Oscillator-amplifier Configuration Research Articles

Thermal lensing in copper vapor laser oscillator-amplifier configuration: Its measurement, role and compensation

A novel technique to measure the resultant focal length of the thermal lens in an amplifier using collimated beam of the oscillator for copper vapour laser system demonstrated. The resultant focal length was estimated using ray tracing approach in a 40 W system (CVL-40). Effect of input electrical power and neon buffer gas pressure on the resultant focal length was studied. Role of equivalent thermal lens in master oscillator power amplifier (MOPA) configuration was evaluated. Compensation techniques for minimization of the thermal lensing effect for a MOPA chain were theoretically studied using ray tracing in an equivalent lensing model. Compensation of thermal lensing for an eight module MOPA chain with CVL-40 (38 mm bore, 1.8 m long, 40 W, 9 kHz) systems studied. An eight-module MOPA chain configuration with minimized thermal lensing based on optimized compensation techniques is proposed. Our study finds benefits for high power laser systems used in various industrial, research and development applications like micromachining, high speed photography, bio-medical applications and pumping dye lasers for spectroscopy.

Analysis of the discharge plasma impedance of copper vapor laser

In the pursuit to analyze the impedance of copper vapor lasers (CVLs) in different conditions, a novel approach has been proposed in this paper. The underdamped behavior of the voltage waveform across the CVL is leveraged to compute the impedance of high-voltage discharge plasma in the laser. This methodology provides an accurate idea of the discharge plasma resistance and inductance as it is calculated on the basis of experimental voltage waveforms obtained from the laser system. The laser head inductance remains almost fixed and equivalent to ∼0.47 µH whereas the laser resistance changes between 34 Ω and 11 Ω depending on the discharge condition and its constituents. A critical evaluation of CVL impedance is done in all experimentally possible conditions, and a methodology has been proposed to maintain the CVL impedance, which results in the power stability of the laser in oscillator–amplifier configuration. The laser impedance variation w.r.t. time, pressure, operating voltage and electrode pin configuration has been investigated. The impact of the localized electric field at the electrode on the laser resistance has also been emphasized in this paper. A good concurrence exists between the calculated laser impedance and its experimental behavior.

Exploration of Jitter in Solid-State Switch-Based Pulse Power Supply of Copper Vapor Laser

The copper vapor laser (CVL) is the most powerful and efficient resonance metastable metal-vapor laser having widespread applications. Jitter requirements are very stringent when the CVL is operated in the oscillator–amplifier configuration. Jitter in the laser affects proper synchronization and thereby affects the output power and its stability. Although thyratron-based power supplies have low jitter, it has limited operational life. So, solid-state switch-based pulse power supply is preferable. In the solid-state switch-based pulse power supply of CVL, several parameters simultaneously contribute to jitter in the laser optical output. To observe the parameter-affecting jitter and its contribution, we carry out MATLAB simulations, which are experimentally validated. We demonstrate by simulation and experiments that variations in the laser load impedance significantly contribute to jitter and, by minimizing the effect of laser load variations on the power supply, jitter in the laser can be significantly reduced.

Effect of addition of H2 to the He buffer gas on amplifying parameters and output power of a copper bromide laser

A pair of copper bromide lasers in an oscillator–amplifier configuration was used to investigate the effect of the addition of hydrogen to the helium buffer gas on the small-signal gain (g0), saturation energy intensity (Es) and output power (Pout) of the laser. The addition of a small amount of hydrogen to the He buffer gas in a CuBr laser caused approximately doubling of the amplifying parameters and average output power of the amplifier. The amplifying parameters and output power of the system were measured at different input electrical powers of the amplifier, and optimum input powers of 1.75 and 1.65 kW were obtained for He and He–H2 gases, respectively. The maximum g0, Es and Pout achieved are 0.068, 0.090 ; 47.6, 77.1 and 9.8, 20.9 W, respectively, using He and the He–H2 admixture. It was concluded that using He with H2 was more efficient and produced higher output power than using pure He in the CuBr lasers.

