Iodine photodissociation laser with thermal gas flow

The sealed-off repetitive iodine laser with a thermal gas flow recirculation is described. Experimental results concerning the studies of the laser fuel flow velocity and output pulse energy are presented. With the repetition frequency of 1 Hz the output energy 450 ml was achieved.Paper presented at the Workshop on Iodine Photodissociation Lasers, Bechyn 1986, Czechoslovakia.We want to thank Dr. J. Musil from Institute of Physics for much valuable advice and support of the program.     

100 GW pulsed iodine photodissociation laser system PERUN I

The photodissociation iodine laser system PERUN I is described. The laser generates and amplifies the subnanosecond pulse with the energy about 80 J of the fundamental wavelength 1·315 μm and beam diameter 10 cm. The physical principles of this type of the high power laser are briefly explained and the laser system and its characteristics are described from the physical and technical point of view. Special attention is paid to the realization of such system with the slow optical pumping (≈300 μs).     

Diffraction-limited atomic iodine photodissociation laser

A high-reliability diffraction-limited atomic iodine photodissociation laser is described. It is shown that a diffraction-limited output beam is obtained when the laser pulse is extracted before the onset of gain-medium inhomogeneities caused by non-uniform deposition of the pump radiation. No degradation of the beam focusability is observed for intensities at which the final amplifier is heavily saturated.This work supported by the United States Department of Energy.     

Miniaturization of a thalliumiodide photodissociation laser

We report on the operation of a thallium photodissociation laser with an active medium in the form of a thin layer on a quartz wall. Laser emission has been obtained with layer thicknesses below 100 m. This gas laser seems to be feasible with an active volume as small as 10^–1 to 10^–2 mm³.     

Subnanosecond high-pressure iodine photodissociation laser oscillator

A simultaneously Q-switched and acousto-optic mode-locked high-pressure iodine photodissociation (=1.315m) oscillator system, capable of generating pulse-widths as short as 160 ps is described. Good agreement is found between theory and experiment for the pressure-dependence of the modelocked pulse-width. The results indicate that pulse-widths approaching 100ps should be obtainable with this type of system.     

Conversion to the second harmonic of high power iodine photodissociation laser system PERUN

The frequency doubling of the iodine laser PERUN is described. The maximum conversion efficiency of 55% is attained, the energy of the red (=0.657m) radiation is 20 J.     

Broadband femtosecond OPCPA system driven by the single-shot narrow-band iodine photodissociation laser SOFIA

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800?nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 10⁸ times. The amplified spectral bandwidth of 68?nm corresponds to the pulse duration of 14?fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (<0.1?cm^?1) and, therefore, the conventional chirped-pulse amplification technique does not lead to pulse durations at the femtosecond level.     

Power optimization of a Tl photodissociation laser

Conditions for the operation of a Tl photodissociation laser, in view of power optimization, have been determined. A crucial parameter is found to be quenching of the upper laser level. A value for the quenching cross-section of the 7² S _1/2 Tl state by the TlI molecules of 2×10^–14 cm² has been measured.     

On kinetics of the photodissociation iodine laser

The kinetics of iodine laser amplifiers is examined by solving the time evolution equations of chemical kinetics during optical pumping. The pumping radiation intensity is modelled by a black body of the temperature varying in time (corresponding to the flash lamp pulse). A brief comparison is made of pumping effects by long and short light pulses. Pumping by the long pulse is studied in more detail and it is found that there exists an optimum pulse strength beyond which the inversion in the laser mixture no longer grows appreciably, only its lifetime is shortened. In this connection the effect of pyrolysis of the alkyliodide molecule is also discussed. The pyrolysis is found to occur under very strong illumination, but it does not interfere with the photolytic decomposition and the optimum laser action. Finally, the influence of the reaction rate constants is studied in a systematic way and only few of them are found to carry real weight.The authors are obliged to Drs. S. V. Kuznetsova and A. I. Maslov who were consulted on the values of the reaction constants and who also drew our attention to some of the references.     

Atomic mercury photodissociation laser in the visible

Stimulated emission on two new pulsed laser lines in atomic mercury is reported. The laser emits at 435.8 and 546.1 nm, corresponding to the transitions 7 ³S₁ → 6 ³P₁ and 7 ³S₁ → 6 ³P₀ of the neutral atomic mercury atom. Population inversion is generated by photodissociation of HgI₂ vapor with a KrF laser at 248 nm. 150mJ of KrF laser radiation were focused into the HgI₂ cell by means of a cylindrical lens in a transverse pumping configuration. With a single end mirror pulses with a peak power of 3 kW and duration of approximately 1 ns were generated. The pumping mechanism is proposed to be a sequential three-photon process.     

Lasers excited by photodissociation: The thalliumiodide laser

This review is concerned with lasers excited by photodissociation of molecules. The principle of photolytic excitation is described and a number of existing lasers is presented. As an example the properties of the thallium laser such as spectral and temporal emission, achievable gain and efficiency are discussed in detail.     

