Results of experimental investigation of photoelectric properties of GaAs p-n-junction illuminated by short laser pulses of 1.06 μm wavelength are presented. The influence of laser radiation intensity and external bias voltage on the formation of photoresponse voltage has been studied. Free carrier heating was recognized to influence significantly the magnitude of the measured photovoltage. Possibility to improve the conversion efficiency of solar cells is discussed.
The phase change caused by excitation of surface plasmons (SP) in a Kretschmann configuration was measured by a
rotating polarizer scheme using commercial spectral ellipsometer (GES5, SOPRA, Co). The setup was used to
determinate the optical constants at 800 nm of an octadecanthiol (ODT) with a thickness of 9 nm on a gold film. The
numerical values n=0.18, k=3.44 for the Au film, and n=1.4 for ODT were obtained by a best-fit procedure to
experimental data. From model calculations it is argued that in thin-film cases SP phase measurements give more precise
values for the optical constants than conventional ellipsometry and SP amplitude methods. Combination of SP method
with advantages of phase measurements of ellipsometry showed sufficient increase in sensitivity (more than one order of
magnitude). This methodology could be used for detection of monolayer and even submonolayer films on metals.
In our previous work was showed that the SPR technique is very effective for in situ observation of the lipase interaction
with MNFcP (9 merkaptononyl - 5' - ferrocenylpentanoate). However, the investigation was performed with only
monochromatic 633nm light at the beginning and at the end of the reaction. In this work, the results of the investigation
of the reaction kinetics using a tunable light source (&lgr;=600÷1400nm) are presented. Spectral measurements were
accomplished with a commercial spectral ellipsometer GES-5 (SOPRA, France). It was demonstrated that this method is
sufficiently sensitive for lipase interactions with a thin MNFcP layer (d=3.65nm). It was concluded that the experimental
plasmon minimum shift is due to lipase sorption on the MNFcP and, as a result, causes an increase in the effective layer
thickness. These results are important in understanding the interaction of these molecules and in determing their size and
distribution on the surface.
We describe all solid state differential absorption lidar (DIAL) based on the mid-infrared (IR) tunable Optical
Parametric Oscillator (OPO). Generation of tunable mid-infrared laser radiation using a two stage tandem OPO was
demonstrated. The first stage was based on the nonlinear KTP crystal and produced up to 45 mJ of 1.57 μm radiation,
while pumped by a commercial Q-switched Nd:YAG laser. The quality of signal beam was improved by the use of
unstable resonator. The AgGaSe<sub>2</sub> crystal was used in the second stage OPO. Idler energies up to 1 mJ were generated at
this stage within tuning range from 6 to 12 μm. The receiver consisted of a 250 mm gold mirror telescope, two channel
detection system and control electronics. We have designed a photoacoustic cell for wavelength calibration of lidar.
Preliminary lidar field test results are presented.
We present the second phase of our work in project LISATNAS devoted to design the differential absorption lidar (DIAL) based on the mid-infrared (IR) tunable Optical Parametric Oscillator (OPO). Generation of tunable mid-infrared laser radiation using a two stage tandem OPO was demonstrated. The first stage was based on the nonlinear KTP crystal and produced up to 45 mJ of 1.57 μm radiation, while pumped by a commercial Q-switched Nd:YAG laser. The quality of signal beam was improved by the use of unstable resonator. The AgGaSe2 crystal was used in the second stage OPO. Idler energies up to 1.2 mJ were generated in this stage within tuning range from 6 to 12 μm. The receiver consisted of a 250 mm gold mirror telescope, pyroelectric detector with control electronics. Preliminary field test results for detection of H<sub>2</sub>O using a retroreflector are presented.
We describe a new development of differential absorption DIAL spectrometric system based on the mid-infrared tunable Optical Parametric Oscillator (OPO), pumped by compact Q-switched lasers. Mobile LIDAR was assembled in the truck and is devoted for selective pollutant analysis in the distance range extending from hundred
of meters to a few kilometers. A reliable cascade mid-IR generation scheme was developed. Pulse energies up to milijoule in mid-IR (λ=8-12 μm) have been already obtained using nonlinear AgGaSe<sub>2</sub> crystal. The collinear optical scheme with 25cm (10inch) gold mirror telescope, MCT thermoelectrically cooled detector with control electronics was tested at 250m optical length and currently is under further development.