Soft x-ray laser beamline for surface processing and damage studies.

We have developed a soft x-ray laser (SXRL) beamline equipped with an intensity monitor dedicated to ablation study such as surface processing and damage formation. The SXRL beam having a wavelength of 13.9 nm, pulse width of 7 ps, and pulse energy of around 200 nJ is generated from Ag plasma mediums using an oscillator-amplifier configuration. The SXRL beam is focused onto the sample surface by the Mo/Si multilayer coated spherical mirror. To get the correct irradiation energy/fluence, an intensity monitor composed of a Mo/Si multilayer beam splitter and an x-ray charge-coupled device camera has been installed in the beamline. The Mo/Si multilayer beam splitter has a large polarization dependence in the reflectivity around the incident angle of 45°. However, by evaluating the relationship between reflectivity and transmittance of the beam splitter appropriately, the irradiation energy onto the sample surface can be derived from the energy acquired by the intensity monitor. This SXRL beamline is available to not only the ablation phenomena but also the performance evaluation of soft x-ray optics and resists.

Various buffer gas effects on amplifying parameters of a copper bromide laser

A pair of Copper Bromide lasers in an oscillator–amplifier configuration was used to study the dependence of the small-signal gain (g0), saturation energy intensity (Es) and output power on various types of Buffer gases in CuBr vapor lasers. The amplifying parameters and output power of the system were measured at different buffer gas pressure and the optimum pressure of 11, 17 and 23 torr were obtained for He, He–Ne and Ne, respectively. The values of these parameters were different for various gases used in the gain medium. It was shown that the use of He has more efficient and output power than that of Ne or their mixed ones in CuBr lasers. The type of buffer gas used in the gain medium can affect the microscopic parameters, which in turn affects the operation and output power.

Amplifying characteristics of small-bore copper bromide lasers

A pair of copper bromide lasers in an oscillator–amplifier configuration was operated to measure and compare the small-signal gains and saturation intensities, as amplifying parameters of different laser tube lengths. The independencies of these amplifying parameters on the different amplifier tubes length with identical diameter were investigated, individually. Therefore, the output powers of the system were measured in different tubes lengths of amplifier and the optimum conditions were obtained. It was shown that, by changing the amplifier tube length, the amplifying parameters remain nearly constant without any remarkably changing, but the output power of the system was increased linearly due to increase of tube length. The experimental results were in good agreement with the theory. Moreover, the radial gain distribution was studied.

Frequency dependence of the amplifying parameters of a CuBr laser

A pair of copper bromide lasers in an oscillator–amplifier configuration was used to investigate the small-signal gain and saturation intensity as amplifying parameters in terms of pulse repetition frequency. Some fluctuations in the laser output power were recorded by varying the excitation frequency from 13 to 29 kHz as well as the amplifying parameters. The effect arises from the laser tube, which performs as both an optical resonator and an acoustic resonator. At some frequencies, which were matched by tube acoustic resonance, the acoustic energy overcomes the optical energy. The relation between frequencies that give maximum and minimum laser output powers was obtained so that the frequency that corresponds to a minimum laser output power is the average of two adjacent frequencies that correspond to a maximum output power. An empirical formula was obtained to calculate the optimum operational frequency in terms of tube diameter, which gives a maximum laser output power. The efficiency of the laser is highest at the lowest pulse repetition frequency, which gives considerable output power.A pair of copper bromide lasers in an oscillator–amplifier configuration was used to investigate the small-signal gain and saturation intensity as amplifying parameters in terms of pulse repetition frequency. Some fluctuations in the laser output power were recorded by varying the excitation frequency from 13 to 29 kHz as well as the amplifying parameters. The effect arises from the laser tube, which performs as both an optical resonator and an acoustic resonator. At some frequencies, which were matched by tube acoustic resonance, the acoustic energy overcomes the optical energy. The relation between frequencies that give maximum and minimum laser output powers was obtained so that the frequency that corresponds to a minimum laser output power is the average of two adjacent frequencies that correspond to a maximum output power. An empirical formula was obtained to calculate the optimum operational frequency in terms of tube diameter, which gives a maximum laser output power. The efficiency of the laser is...

