Generation of narrowband tunable VUV radiation at the Lyman-α wavelength

Tunable narrowband VUV radiation has been generated at the Lyman-α wavelength $\text{λ =}\text{1216}\text{\&}\text{A}\text{ring}$; by frequency tripling in krypton the frequency-doubled output of a powerful dye laser system which is excited with the second harmonic of a Nd-YAG laser. 5 ns long UV dye laser pulses ($\text{λ =}\text{3646}\text{A}\text{?}$) of 1.8 MW peak power yielded VUV light pulses of 2.2 W (5.4 × 19⁹ photons/pulse). The bandwidth of the dye laser radiation could be narrowed to 8.7 × 10^-3cm^-1 (4.6 × 10^-3 Å). The expected bandwidth of the VUV is less than 5.2 × 10^-2cm^-1 (7 × 10^-4 Å). The tunable VUV radiation is used for the recording of the absorption spectra of the Lyman-α resonance transitions in atomic hydrogen and deuterium with doppler-limited resolution.     

Threshold of the 2ωpe instability in a laser produced plasma

$\text{3}\text{2}$ω_L emission from various plane targets irradiated by a 20 J, 5 ns neodymium laser pulse has been investigated. The onset of $\text{3}\text{2}$ω_L emission and an increase in intensity by five orders of magnitude is observed at a laser intensity of ≌2×10¹³W cm^-2, the threshold intensity predicted for excitation of the 2ω_pe instability.     

Preferential excitation transfer in Cs1(6D32)- Cs(6S12) collisions

A cw dye laser beam, tuned near the Cs 8761 Å resonance (Cs¹(6P_{$\text{1}\text{2}$}) → Cs¹(6D_{$\text{3}\text{2}$}) transition) is focused into a Cs vapor. At a Cs density higher than 5 × 10¹⁵ cm^-3, we observe a greater 6P_{$\text{1}\text{2}$} population when the laser is on resonance than when it is off resonance. However, at a lower Cs density, the reverse is observed. This phenomenon is explained as due to the preferential excitation transfer process: Cs¹(6D_{$\text{3}\text{2}$}) + Cs(6S_{$\text{1}\text{2}$}) → Cs¹(6P) + Cs¹(6P), and the corresponding cross secti on is estimated to be (1.5^+1.5_-0.7) × 10^-14 cm² by fitting the experimental results to an approximate rate-equation analysis.     

Superradiation from non-ideal plasmas in electric field

An effect of external static electric field on emission of radiation from non-ideal plasmas of erosion focus has been experimentally observed. An order-of-magnitude increase in radiation intensity for spectral interval hv = 40 ? 350 eV with electric field increasing up to 10³V/cm has been found for plasmas with $\text{ξ}\text{Z}\text{?1}$, where ξ is the number of electrons in Debye sphere, Z = 2 ? 3 is the stage of ionization. The energy emitted has been several times higher than the black body energy for the same spectral interval at maximum electric field achieved. The effect vanishes at $\text{ξ}\text{Z}\text{?10}$.     

A one-dimensional microscopic quantum mechanical theory of light enhanced desorption

A one-dimensional microscopic quantum mechanical model is used to inquire whether it is possible to enhance the desorption rate by employing a laser to induce vibrational excitation of the chemisorptive bond. For model parameters simulating CO/Cu it is found that the required laser intensity is very large, roughly 10⁴ times that of a conventional high power CO₂ laser (whose intensity we take to be $\text{5 × 10}{}^{10}\text{W}\text{cm}{}^2$). We suggest that surface roughness can be used to enhance substantially the effect of the laser and possibly to enable the observation of laser enhanced desorption.     

Determination of fraction of molecules excited by laser IR radiation

To explain the observed excitation by laser IR radiation of moderate intensity (I = 1?10 MW/cm²) of the many rotational states (much greater than $\text{Ed}{}_{\mathrm{<mtext>01</mtext>}}\text{2}\text{hcB}$) it is suggested that mixing of the ground state components of the common symmetry type (“N-mixing”) take place. Estimation of the fraction of molecules excited by multiphoton processes is in satisfactory agreement with an experiment.     