High sensitivity and selectivity of gas/vapour detection are achieved employing registration of laser photoacoustic spectra. The lasers are usually operated in the continuous-wave (CW) single-frequency mode. The tuning range of the single CW laser system is not sufficient to cover spectral bands of variety of gases/vapours of interest. The optical parametric oscillator (OPO) systems are more preferential for multi component laser analyzers allowing the simultaneous measurement of different gases or pollutants. Pumped by the same 7 ns duration pulse of Nd:YAG laser and its harmonics, two OPO systems were tested. One system generates in the 0.7-1.9 μm range and covers overtones of stretching vibrations and combination vibrations of hydrogen atoms in the analyte molecule. Other system generating in the 5-11 μm range covers vibrations of molecular characteristic groups ("fingerprints"). Photoacoustic spectra of nitro compound vapours, e.g. nitromethane, nitroethane, nitropropane, nitrobenzene and nitrotoluene, also spectra of methane and water vapour were measured and compared to simulated spectra derived with the aid of HITRAN data base and to the literature spectral data. Photoacoustic detection thresholds are evaluated from the ratios of measured signal to the registration noise.
We describe a new project (acronym LISATNAS) approved by the Lithuanian Research Council in 2003 devoted to the development of differential absorption lidar (DIAL) and stationary spectrometric systems based on the mid-infrared tunable Optical Parametric Oscillator (OPO), pumped by compact Q-switched lasers. The purpose of the project is to construct a mobile infrared lidar, assembled in the truck for selective pollutant analysis - possessing spatial resolution of a few meters in the distance range extending from hundred of meters to a few kilometers. A reliable cascade mid-IR generation scheme was developed. Pulse energies up to milijoule in mid-IR have been already obtained using nonlinear AgGaSe<sub>2</sub> crystal. Optoacoustic and multipass cells were constructed for stationary spectrometers. Preliminary results with detection of CO<sub>2</sub>, CH<sub>4</sub>, H<sub>2</sub>O and other gases in the ppm concentration range show good sensitivity. Special pollutants were synthesized by chemical group of the project for spectrometric experiments: multiatomic nitrocompounds, such as trinitrotoluen (TNT) or trotyl, DNT (dinitrotoluoen), MNT (mononitrotoluoen) and RDX (heksahydro-1.3.5-triazyn). The mobile DIAL system based on the tunable laser in the 8-12 μm region, 10" goldmirror telescope, MCT cooled detector with control electronics is under construction and should be finished in 2005.
The cut-off effect in slightly asymmetric systems prevent the wider practical usage of long range surface polaritons (LRSP) in the infrared region. Due to asymmetry caused by the presence of even a few nanometers wide air gap the LRSP mode disappear. We propose a solution of this problem by using an effective medium approach. The basic idea is to compensate for the air gap induced asymmetry by introducing an additional layer into the system. That allows us to shift the cut-off to values sufficiently for experimental observation of LRSP. FTIR spectra of end-fire coupled LRSPs in the GaAs/Au/GaAs multilayer system were measured in the (800-3000) cm<SUP>-1</SUP> range. Various geometric and polarization sensitive effects of the infrared system capable of influencing the LRSP coupling is discussed. A pronounced increase in the p and s polarized light transmission ratio at long-wavelengths is explained as an increase in the propagation distance L of LRSPs. A fairly good fit between experimental and calculated curves was achieved at long wavelengths. The width of the air gap was used as a parameter in the calculations.
Optical and sorptive properties of cellulose have been investigated by three methods covering the wide 7000 - 80 cm<SUP>-1</SUP> spectral range. Attenuated total reflection spectra showed shift of sorbed water bands to shorter wavelengths under paper moisture increase. Surface electromagnetic waves (SEW) propagation at metal - Ge (film) - paper system were investigated firstly in far infrared region. Four slopes in the SEW intensity dependence versus time under paper drying were observed. Near infrared diffuse transmittance revealed a band of bonded to cellulose water at 1.53 micrometers which shows 0.08 micrometer red shift compared to 1.45 micrometer band of free water. Damping constants of cellulose sheets of various thickness were determined in the 140 - 85 cm<SUP>-1</SUP> range by the surface electromagnetic wave method. Sorptive properties of cellulose are compared to those of other sorbers made of divided silica.