Synchronization effect on the small-signal gain and saturation intensity of a CuBr laser

A pair of copper bromide laser in an oscillator–amplifier configuration was used to investigate the small signal gain and saturation intensity as amplifying parameters, versus delay time of triggering between lasers. The maximum amplifying parameters and output power of 0.07 cm−1, 43 μJ cm−2, and 9 W were measured, respectively at optimum delay time of about 10 ns. The amplifying parameters and measured output power of laser versus delay times between intervals of 6–43 ns, shows some local maxima and minima. The output power extracted from the amplifier exceeds that achieved with the same device as the oscillator by more than 60%.

Pressure Dependence of the Small-Signal Gain and Saturation Intensity of a Copper Bromide Laser

A pair of copper bromide lasers in an oscillator–amplifier configuration is used to investigate the small signal gain and saturation intensity as amplifying parameters and output power of lasers, versus pressure of buffer gas. It is shown that the amplifying parameters and laser output power have a maximum value at optimum buffer gas pressure of 11 Torr. The challenge between microscopic parameters such as stimulated emission cross section, laser upper level lifetime, and population inversion, which determine the values of laser characteristics respective to the operational pressure of buffer gas, are investigated. Thus an optimum delay time of about 10 ns is determined, and a maximum output power equivalent to about 12 W is extracted. The amplifying parameters and measured output power of laser versus delay times show some local maxima and minima at the delay time interval of 6–43 ns.

The behavior of gain and saturation characteristics versus temperature in a copper bromide laser

A pair of copper bromide lasers in an oscillator–amplifier configuration was used to investigate the temperature dependence of the small-signal gain, saturation intensity, and output power of the laser. The observations were explained in terms of the electron temperature and energy levels of transition. An optimum electrical input power of 1.6 kW and a corresponding operational temperature of 510 °C were determined for the maximum values of these parameters. The balance between the microscopic parameters, such as stimulated emission cross-section, laser upper-level lifetime, and population inversion, which determine the behavior of the amplifying parameters and laser output power with respect to the operational temperature, has been investigated. We used the steady-state rate equation from the Hargrove model to determine the amplifying parameters, instead of the Frantz–Nodvik formula. The power extracted from the amplifier exceeds that achieved with the same device as the oscillator by more than 60%.

Analysis of the soft X-ray laser oscillator-amplifier configuration based on self-filtering unstable resonator

In this paper, the oscillator-amplifier (osc-amp) configuration based on self-filtering unstable resonator (SFUR) as oscillator has been proposed and theoretically analyzed for soft X-ray lasers. The configuration is suitable for soft X-ray lasers because their active medium has a short-gain-lifetime. The nearly gaussian profile and low beam divergence of SFUR makes it superior than the amplified spontaneous emission mode soft X-ray lasers. However, osc-amp is proposed to compensate the low output energy of SFUR and preserves the high beam quality and coherency. Our calculations indicate that the increasing of laser energy by a factor of 100 is possible with a single stage amplifier where leads to a high beam quality micro-joules soft X-ray laser.

Impact of cavity loss on the performance of a single-mode Yb:silica MOFPA array

In this work, the numerical analysis of an end-pumped continuous-wave (CW) double-clad (DC) master oscillator fiber power amplifier (MOFPA) configuration with linear-cavity has been carried out, based on the set of propagation rate equations. The modified analysis considers the distributed losses of pump coupling, fiber end-face cleaving (air-reflection), splice points, combiners, fiber Bragg gratings (FBGs) as well as scattering losses and parasitic noises due to amplified spontaneous emission (ASE) along the array. Furthermore, a series of experiments have been performed using a home-made oscillator–amplifier configuration. The empirical data taken from the single-mode (SM) ytterbium (Yb)-doped silica fiber laser amplifier were used to verify the numerical simulation accordingly. • The modified simulation for home-made lossy Yb:silica MOFPA array is presented. • Rate equations are developed by considering the loss of each passive component. • Parasitic ASE noise is investigated for fiber amplifier in small-signal regime. • The simulation is validated using data taken by systematic experiments.

