MS patients with values between the MS and normal group (78.5±0.7%) in mothers suggested a familial (genetic) disposition. The same value was found in a monozygotic twin of an MS patient. The results in the children studied showed that besides the endogenic metabolic component the aetiopathogenically important exogenic factors can operate early in life. In correlation with the principle of the MEM-LAD test the suppressive action of linoleic acid can result in a further therapeutic concept.

In cell-mediated immune processes the products of antigensensitive lymphocytes are detectable as charge-changing lymphokines by means of the cell electrophoretic mobility method (EM test). The improvement of the method concerns the measuring procedures (indicator particle and automation) and the application of specific antigens. The employment of special membrane antigens (3 M KCl extracts) from tissue of normal brain and brain tumors is decisive for further differentiating results. The application of tumor-associated membrane antigens (TAA) from various kinds of brain tumors shows some diagnostically important reaction patterns. Using a common tumor antigen, the TAA-X3 mixture, a (1) characteristic result of general significance for neoplasms can be obtained; in applying the different TAA of brain tumors the findings in EM test point out an (2) organospecific reactivity and/or a (3) histogenetic reaction pattern. The distinct neuroepithelial and mesodermal brain tumors produce predominantly an organospecific reaction and only partly a histogenetical profile. For this type of reactivity to the TAA in brain tumors, a series of factors depending on neuroimmunological specialities are important.

All patients examined [52] with malignant disease of the female genital tract showed lymphocyte reactions to encephalitogenic factor (EF) of more than 10% as measured by the macrophage electrophoretic mobility(MEM)test and its modification (MOD-MEM). Whilst 13 patients with non-malignant disease of the genital tract and 30 normals showed lymphocyte reaction to EF of less than 6%, 4 patients with nonmalignant gynaecological disease gave values above the 10% limit. The lymphocyte reactions of this latter group of patients were discussed with respect to their previous clinical histories. Some of the malignant cases were carcinoma of the cervix in situ so that the MEM test would appear to be of value in the early diagnosis of cancer. The need for caution in the interpretation of results is discussed as well as further possible applications of the technique.

By means of the macrophage electrophoretic mobility (MEM) test the supposed immunosuppressive activity of the pregnancy-associated a2-glycoprotein (pregnancy zone protein) could be demonstrated significantly. Pregnancy sera and sera of nonpregnant women with hormonal contraception containing this pregnancy protein showed an immunosuppressive activity, too. On the contrary, serum of male donors with the blood group AB and human serum albumin had no inhibitory effects. The results suggest that the pregnancy-associated a2-glycoprotein rather influences the afferent limb of the immune response and does not interfere with the activity of the mediator (migration inhibiting factor).

Summary The effects of lymphokines on guinea pig peritoneal macrophages were measured via flow cytometry utilizing the three-parameter FLUVO-METRICELL flow cytometer. On the basis of cell volume three distinct macrophage populations could be distinguished. Three to 5 min after starting the incubation with lymphokines a hyperpolarization of all three macrophage populations took place which was followed by depolarization. After 60 min the transmembrane potential reached again its control values. The negative charge density of the cell membrane decreased shortly after beginning of the incubation to 70-80% of the initial value and then remained unchanged for the following 120 min. The phagocytic activity of the macrophages was diminished during the depolarisation phase but increased over control values after restoration of the transmembrane potential.

A combined familial study of multiple sclerosis (MS) in England and in the Rostock area of the GDR using the macrophage electrophoretic mobility (MEM)-LAD test embracing 132 relatives has revealed a closely similar pattern of distribution of “anomalous” LAD (LInoleic Acid Depression) values in relatives (77% type of reaction) to that originally reported in the British study. The anomaly is predominantly associated with females—all mothers of MS patients being affected, whilst daughters and sisters are also represented. In addition unusual full MS type of reaction (90% reduction) has been found in some children related to patients. There is clearly a genetic element in the development of MS probably manifested in the inborn mishandling of unsaturated fatty acids suggested by Thompson; no recognizable pattern of inheritance is noticeable even within the combined material. There is evidence that the metabolic anomaly alone does not inevitably lead to MS, and the full abnormality may be present at an early age. A survey about the examinations and a selection of characteristic family trees of MS are given, illustrating the manner in which the 77% type anomaly is distributed with occasional omission of a generation.

In an unconventional assay system (MEM Test) Caspary & Field claimed in 1971 to have detected lymphocyte sensitization to a common tumour antigen in all patients with cancer. There was no evidence of histogenetic specificity to the reaction and their conclusions are in direct contradiction to those of all workers who have studied the cytotoxic activity of lymphocytes on tumour cells. To improve the specificity of the test system, another type of tumour antigen was used in MEM Test incubation. Tumour-associated antigens were prepared according to the hypertonic salt extraction method introduced by Reisfeld, Leonard, Meltzer et al. As shown by the results, information could be gained concerning the existence of a malignant tumour and its location.

