We present a simple and cost-effective method for the fabrication of optical elements in the terahertz regime. Caramelized sucrose is used as the refractive medium in the frequency range from 0.1 to 0.4 THz. The absorption coefficient of 7 cm−1 and the high index of refraction of 2.45 at 0.3 THz enables the fabrication of thin optical elements in the near-millimeter wavelength range. The THz beam profiles of the fabricated parabolic lens in focus, evaluated with terahertz pulsed imaging, show the near diffraction limit performance.
In this paper we report a new approach to linking the terahertz spectral shapes of drug candidates having a similar molecular structure to their chemical and physical parameters. We examined 27 newly-synthesized derivatives of a well-known nonsteroidal anti-inflammatory drug Piroxicam used for treatment of inflammatory arthritis and chemoprevention of colon cancer. The testing was carried out by means of terahertz pulsed spectroscopy (TPS). Using chemometric techniques we evaluated their spectral similarity in the terahertz range and attempted to link the position on the principal component analysis (PCA) score map to the similarity of molecular descriptors. A simplified spectral model preserved 75% and 85.1% of the variance in 2 and 3 dimensions respectively, compared to the input 1137. We have found that in 85% of the investigated samples a similarity of the physical and chemical parameters corresponds to a similarity in the terahertz spectra. The effects of data preprocessing on the generated maps are also discussed. The technique presented can support the choice of the most promising drug candidates for clinical trials in pharmacological research.
The experiment is performed on a three-mirror laser resonator. The injection is arranged in two ways: by a feedback from the movable third mirror, and by chopping the running back laser beam when the third mirror is stable.
The paper describes the results of investigations of optical phenomena on an RF excited slab-waveguide CO2 laser. The
experiments are performed in two optical arrangements: two-mirror resonator and three-mirror one. The main purpose of
the experiments is to check possibilities to observe the optical phenomena using a microphone. The laser plasma is
modulated with a self-mixing signal in the three-mirror resonator. The response of the microphone is observed and
analyzed. Detection of the laser signature phenomenon with the microphone is experimentally considered. The
experiments are done at cw regime of the laser. The investigations are performed at pulse operation of the laser, as well.
The response of the microphone is analyzed. It is checked how the laser pulse is reconstructed at a profile of the
microphone signal. The output laser pulse with a mapped laser signature in the laser pulse profile is compared to the
microphone signal shape. The presence of the laser signature at the acoustic signal is investigated.
The paper gives an algorithm for elaboration of the RF excited slab-waveguide CO2 laser working on one chosen emission line in a pulse regime. The solution of the problem bases on an RF transversal excitation in a slab-waveguide laser structure and laser signature phenomenon. The structure gives a homogeneous distribution of the excited laser plasma along the electrodes. The plasma in the structure is stable and reproducible from the pulse to pulse comparing to conventional tube lasers, and particularly to flow dynamic lasers. On the other hand, the applied unstable kind optical resonator produces a single-mode operation by definition. It suppresses higher modes in the laser cavity. The only problem are parasitic "hooting modes" created along the waveguide direction - between electrodes. But usually they do not bring too much perturbations to a spectral contents of the laser output radiation. The problem of the one-color operation of the laser can be solved by careful selection of the laser signature. The paper shows the results of the experiments, and gives the methodology to design the CO2 laser in a pulse regime operating on one chosen emission line. Controlled two-color and multi-color pulsed operations are also considered. The results can be applied to design lasers for the trace gas analysis around of 10 or 9 μm or other spectral devices. It can be also applied for material processing of the media sensitive for the wavelength of the laser radiation.