Tunable XUV radiation generated by nonresonant frequency tripling in neon

Nonresonant frequency tripling of ultraviolet (UV) radiation (λ_uv = 216–223 nm, generated by sum frequency mixing of the outputs of a frequency doubled pulsed dye laser and of the Nd-YAG pump laser) generates in neon coherent light in the extreme ultraviolet (XUV). The XUV radiation is tunable in spectral regions of negative dispersion λ_xuv = 72.05- 73.58 nm and λ_xuv = 74.3–74.36 nm at the high energy side of the transitions $\text{2p-3s′[}\text{built1}\text{2}\text{, 1]}$ and $\text{2p-3s[}\text{built3}\text{2}\text{, 1]}$. At UV input powers of 0.1-0.3 MW the generated XUV power was typically P_xuv = 0.1-0.4 W (1.5–6 x 10⁸ photons/pulse). Since present UV dye laser systems provide at λ_uv pulse powers of almost 1 MW the XUV output could easily be increased by more than one order of magnitude.     

Generation and amplification of nanosecond pulses by iodine lasers

Results are reported of experimental investigations of high-power photodissociation iodine laser pumped by lamps and by radiation from high-current electric discharges. The basic parameters of the working medium, the parameters of both lamp-pumped and discharge-pumped lasers, and methods of shaping of a short pulse with diffraction directivity of the radiation are investigated. The possibility of effective amplification of a short pulse by an iodine amplifier pumped with an open high-current discharge is demonstrated. An iodine laser generating a pulse of duration I nsec, divergence 10^-4 rad, and energy 100 J at a contrast 10⁸ and 300 J at a contrast 10²–10³ is described.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, 46–103, 1980.     

Level-crossing under nearly monochromatic excitation by a narrow-band cw dye laser

The shape of level-crossing signals under excitation by a narrow-band tunable dye laser has been investigated. The light of the laser was scattered on a highly collimated atomic beam of Na. The laser radiation (bandwidth about 3 MHz) was fairly monochromatic compared with the natural line-width of the 3 ²P_{$\text{3}\text{2}$} state (10 MHz). The form of the zero-field level-crossing signal of this state depends strongly on the frequency of the exciting radiation. The experimental results agree well with calculated signal shapes.     

Saturated absorption spectroscopy in the ultra-violet with a continuous-wave,frequency-doubled,ring dye laser; even isotope shifts on the 6d3D1-6p3P0 transition of HgI

A novel, single-frequency, continuous-wave, ring, dye laser with intra-cavity frequency-doubling has been developed, and used to carry out saturated absorption spectroscopy on the 6s6d³D₁-6s6p³P₀ transition of Hg I at 296.7 nm. Even isotope shifts have been measured by this technique on this transition and are: Hg204-202, 350 ± 10 MHz; Hg202-200, 345 ± 10 MHz; Hg200-198, 310 ± 10 MHz. The shift on transitions from the hyperfine state 6s6d³D₁ ($\text{F =}\text{3}\text{2}$) between Hg199 and Hg201 has also been measured, and is 225 ± 10 MHz.     

Measurements of the upper and lower level lifetime in He-Se lasers

The lifetimes τ₂ and τ₁ of the upper and lower levels of the 5227 Å (5p ⁴D_{$\text{7}\text{2}$}→5s ⁴P_5/2) laser transition in He-Se were measured. The obtained values are: τ₂=(18.5±1.85) × 10^-9 sec; τ₁=(2±0.4) × 10^-9 sec. The value of τ₂ was determined by measuring the time constant of the transient in the fluorescent emission consecutive to a sudden interruption of the laser oscillation inside the cavity.The value of τ₁ was determined by measuring the change induced by one laser transition on the unsaturated gain of another laser transition sharing the same lower level. Finally the “radiation trapping” factor is evaluated, thus ruling out the possibility that radiation trapping might be responsible for saturation in the laser output versus discharge current.     

Bound exciton luminescence of Ar- and Al-implanted ZnO

Argon- and aluminum-implanted ZnO single crystals (N_impl=10¹⁶?10¹⁹cm^?3) were investigated at liquid helium temperature by photoluminescence. We obtained highly resolved emission spectra of implanted and thermally annealed samples. Maximum luminescence yield was achieved after annealing with an oxygen ambient at 800°C and an anneal time of 30 min. In Al-implanted ZnO crystals, we observed a strong emission line $\text{I}{}_{\mathrm{<mtext>5</mtext><mtext>6</mtext>}}\text{at λ = 3688}\text{A}\text{?}$. The intensity of this line is correlated with the implanted Al concentration. The I_{$\text{5}\text{6}$} line is interpreted as the recombination of a bound exciton at a polycentric Al complex.     