Room-temperature tunable-laser action has been observed in Cr-doped SrAlF_5. The measured tuning range is 852–947 nm in a quasi-cw laser mode. The effect of nonequivalent Cr sites in SrAlF_5 is studied from the absorption and the excitation spectra. A broad absorption band peaked near 750 nm does not contribute to the Cr emission and appears to be associated with a nonradiative site.

Variably valent iron impurities have been suggested as the source of photorefractive charge carriers in BaTiO_3. High-purity BaTiO_3 crystals were grown with transition-metal impurity levels below the 10^16 cm^−3 baseline estimated for photorefractivity. Iron-doped crystals were grown with concentrations of 5, 50, 250, 500, 750, and 1000 parts in 10^6 of iron. Changes in iron valence monitored by optical absorption in the P_O2 range 1–10^−4 atm were found to be consistent with a defect-chemical model indicating Fe^3+ and Fe^4+ to be the stable valence states in this range. Photorefractive characterization of high-purity BaTiO_3 suggests that variably valent iron ions are not the dominant photorefractive species in these crystals, whereas the role of iron centers in doped crystals is complicated by large absorption losses.

Room-temperature polarized reflectivity measurements are reported for single-crystal La_2CuO_4 for the (E ⊥ ĉ) and (E || ĉ) polarizations, where ĉ denotes the tetragonal axis. A Kramers–Krönig analysis is performed to obtain the frequency-dependent dielectric functions. Frequencies for the seven zone-center IR-active phonons are obtained and the longitudinal-optic–transverse-optic splittings are used to evaluate the dynamic charge on the oxygen atoms. The reflectivity spectrum for the (E ⊥ ĉ) polarization is decidedly metallic and is fitted accordingly with an overdamped Drude model and a plasma frequency of 95 meV. In the high-frequency region of the spectrum, selection rules are observed for allowed and forbidden electronic transitions. The importance of this study to the interpretation of optical measurements on high-Tc, polycrystalline pellets of La_2CuO_4 and related materials is also discussed.

A series of cobalt-doped barium titanate (BaTiO_3) crystals were grown; these crystals have the highest beam-coupling gain reported to date, 7.9 cm^−1, measured by using the smallest electro-optic coefficient of BaTiO_3. The intensity dependence of the absorption and the gain indicate that there are at least two active photorefractive species. These samples show light-induced absorption and negative absorptive coupling, which is indicative of crystals with deep and shallow traps. However, doping with cobalt diminishes the intensity dependence of the electro-optic gain and increases the electro-optic and absorptive coupling, which indicates that cobalt is a deep-level photorefractive dopant. The higher gain is attributed to an increase of the total effective trap density and to an increase in the deep- and shallow-trap intensity-dependent factor η(I), with higher cobalt doping.

Summary With the macrophage-electrophoretic-mobility (MEM)-test (Field and Caspary) specific sensitized lymphocytes can be detected under the condition of a cell-mediated hypersensitivity. The macrophage-slowing-factor—produced by the patients lymphocytes after stimulation with myelin basic protein or similar antigens—inhibits the electrophoretic mobility of macrophages ascertained by the cytopherometer. To point out the value of the method, the lymphocytes of 25 patients with various neurologic diseases were examined. The results showed that during all stages and forms of multiple sclerosis there appeared a distinct inhibition in the MEM-test. Besides the diseases on the base of a delayed hypersonsitivity there were also positive results (>10% inhibition) with the blood-lymphocytes from patients with malignant neoplasm. The detection of malignant tumours in the central nervous system of different kind and localization—like the 39 gynaecological carcinoma comparatively studied—also showed a significant reduction of the macrophage mobility. The diagnostic value of the method is discussed especially with reference to neuroimmunologic diseases and brain-tumours and also to the further possibilities of differentiation.

Energy-transfer processes (including upconversion) are quantitatively studied in a Tm:Yb:BaY_2F_8 laser crystal. Several energy-transfer, cross-relaxation, and upconversion parameters are determined. We prove that at excitation of the crystal via Yb ions, the Tm levels ^3F_4, ^3H_4, ^3F_3, 2, ^1G_4, and ^3P_0 are populated via Yb–Tm interaction, and the level ^1D_2 is likely populated owing to ^3F_3 Tm–^3F_3 Tm upconversion. The possibility of resonant excited-state absorption at 706 nm and resonant energy-transfer upconversion populating the level ^1D_2 are discussed. The possibility of avalanche pumping of Tm:Yb:BaY_2F_8 at 706 nm is shown.

Preparations of allogenous and xenogenous retinal rod outer segments (ROS) were found to be adequately antigenic for detection of cellular immunity in human chorioretinitis.

Rabbits were sensitized intracutaneously with Candida albicans total antigen by a series of booster injections. The electrophoretic migration time of lymph node lymphocytes was related to the time after injection. Two lymphocyte sub-populations could be distinguished. The proportion of each, changed during the course of the immune response. Characteristic changes also took place after in vitro incubation with Candidin. The results have been compared with agglutination titers and are discussed in relation to bursa and thymus-derived cells. The electrophoretic method may be valuable for the diagnosis of candidiasis.