Results of the investigations on an RF pulsed excited CO2 laser plasma are given in the paper. A slab-waveguide configuration of the laser is used. An unstable positive branch resonator structure is applied to ensure a single-mode operation of the laser. The configuration of the laser system guaranties a spectral purity of the laser output radiation, and makes the investigations clear. As known, a pulse excitation introduces dramatic perturbations of the laser plasma pressure, and temperature. The density of the laser gas mixture, or in other words, the refractive index is changed during the input pulse developing, as a consequence. The laser radiation frequency is changed in time of the laser pulse duration. Sometimes it is a parasitic effect, when a single-frequency laser operation is required. The aim of the work is to give a clear picture of the laser plasma behavior caused by a pulse excitation of the laser medium. The results obtained gives a possibility to elaborate the method of a laser frequency control in a pulsed regime.
The paper presents studies on influence of the gas laser cavity shape on an acoustic wave created in the cavity. Results of investigations on an RF excited CO2 slab-waveguide laser are shown. As is demonstrated, rapid changes of a laser plasma pressure appear in the laser gas mixture as a consequence of the pulsed RF discharge in the laser. The pressure variations create an acoustic wave propagated in the laser chamber, and involve changes of the refractive index of an excited plasma. As a result, the frequency of the optical wave emitted by the laser changes - a "line hoppings" effect appears. In the case of the slab-waveguide laser an acoustic wave propagates in a closed space - the laser reservoir, that is a special kind of an acoustic resonator. As known, a material from which cavity is made, a shape of the walls and their mutual position are significant for a wave propagation. In the experiment, the walls of the chamber are made of aluminum, so it is a very reflecting area. More, the walls are parallel that is an advantageous condition for creating standing waves. The aluminum wedges were used in the experiment to change the geometry of the reservoir. The influence of pulse duration time on the acoustic signal is investigated.
A servomechanism for identification of the CO2 laser lines, and searching desired laser signatures is elaborated. The laser signature is used as a standard for calibration of the servomechanism. Algorithms for process automation are find. The system can be used in servo-loop mechanisms for stabilization of the laser operation to a chosen emission line. The method can be expanded using different isotopes of carbon, and/or oxygen molecules in the laser medium. Some applications of the method are suggested.
Thermodynamic and optical parameters of the CO2 slab-waveguide pulsed laser are given. The methodology of the investigations is based on a known Gladstone-Dale formula, linking the refractive index of the fluid, density (or pressure), and temperature of the medium.
An acoustic wave changes, by definition, the pressure of the gas medium. The power delivered to the pulsed gas laser changes the pressure (and temperature) of the laser medium. The monitoring of the acoustic wave in the laser cavity, taken as a specific acoustic resonator, can be an easy measure of the local changes of the laser gas pressure. The changes of the pressure involve changes of the laser gas density, and changes of the refractive index, as a consequence. It leads to a frequency tuning of the laser optical resonator. In the case of the CO2 laser a rotational line hopping phenomenon is observed as a result. In other words, a single frequency operation of the RF excited CO2 laser with a pulsed plasma is problematic. The main goal of the experiment is to give a picture of the laser plasma behavior during the pulsed excitation of the CO2 laser medium.
A pulsed excitation of the laser plasma in gas lasers creates an acoustic wave in the laser reservoir. It changes thermodynamic parameters of the laser plasma in the laser cavity like pressure, and temperature, as well, and consequently it changes the density of the laser plasma, or, in other words, the refractive index of the laser medium. Tuning laser frequency during the pulse developing is observed as a result. The measurements of the pressure, temperature, and refractive index changes in an RF pulsed excited CO2 slab-waveguide laser are purposes of the work. The pressure changes are measured with calibrated microphones situated close to the laser plasma. The temperature changes are calculated via measured refractive index characteristics, and simple formulas linking the refractive index with the gas density. The picture of the acoustic wave propagation in the laser cavity is presented. The obtained results give the picture of the laser plasma behavior during the pulsed excitation. It leads to a single frequency pulsed laser operation design.
It has been shown, that a single line operation of the CO2 laser can be easier sustained by careful choosing the laser resonator length. Selection of the right resonator length allows obtaining very sophisticated signatures.