Dependence of the amplifying parameters on buffer gases in copper-vapor lasers

We use a pair of copper-vapor lasers in the oscillator–amplifier configuration for investigating the small-signal gain and the intensity saturation as the amplifying parameters, versus the pressure of various types of buffer gases. We show that the small-signal gain increases and the intensity saturation decreases with increase in the air pressure. Moreover, the values of these parameters are different for various gases used in the amplifier media. We show that both parameters are greater at the atmosphere of neon as a buffer gas than that of a mixture of helium and neon or air.

Frequency dependence of amplifying parameters of a copper vapor laser using air as a buffer gas

We use a pair of copper vapor lasers in an oscillator–amplifier configuration to investigate amplifying parameters such as the small signal gain and the saturation intensity versus the pulse repetition frequency when two different types of buffer gases are employed. We show that the values of these parameters are not the same if different gas mixtures are used in the gain medium. We show that the values of the parameters are estimated to be higher if a He–Ne buffer gas is used than in the case of air. The laser output power is relatively high and has fairly good stability at some special pulse repetition frequencies when air is used as a buffer gas.

High pulse energy output from tunable solid-state dye laser based on MPMMA doped with PM567

Tunable solid-state dye laser sample based on modified polymethyl methacrylate (MPMMA) with methanol co-doped with pyrromethene 567 (PM567) and Coumarin 440 (C440) was prepared. Tunable dye laser output wavelength from 546 to 594 nm was obtained in an oscillator-amplifier configuration. With the input seed laser energy being about 1.5 mJ, the highest dye laser output energy reached 113.9 mJ, and the corresponding conversion slope efficiency was 51.39%. To the best of our knowledge, the tuning range and narrow linewidth dye output energy is the best under the same condition so far. The linewidth for the seed laser and amplified laser were measured with the result of less than 0.2 nm. With the amplified medium being pumped at a repetition rate of 10 Hz with a pulse energy as high as 120 mJ (the fluence was 0.42 J/cm2), the laser output energy dropped to half of its initial value after approximate 43000 pulses.

Small-signal gain dependence on active medium length and axial thermal profile in metal-vapor lasers

We measure the small-signal gain coefficient g0 of a gold vapor laser for a 627.8 nm transition through the implementation of a discharge-driven oscillator-amplifier configuration. We study the gain dependence on the length of the laser active medium. In addition, we measure the output power of a copper-vapor laser for two different thermal insulator distributions and simulate the thermal-length profile to determine the effective length of the active medium. We show that the small-signal gain coefficient depends on the effective length of the active medium and do not depend on the physical (actual) length of the active medium.

On the operation of switch-less transversely excited atmosphere CO2 lasers in the oscillator and amplifier configurations

The work presented in this paper deals with the triggering aspect of a switchless laser. Many methods were utilized to affect the operation of two switch-less lasers in the oscillator-amplifier configuration. Most satisfactory performance in terms of the range and reliability of the delay was obtained with the LC inversion-based triggering option.

Pressure dependence of small signal gain and saturation intensity of a gold-vapor laser using various buffer gases in gain medium

A pair of gold-vapor laser (627.8 nm) in an oscillator–amplifier configuration was used to investigate the small signal gain, g 0, and saturation intensity, I s, as amplifying parameters, versus pressure at various types of buffer gas. It was shown that the small signal gain decreases and saturation intensity increases linearly with increasing the pressure. Moreover, the values of these parameters are different using various gas mixtures in gain medium. Both parameters were estimated to be more at helium buffer gas atmosphere than that of neon or their mixed ones.

Demonstration of a highly coherent 13.9 nm x-ray laser from a silver tape target

A highly coherent 13.9 nm x-ray laser (XRL) is generated under an oscillator-amplifier configuration using a new tape target system and a driver laser system with a 0.1 Hz repetition rate. The output energy is comparable to the XRL generated with a silver-deposited slab target, and the pointing stability using the new tape target system is better than conventional slab targets.