Iodine stabilised 640 nm helium-neon laser

The wavelength of a helium-neon laser operating at 640 nm coincides with two strong absorption lines in the spectrum of iodine-127 when the gain tube is filled with neon-22. The absorption lines have been identified by measuring their hyperfine structure and the performance of the laser has been investigated. The beat frequency pair variance between two similar lasers was 7.6 kHz for a 10-second averaging time and the wavelength of component g of the 8-5 P(10) line was measured as 640.2834686 nm.     

Kinetics of the photodissociation iodine laser with slow pumping

Systematic calculations of maximum inversion were performed for iodine photodissociation laser in dependence on the mixture composition. The flash-lamp radiation was modelled as emanating from an optically thin Xe plasma. Duration of the pumping pulse is about 300 s. The sensitivity of the model to the values of kinetic constants was also tested.     

Investigation of emission characteristics of a photodissociation thallium laser

Results are reported of investigations of the spectral and energy properties of the emission of a thallium laser on the transitions 7S_1/2-6P_3/2 ( = 535 nm) and 7S_1/2-6P_1/2 ( = 377.6 nm). Excited thallium atoms are produced in dissociation of the TII molecule by radiation from an ArF laser (I = 193 nm). The experiments were performed with two cavity types, to make possible operation with lasing at one or two wavelengths. In the case of operation with one wavelength, the emission spectrum at = 535 nm consists of the hyperfine structure components of two isotopes T1²⁰³ and T1²⁰⁵ whose frequency difference depends on the emission flux density in the cavity. At the = 377.6–nm wavelength the isotopic structure of the line is not manifested, since the isotope shift is small compared with the Doppler width. When two wavelengths are generated, it is observed that when a certain flux density is reached the emission structure is qualitatively altered, with unequal changes in the character of the emission spectra of the different lines. The results are discussed.Translated from Lazernye Sistemy, pp. 58–66, 1982.     

Oxyhemoglobin photodissociation efficiency in biological tissue exposed to laser radiation

We have obtained quantitative data on the differential (with respect to depth) and the integrated oxyhemoglobin photodissociation efficiency in the dermis when the skin surface is exposed to a light beam in the wavelength range 300–650 nm. With this aim, we have used our own previously developed optical model for skin tissue and analytical procedure for calculating the characteristics of optical fields in a medium. We have estimated the number of oxygen molecules formed at different depths in the medium, and also their integrated number over the entire thickness of the dermis as a function of the irradiation wavelength. We consider models for a dermis that is homogeneous with respect to depth and a dermis that has a layered structure. We show that the spectral photodissociation efficiency has a number of maxima associated with the absorption spectrum of oxyhemoglobin and the optical properties of all the layers of skin tissue. We discuss the effect of the epidermis on these maxima.     

Iodine laser production of highly charged Ta ions

The results of systematic studies of multiply charged Ta ion production with the fundamental frequency of an iodine laser (=1.315m), and its 2nd (0.657m) and 3rd (0.438m) harmonics are summarized and discussed. Short laser pulse (350 ps) and a focus spot diameter of 100m allowed for the laser power densities in the range of 5×10¹³–1.5×10¹⁵ W/cm². Corpuscular diagnostics were based on time-of-flight methods; two types of ion collectors and a cylindrical electrostatic ion energy analyzer were used. The Ta ions with charge state up to 55+ were registered in the distance of 210 cm; the maximum amplitude of the signal of a high energy ion group was found to belong to the ions with the charge state around 43+, depending on the laser power density. The ion energy distribution was measured for all three wavelengths, however, in a different energy range; the maximum registered ion energy was 8.8 MeV. The occurrence of highly charged ions in the far expansion zone is discussed in view of the mechanism of charge distribution freezing during two-temperature isothermal plasma expansion.The work was performed in a partial fulfillment of the research grant project No. A1010525 sponsored by the Academy of Sciences of the Czech Republic and grant project No. 202/95/0039 sponsored by the Grant Agency of the Czech Republic.     

Conversion to the third harmonic of the iodine photodissociation laser PERUN

The frequency tripling of the iodine laser PERUN is described. The maximum conversion efficiency to the third harmonic is 50%, which represents about 20 J of the 3 laser beam.     

Isotopic selectivity of IR laser photodissociation of CF3I molecules

The selectivity dependence of multiphoton dissociation of CF₃I on the conditions of excitation (pulse duration, concentration of the isotope under excitation and gas pressure) has been studied. It has been shown that the main mechanism of selectivity loss isV-V exchange during a laser pulse. The elaborated model is in good agreement with the experiment.     

Spectral properties of a HgBr2 photodissociation laser

A small-size HgBr₂ photodissociation laser is operated without buffer gas. It is shown, that in the laser emission as well as in the flourescence spectrum, excited with the wavelength of an ArF laser at 193 nm, approximately the 10 lowest-lying vibrational levels of the $\text{B}{}^2\text{Σ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{+}}$ state contribute to the emission.