In<SUB>2</SUB>O<SUB>3</SUB>(Sn) film CO senors in the Kretschmann configuration were investigated using a rotating analyzer spectrometer. From the experimental surface plasmon resonance (SPR) angular dependencies, applying the best fit method complex dielectric permitivity of In<SUB>2</SUB>O<SUB>3</SUB>(Sn) films ((epsilon) equals 2.4-i0.2) were obtained. Under exposition of sensor by CO gas at 134 degrees Celsius temperature, SPR shifted to higher angles and sufficiently broadened. Most significant change possesses an imaginary part of dielectric permitivity -- after 0.8% CO exposition it becomes 4.1, whereas a real part equals to 1.2.
Surface electromagnetic waves (SEW) due to their unique fielddistribution (field maximum occurs at the two adjacent mediainterface) is a highly sensitive instrument for studying both metalsurfaces and thin films on them. The experimentally measurableparameters in SEW experiments are the SEW propagation distance L(14=1/4m)nÃ¢â‚¬â€) and the real part of SEW refraction index n'ef efC C i/2i 2)). For metals in middle and far infrared region y,ef C +ci 2u01..) (p , - - plasmon frequency and damping constant) n' is directlyP p efdetermined by plasma frequency. Therefore, the difference between thelight line k =())/c and the surface polariton dispersion curve0k =w/chi is insignificant and in such circumstances the measurement$p efof n' is problematic. Usually it is measured by scanningefinterference pattern of bulk radiation with SEW launched on thesample edge . In the FIR region SEW propagation distance on metalsis too large (a few meters) and transparent films are sputtered on ametal surface with the purpose to press SEW field to the surface .For SEW phase spectroscopy in doped semiconductors additional is filmnot requires . Another method, proposed in , is based on SEWheterodyning and was realized on gold and copper at CO -laser2frequencies.
Experimental results of FIR ((nu) equals 85 - 142 cm<SUP>-1</SUP>) surface electromagnetic wave propagation in n-type semiconductors (InSb, GBaAs, InP) and ferroelectric films Ba<SUB>x</SUB>Sr<SUB>1-x</SUB>TiO<SUB>3</SUB> are presented. A technique for measuring the plasma frequency (nu) <SUB>p</SUB> and the damping constant of plasmons (gamma) (or the concentration and relaxation time of electrons) in doped semiconductors was designed. The SEW propagation distance dependence on electron concentration in GaAs has been obtained. The relationship between the SEW propagation distance L and the 'soft mode' parameters in ferroelectric films was found. In the L dependence on temperature the minimum was observed at T equals 380 K in Ba<SUB>x</SUB>Sr<SUB>1-x</SUB>TiO<SUB>3</SUB>, which is explained by the increase of dielectric losses tan (delta) in the film under phase transition.
The results of YBa2Cu3O7-x films on SrTiO3 investigation by far infrared surface electromagnetic waves (SEW) amplitude and phase spectroscopy at temperatures 80-350 K are presented. Strong SEW absorption at frequency 140 cm-1 has been observed. The origin of the observed absorption is proposed to be concerned with slab-phonons in YBa2Cu3O7-x. The optical constants of the films have been obtained. The complex SEW refraction index on temperature is explained, taking into account 'soft modes' features in SrTiO3 substrate. It has been determined that only the imaginary part of the SEW refraction index changes when the film transits into superconducting state, while the real part remains unchanged.
The investigation of thin film features on high reflectivity materials by optical methods is complicated due to small useful signal. Surface electromagnetic waves (SEW) is considered to be very perspective method for analysis of such materials. For SrTiO<sub>3</sub> SEW exist in FIR region (ν=88 - 807cm<sup>-1</sup>), except narrow gaps, and its propagation distance is about a few millimeters [1,2]. So, it can be easy measured. In the present paper we report the measurements of the optical features of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> films on SrTiO<sub>3</sub>(100) substrate by FIR SEW amplitude and phase spectroscopy at temperatures 80 - 300K.