High-pressure CO2 Laser Research Articles

Generation of tail-free short pulses using high-pressure CO2 laser

The spectral linewidth of a transversely excited pulsed CO2 laser is broadened at high working pressures. This phenomenon causes a decrease in the upper-level lifetime such that the pulse width is significantly compressed. Although the tail part of CO2 laser pulses owns a non-negligible proportion of total energy, it has minor effects during the interaction process between photons and materials due to its low amplitude. Thus, it is of great significance to yield the tail part and generate a narrow pulse in most applications. In this study, a continuously tunable pulsed CO2 laser with a low nitrogen proportion in the mixture is developed to generate tail-free short pulses; a minimum pulse width of 30.60 ns with a maximum pulse energy of 481 mJ is synchronously achieved at a pressure of 7 atm, and the estimated peak power is above 15 MW. A numerical simulation is also conducted for comparison with the experimental results. The contribution of the spectral gain toward the compression of the pulse width is discussed in the last section of this paper.

Two-color emission of BaWO4 crystals pumped by 472 nm 0.11 ps laser pulses for frequency conversion into the longwave IR domain

The frequency conversion of Ti:Sapphire laser second harmonic pulses into two-color emission using a tandem of BaWO4 Raman crystals was experimentally demonstrated with an internal efficiency of ∼17%. The output emission contained symmetrical Stokes and anti-Stokes spectral components separated by 902 cm−1 with a full-width half-maximum bandwidth of ≥110 cm−1 each. The applicability of this two-color emission was numerically verified for the production of longwave infrared ultrashort pulses suitable for seeding a high-pressure CO2 laser amplifier via difference frequency generation in LiGaS2 crystal.

Demonstration of a 2 ps, 5 TW peak power, long-wave infrared laser based on chirped-pulse amplification with mixed-isotope CO2 amplifiers

We report generation of 5 TW peak power in a 2 ps pulse at 9.2 µm via chirped-pulse amplification (CPA) in mixed-isotope high-pressure CO2 laser amplifiers. This represents the highest peak power in a single picosecond pulse format and the shortest pulse at terawatt peak power ever achieved in the long-wave infrared (LWIR) spectral range. Maximum demonstrated energy of the compressed pulse is 14 J and minimum period between shots is 20 s. The successful implementation of the chirped pulse amplification technique in a short-pulse gas laser opens a route to development of LWIR laser facilities with tens of terawatts of peak power, thus approaching the number of photons per optical cycle of current near-infrared laser systems based on solid-state active media.

Theoretical investigation of the regenerative amplification of ultrashort pulses in a high-pressure transverse electric CO2 laser.

We have developed a theoretical model for the regenerative amplification of ultrashort mid-infrared radiation in high-pressure transverse electric discharge CO2 lasers. This model is based on counter-propagating wave equations that are combined with Boltzmann equation, six-temperature, and circuit-coupled kinetic models. For the first time to our knowledge, the effect of spontaneous emission is taken into account. The model describes noise behavior, contrast ratio, and self-lasing of amplified spontaneous emission. The proposed scheme allows the attainment of a few-picosecond pulse with GW-level peak power and contrast ratio on the order of 106 in the 9μm range.

Direct acceleration of electrons by a CO2 laser in a curved plasma waveguide.

Laser plasma interaction with micro-engineered targets at relativistic intensities has been greatly promoted by recent progress in the high contrast lasers and the manufacture of advanced micro- and nano-structures. This opens new possibilities for the physics of laser-matter interaction. Here we propose a novel approach that leverages the advantages of high-pressure CO2 laser, laser-waveguide interaction, as well as micro-engineered plasma structure to accelerate electrons to peak energy greater than 1 GeV with narrow slice energy spread (~1%) and high overall efficiency. The acceleration gradient is 26 GV/m for a 1.3 TW CO2 laser system. The micro-bunching of a long electron beam leads to the generation of a chain of ultrashort electron bunches with the duration roughly equal to half-laser-cycle. These results open a way for developing a compact and economic electron source for diverse applications.