The paper is an attempt at reconstructing the academic life in Wroclaw (Breslau) before the Second World War. Included are fourteen Nobel Prize Winners whose life was connected in different way with the city. The scientists are divided into three groups - born in Wroclaw (Breslau), studying in the city, and working at the Wroclaw (Breslau) University.
Results of the investigations of pulsed CO2 laser plasma are presented. Theoretical calculations of temperature and pressure changes and their influence on laser tuning during the pulse evolution have been experimentally proven. The laser slab-waveguide structure equipped with an unstable resonator has been used in the experiment.
The qualitative and quantitative description of the laser tuning effect during a pulse forming has been described. The mechanism of the line hopping in the CO laser has been presented. A simple arrangement enabled observing the pulse evolution of all oscillating spectral transitions contributing in the total shape of the output pulse. As shown in the experiment, the jumps from line to line over the pulse duration give the sequence of lines, which is the subsequence of the static laser signature. Thus, the changes of the refractive index can be estimated by setting the static signature against the line hopping during the pulse operation of the laser. On the other hand, the changes of the refractive index during the pulse evolution have been measured directly with a Mach-Zehnder interferometer. The experiment has been performed on the slab-waveguide laser with an unstable positive branch optical resonator. The experiment allowed observing the dynamic evolution of the pulse in time and spectrum. The method of the investigations allows estimating the changes of a pressure and temperature during the pulse evolution, and can explain the effect of bulges observed at the output pulse shape.
The overview of spectral properties of the CO2 laser radiation in modern RF excited waveguide, multi-waveguide, and slab-waveguide laser structures is given. Spectral phenomena in lasers operated in a pulse regime are also demonstrated. The influence of specific spectral features of the CO2 laser on designing the high-brightness and spectrally pure laser devices is shown.
Each mode inside a rectangular slab-waveguide laser consists of four quasi plane waves propagating at small angles to its axis and inducing specific grating ofthe refractive index in the slab medium. Multimode operation of such laser is a superposition of single modes. Each mode can be spatially separated into two high quality lobes with M2 parameter near l . When geometry ofthe slab is controlled, high stability of a mode pattern can be obtained. This effect is particularly strong when extra single mode selection (for example Talbot filtering) is applied. The experimental evidences were performed on a RF excited CO2 slab-waveguide laser.
Results of investigations of RF excited CO2 waveguide lasers in pulse regime are described. The shapes of the output pulses monitored and simulated for the different operation conditions are shown. The characteristics of the power levels are presented. Some aspects of spectral properties of the laser output radiation in pulse regime are given.
Spectral aspects of pulse operation of RF excited CO2 waveguide lasers are presented. The hopping of emission lines were monitored and identified through the pulse duration of the laser. Syntheses of the laser total output pulse shapes were done summing of all lines taking part in oscillations.
RF excited plasma in a molecular slab laser modifies an impedance of the laser head. We present a simple and practical procedure to correct a laser head impedance changed due to a sheaths capacity. Experimental results for a CO2 laser are given.
Different aspects of pulse operation of RF excited CO2 waveguide lasers are presented. The shapes of the output pulses were monitored for the different operation conditions. Peak power, average power and delay time of pulses were measured.
We present the way of forming Bragg gratings in so-called slab lasers. Four running waves in the space of a slab optical resonator create an induced diffraction grating like acousto-optical or holographic gratings. The experimental evidences were performed on a RF excited CO2 slab- waveguide laser.
The new generation of slab waveguide molecular lasers requires new resonators ensuring high extraction of output powers and high beam quality. In this paper we describe a few configuration of laser resonators which seem to be quite attractive for these requirements.
The construction of 875 mm long transversally rf excited carbon-dioxide waveguide laser is presented. We show the results of the laser operating in single EH11 waveguide mode for the rectangular aperture of the laser channel equal to 1.7 multiplied by 4 mm.