A. Ioannou

The influence of the external circuit on arc-discharge of a spark-gap: its application to a pulsed gas laser

An investigation of the influence of the driving circuit on the arc-discharge of a spark-gap takes place in this work. The two most common types of circuits used in pulsed gas lasers have been studied for all possible combinations of capacitance allocation. In these circuits the spark-gap is used as ignition system and participates in the electric circuit through its resistance and inductance. This consideration shows that capacitances act as charge containers and feed the arc-discharge in the spark-gap independently of their positions in the circuit. Their values influence the total charge contained in the arc discharge and this, in its turn, influences the discharge resistance. On the other hand, total charge flows through the discharge at a rate determined by the coupling of the circuit loops, namely, by the circuit type. Thus, circuit type influences the drift velocity and this, in its turn, influences the channel radius, which determines the discharge inductance. >

Study of electro-optic effects in organic chromophores by use of a waveguide geometry

The linear electro-optic coefficients r33 and r13 of a highly nonlinear organic chromophore were measured via an experimental method based on waveguide sample geometry. The technique used is simple and accurate and the interpretation is straightforward. Viscous solution of chromophore and PMMA were prepared in chlorophorm (CHCl3) and films were made by drop casting of these solutions onto metallic substrates. A DC poling electric field Vp was applied, in order to polarize the doped molecules and a linearly polarized beam from a He-Ne laser was left to pass through the film. A polarizer placed in front of a photodiode was used to determine the polarization state of the beam, allowing us to measure the magnitude of the induced birefringence Δn. The electro-optic coefficients difference (Δn=r33-r13) was calculated via the induced birefringence. The dependence of the coefficients r33 and r13 on the concentration of chromophore in PMMA was also investigated. By applying an AC electric field onto the film the dynamic electro-optic effects can be studied.

Electrical characteristics of the discharge in a pulsed gas laser

The resistance and inductance of a laser discharge in a pulsed gas laser are considered theoretically in this paper. The total charge and the dimensions of the discharge volume are responsible for the resistance and inductance of the laser channel respectively. Generally, the inductance increases either decreasing electrode length or discharge thickness, or increasing the interelectrode distance. The direct dependence of the resistance and inductance with the microscopically plasma parameters, total charge and drift velocity, was discovered in this paper through the external driving circuit and especially through its capacitance. The values of the capacitors form the total charge while the coupling of the capacitors in the circuits forms the drift velocity. These are inferred dealing with the two most common circuits used in a pulsed gas laser, namely the doubling circuit and the charge transfer circuit for all possible combinations of capacitance allocation.

Time dependent resistance and inductance of the laser discharge in a pulsed gas laser through waveforms of the voltage and current

A new method of finding the time histories of the resistance and inductance of a discharge in the laser chamber of a pulsed gas laser is described. This method exploits simultaneously the voltage across the laser channel and the flowing current in the laser discharge while the knowledge of the entire circuit is not required. The mathematical model used is simple and the results show strong variations of the resistance and inductance during the formation phase of the discharge while in the main phase these quantities fluctuate around constant values.

The electric behavior of a capacity-transfer-type pulsed gas laser

In the present work the electric behavior of a Capacity-Transfer-Type N2 laser has been studied in relation to storage and peaking capacitors. The results showed that the resistance and inductance of discharges in the ignition system and in the laser chamber vary as the values of the capacitors change. This occurs because the driving circuit, and particularly its capacitances, affect the formation of the two discharges and finally the laser output. The coupling of the two circuit loops is weak and is achieved through laser channel inductance. Finally, the behavior of the laser output versus storage and peaking capacitors is determined from a) the electric energy deposited in the laser channel, as a short pumping pulse and b) the laser oscillation time delay which depends on the upper laser level and the Q factor of the cavity.

Determination of the electrical characteristics of the discharges in a pulsed gas laser through its current waveforms

A method of finding the time dependent resistance and inductance of the discharges in the switch system and laser chamber in pulsed gas lasers is described in the present work. According to this method the current waveform is digitized and the first and second derivative is calculated through a computer. For a certain time instant, substituting the value of the current and its first and second derivative into the integrodifferential equations describing the performance of the circuit loops, we form relationships which connect the values of the resistance and inductance for this particular time instant. Combining relationships originated from very closed adjacent time instants, the values of the resistance and inductance can be found. Scanning the entire time region of the discharge, the time history of the resistances and inductances of the discharges are revealed. Their behavior shows for the resistances an abrupt drop while for the inductances a sharp peak, both during the formation phase. After that the above characteristic quantities fluctuate slowly around constant values.

Method of measuring currents in pulsed gas lasers

The comprehension of the performance of pulsed gas lasers requires knowledge of several parameters which are time dependent and consequently difficult to measure. These parameters are mainly influenced by the two electric discharges which take place during the laser performance, namely by the ignition system and laser tube. The present work illustrates a new method to determine the most fundamental of these parameters, the current. This can be achieved exploiting only the voltage waveform on which much concealed information exists about all the time dependent parameters. The revelation of these parameters can be achieved by further elaboration of the waveforms of the high voltages. This elaboration, in our case, leads to finding the current and is described in this paper. The method is applied to a simple RLC circuit, to a doubling, and to a C-to-C circuit and it is delivered from experimental errors existing in other methods achieving the best accuracy to date.