Carbon dioxide laser with an e-beam-initiated discharge produced in the working gas mixture at a pressure up to 5 atm

A high-pressure CO2 laser with a discharge initiated by an electron beam of sub-nanosecond duration in the laser gas mixture at a pressure up to 5 atm is fabricated. For the 20-ns pulses the energy from the active volume ∼ 4 cm3 amounted to 40 mJ. The laser operation at a pulse repetition rate up to 5 Hz is demonstrated. In the gas mixture CO2:N2:He = 1:1:6 at a pressure 5 atm, the specific energy deposition of ∼ 0.07 J cm-3 atm-1 is obtained in the process of a non-self-sustained discharge with ionisation amplification.

Modulation of corticofugal receptive field induced by synaptic plasticity in bat auditory system

The visible luminescence of ethylene in a focused 109W/cm2 continously frequency-tuned field of a high-pressure CO2 laser was investigated. Q-branch excitation resonance was observed width of 10 cm-1. No direct correlation between detailed rotational structure and intensity of luminescence was revealed.

High-power, high-pressure pulsed CO2 lasers and their applications

The paper is devoted to problems associated with the construction of high-power pulsed CO2 lasers and high-pressure amplifiers and to an analysis of the possible ways of their solution. Prospects of the development of such lasers and their applications in technological processes are considered. Original designs of a laser complex for obtaining the carbon-13 isotope and a superatmospheric-pressure CO2 amplifier are presented.

Photoacoustic gas sensing employing fundamental and frequency-doubled radiation of a continuously tunable high-pressure CO 2 laser

We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed. The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated with measurements on NO and CO2. The measured isotope ratio 15NO/14NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.

High-pressure pulsed CO2 lasers

This paper presents a large body of data allowing one to determine the energy, time, and spectral characteristics of high-pressure pulsed CO2 lasers over wide ranges of parameters.

High-power high-pressure pulsed CO2 lasers

The results of investigations and development of high-pressureCO 2 lasers are considered. It is shown that the high-pressure active medium allows radiation pulses to be formed with smooth tuning of frequency and duration over wide ranges. Data on small-size wide-apertureCO 2 lasers with an output pulse energy up to 5 kJ are presented.

New FIR Emissions in Ammonia by Pumping with a Line Narrowed High Pressure CO2 Laser

In this work we report several emissions observed in Ammonia in the 25-400 μm range by pumping with a line-narrowed CO2 laser. Several new lines are observed mainly due to the increased pump resolution that allowed us to detect weaker lines adjacent to stronger ones and also to reduce the threshold power.

Wideband Tuning of a High-Pressure CO2 Laser by means of Intracavity Active Frequency Shift

Intracavity active frequency shift, a unique method of shifting the frequency of pulsed lasers, was applied to a high-pressure CO2 laser which has a continuous gain profile over a wide range of the spectrum. In order to extend the amount of frequency shift, the dependence of the maximum frequency shift on the laser gas pressure was investigated. As a result, it was found that the maximum frequency shift was limited by the gain duration time rather than by the gain bandwidth at a pressure of 8–10 atm. By shortening the cavity length, the maximum frequency shift of 9 GHz was obtained at a pressure of 8 atm. Then, the grating-mirror cavity was applied to demonstrate the frequency shift starting from each lasing line of the CO2 laser. According to numerical calculations, the maximum frequency shifts starting from most lasing lines of a multi-isotope cw CO2 laser can exceed 10 GHz, resulting in coverage of almost the entire gain spectrum in the high-pressure CO2 laser.

Generation of tunable far-infrared radiation by optical pumping molecular gas lasers

This paper summarizes the results obtained by optical pumping molecular gas lasers by use of a 20 atm high-pressure CO 2-laser. The far-infrared laser gases investigated were several isotopes of the methylhalides (CH 3X; X  F, Cl, Br, I), heavy water (D 2O) and ammonia (NH 3), that delivered around 1000 laser lines with wavelengths ranging from the millimeter region down to 40 μm. By exploiting the continuous tunability of the CO 2-laser to pump either a waveguide laser or a multipass Raman-cell broadly tunable FIR emission can be generated via stimulated Raman scattering. Moreover the observed far-infrared laser pulses were found to have pulse durations of less than 100 ps.