Ferroelectric domain inversion has been demonstrated in BaMgF_4. Transparency has been measured to <140 nm, and no change in transmission was measured under 157-nm irradiation for >1.1×10^9 shots at 2 mJ/cm^2 per pulse. First-order quasi-phase-matched generation of 157??nm is predicted by use of grating periods as long as 1.5 μm. This material should permit shorter-wavelength χ^2 frequency-mixing processes than with any other crystalline material.

Kerr-lens mode-locked Kr-laser-pumped Cr:LiSGaF and Cr:LiSAF lasers containing only two newly developed low-loss chirped mirrors instead of conventional dielectric resonator mirrors and generating pulses of widths as small as 14-fs with as much as 100??mW of average output power are reported. We report what is to our knowledge the first experimental observation of a pulse self-frequency shift in crystalline active media that are characteristic of such short pulses at megawatt intracavity peak powers. We also believe this phenomenon to be one of the significant limiting factors for pulse duration in femtosecond Cr:LiSAF-type lasers.

Efficient high-power (900-mW) TEM_00 cw operation of a Cr:LiSrGaF laser pumped by a Kr^+ laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr^+-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The influence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Laser operation at 2.8 μm in BaY_2F_8 with erbium concentrations of 7.5% and 20% is investigated under laser-diode pumping at 967 nm. Output powers as high as 250 mW and slope efficiencies as high as 24% are obtained. Results are comparable with those of Er^3+:LiYF_4 under the same pump conditions. Slope efficiencies above 30% are predicted for optimized erbium concentrations.

Relatively fast self-pumped phase-conjugate and four-wave-mixing rise times are reported in n-type cobalt-doped barium titanate. With the crystal oriented in a 45° cut as compared with the same crystal in a 0° cut we find a factor of 3 decrease in the 0–90% rise time to 800 ms with 25-mW input power at 514.5 nm. Also, the self-pumped phase-conjugate reflectivity increases from 20% to 40%. We deduce that the phase conjugation is from internally seeded stimulated photorefractive backscattering. The four-wave-mixing rise time of the 45°-cut crystal is 4 ms with a reflectivity of 48% when the pumping beams are derived from self-pumped phase conjugation that has an input power of 25 mW.

We report the beam-coupling properties of a cobalt-doped oxygen-reduced n-type barium titanate crystal in the 0° and 45° crystallographic orientations. Oxygen reduction improved the response time of the 0°-cut crystal by a factor of ~4.5 without diminishing the beam-coupling gain. The 45°-cut crystal has a peak gain of ~38.7 cm^−1, a response time of ~21 ms, and a photorefractive sensitivity of 3.44 cm^3/kJ. We infer from response time measurements an equivalent percentage change in the dc dielectric constant and the mobility with respect to crystallographic orientation.

Kerr-lens mode-locked Kr-laser-pumped Cr:LiSGaF and Cr:LiSAF lasers containing only two newly developed low-loss chirped mirrors instead of conventional dielectric resonator mirrors and generating pulses of widths as small as 14-fs with as much as 100 mW of average output power are reported. We report what is to our knowledge the first experimental observation of a pulse self-frequency shift in crystalline active media that are characteristic of such short pulses at megawatt intracavity peak powers. We also believe this phenomenon to be one of the significant limiting factors for pulse duration in femtosecond Cr:LiSAF-type lasers.

Efficient high-power (900-mW) TEM_00 cw operation of a Cr:LiSrGaF laser pumped by a Kr^+ laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr^+-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

A Kerr-lens mode-locked Cr:LiSrGaF laser containing no intracavity prisms has been demonstrated for the first time to the authors’ knowledge. The laser produced stable near-transform-limited 44-fs pulses with an output power of 200 mW, tunable between 833 and 857 nm. Low-loss Gires–Tournois structured dielectric mirrors were used for dispersion control. The measured group-delay dispersion of the active medium as well as of the mirrors permitted to minimize the number of reflections, permitting higher output power.

We have demonstrated stable and self-sustaining Kerr-lens mode locking of a Cr:LiSGAF laser pumped by AlGaInP laser diodes. A hard aperture near one end of the laser provides the necessary amplitude modulation. This all-solid-state system generates transform-limited 100-fs pulses, tunable from 810 to 860 nm. The average power at 830 nm is 35 mW, with fluctuations of much less than 1%. The thermal properties of Cr:LiSGAF will permit scaling of these results to higher power.

We report the cw laser emission of Ho: YLF in an astigmatically compensated resonator under pumping by a laser diode array. We measured the laser efficiency at different operating temperatures of the crystal and the non-saturated gain coefficient at the peak wavelength of laser emission. The laser tunability extends from 2.040 µm to 2.075 µm.

Broadly tunable laser operation has been obtained at room temperature from the vibronic bands of single-crystal BeAl_2O_4:Cr^3+ under Xe-flashlamp excitation. Continuous tuning is obtained from 701 to 794 nm, with maximum power at 750 nm. Long-pulse operation employing 6.3-mm × 76-mm rods easily provides 500 mJ in 200-μsec bursts, whereas 70-mJ, 120-nsec pulses are obtained under Q-switch operation.