Spectral Fluctuations in the Stokes Output Pulse Pumped with a High-Pressure CO2 Laser

Analytical solution of the broadband Stokes field, whose linewidth is 2 GHz full width at half-maximum (FWHM), in four-wave mixing based upon stimulated Raman scattering is obtained using the fully quantum mechanical approach developed by Raymer et al. [Phys. Rev. A 32 (1985) 332]. Shot-to-shot variations of the Stokes energy initiated by quantum noise are calculated and the probability distribution function of the pulse energy is shown to be of negative-exponential shape in a no-pump-depletion region. Output Stokes field is expanded into the coherent modes, and it is shown that the most significantly excited mode of the Stokes field contains more than 99% of the Stokes pulse energy. Shot-to-shot fluctuations of the mean frequency of the narrow-band Stokes field, whose linewidth is 100 MHz (FWHM), is 200 MHz; however, that of the broad-band Stokes field reaches 1 GHz.

Laser photoacoustic spectrometry for trace gas monitoring

Spectroscopic methods offer important features with respect to atmospheric trace gas monitoring. Some relevant techniques are briefly discussed. Emphasis is put on various aspects of photoacoustic spectrometry. Its basic principles and important experimental characteristics are outlined. Depending on molecular absorption cross-sections, a detection limit in the low ppbv concentration range is typically achieved without the use of any preconcentration device. In multi-component mixtures this limit may be increased owing to absorption interferences. Two photoacoustic (PA) systems have been developed and some specific applications are presented. A CO-laser PA system operating in the 5–6.5 µm wavelength range was applied to the analysis of motor vehicle exhausts. Apart from nitrogen oxides, CO2 and water vapour, ten different volatile organic compounds (VOCs) including o-, m- and p-xylene were selectively detected at parts per million by volume (ppmv) concentrations. As a second instrument, an automated CO2 laser PA system was implemented in a trailer for in situ measurements. It was applied to the detection of stack gases at a pharmaceutical plant and to air monitoring in urban and rural environments. As an example, ethene, ammonia and ozone were detected at ppbv concentrations in rural air. Finally, new aspects are discussed, in particular the introduction of CO2 isotopes as the laser medium, the design of PA Stark cells and the development of a continuously tunable high-pressure CO2 laser and of a widely tunable mid-infrared laser based on frequency mixing in a non-linear crystal. Although PA spectrometry already represents a valuable alternative to more established spectroscopic and non-spectroscopic schemes, these novel developments should further enhance its potential and versatility.

Intracavity active frequency shift: a novel method of shifting the frequency of pulsed lasers

We have developed a new technique for shifting the frequency of a TEA CO(2) laser that utilizes a Pockels cell in the main cavity and an acousto-optic frequency shifter in the subcavity. The amount of frequency shift was controllable by the gate pulse width of the Pockels cell. The maximum shift from the line center achieved was 1.4 GHz at the 10P(20) line, limited by the gain bandwidth. This method, which keeps the single-longitudinal-mode oscillation, can be widely applicable to pulsed lasers with a wide gain bandwidth, such as high-pressure CO(2) lasers.

100 ps far-infrared laser pulses from optically pumped D 2O

In this paper we report the generation of ultrashort far-infrared laser pulses with durations less than 100 ps, powers exceeding 200 kW and intensities of more than 1.5 MW/cm 2. Far-infrared radiation was produced via stimulated resonance Raman scattering using a high-pressure CO 2-laser as pump source and the heavy water isotopes D 2 16O and D 2 18O as far-infrared laser media. Pulses achieved from this laser system were detected by a novel type of detector, sensitive over a broad spectral range from the far-infrared to the visible, basing on quasiparticle heating in a strip-line structured YBa 2Cu 3O 7−δ thin film.

Mixing effect in the NH3 absorption and MIR emission spectra pumped by a continuously tunable CO2 laser

By tuning a high pressure CO2 laser (HPL) around strong ammonia lines nearly coincident with CO2 lines an of-fresonant absorption is observed which can be confirmed by the superfluorescent MIR emission. This effect is related to a two frequency v1, v3 HPL emission in the regime of moderate pulling. Around a strong absorption line a mixed v4=2v1−v3 frequency is produced that is strongly absorbed

A novel technique for synchronization of pre-ionizing and pumping currents for operation of high-pressure TEA CO2 lasers

The authors report a novel means of achieving synchronization between the pre- and main discharges, a pre-requisite for reliable operation of UV pre-ionized TEA CO2 lasers, by utilizing only a coupling inductance between these two discharge circuits. The inductance, whose value may be a few tens of mu H, can be constructed in the laboratory simply by winding a few turns of ordinary wire on any insulator.