Fine and hyperfine structure spectra of the ultra-violet 2 3S → 5 3P transition in 4He and 3He with a frequency doubled CW ring laser,detected via associative ionization

High resolution laser spectroscopy coupled to a sensitive method of detection via mass analysis of He⁺₂ ions produced in $\text{He(5}{}^3\text{P) + He(1}{}^1\text{S)}$ collisions, is used to obtain the fine and hyperfine spectra of the ultra-violet He 2 ³S → 5 ³P transition. A cw tunable UV radiation around 294.5 nm is generated by intracavity frequency doubling a Rhodamine 6G single mode ring dye laser using an ADA crystal. Both spectra enable fine and hyperfine structures to be determined within a few MHz. The magnetic dipole coupling constant A of the 5 ³P term of ³He is found to be -4326 ± 9 MHz (-0.1443 ± 0.0003 cm^-1).     

Tunable XUV radiation generated by nonresonant frequency tripling in argon

Nonresonant frequency tripling of the ultraviolet (UV) radiation of a frequency doubled pulsed dye laser generates in argon coherent radiation in the extreme ultraviolet (XUV). The radiation is tunable in spectral regions of negative dispersion λ_XUV = 97.4–104.75 nm, λ_XUV = 86.8–86.98 nm and λ_XUV = 85.7–86.68 nm located at the high energy side of the transitions 3p-4s′ [$\text{1}\text{2}$,1], 3p-5s′ [$\text{1}\text{2}$,1] and 3p-3d′ [$\text{3}\text{2}$,1], respectively. At UV input pulse powers of 1–2 MW the pr oduced. XUV power was typically 1–8 W (0.2–1.6 × 10¹⁰ photons/pulse).     

He atom diffraction from a silicide precipitate on a Pt(100) surface

We have observed the formation of an ordered silicide at the surface of a nominally pure Pt(100) crystal. The silicide appears after thermally activated migration of a trace Si impurity (<10^?4 at%) and subsequent cooling. The silicide is about one monolayer thick and forms a large area unit mesh, $\text{(6}\text{2}\text{×6}\text{2}\text{)R45°}$, which is observed with both He diffraction and LEED. A thermal attenuation analysis of the specular and a diffracted He beam yields a consistent value for the attractive depth of the He-surface potential D=13 meV. From a simple classical analysis of the He diffraction pattern we have obtained an estimate for the corrugation of the He-surface potential, $\text{ξ=0.07}\text{A}\text{?}$. The well depth D is shown to be consistent with the wavelength dependence of the angular distribution of the diffraction pattern.     

Study of Direct Amplification of Ultrashort Light Pulses in a Laser Amplifier with a View to Obtaining High Radiation Contrast

An amplification scheme for ultrashort laser pulses of high radiation contrast was used to perform experiments on ablation pressure symmetrization using a prepulse upon acceleration of thin foils. It is shown that the spontaneous radiation of the regenerative amplifier restricts the energy contrast in the amplification of chirped pulses at a level of 10^-4–10^-3. The possibility of direct amplification of a short pulse with a view to increasing the energy contrast ratio was considered. Experiments were performed on the PICO laser facility to demonstrate that a 10-ps pulse amplification achieved an intensity 100 GW/cm², a gain factor of 1.2, and an inversion dumping factor >30%.     

Plasma production in a Cs vapor by a weak CW laser beam at 6010 Å

When a dye laser beam at 6010.5 Å (which excites the $\text{Cs 6}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→8D}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ transition), of power 0.1 W, is focused into a Cs vapor of density ? 10¹⁷ cm^-3, we observe a bright localized white glow near the laser focus. Our experiments indicate that this glow is due to the production of a Cs plasma, which exhibits many characteristics of a discharge plasma, like emission of numerous atomic lines and of recombination continua, plasma-broadening of atomic lines, and hysterisis. This laser-produced plasma is in Saha equilibrium with a typical electron density of 3 × 10¹⁴ cm^-3, and a typical electron temperature of 0.2 eV.     

Rapid differential decay of metastable populations in a copper halide laser

The time dependences of the populations ofthe copper metastable levels (²D_{$\text{5}\text{2}$}, ²D_{$\text{3}\text{2}$} have been measured in a longitudinally-excited CuBr laser of tube diameter 12 mm at a dissociation energy density of 15 mJ cm^-3. The metastable populations are created within 3 μs of the dissociation discharge pulse and thereafter decay to the ground level by electron collisions. The decay of the ²D_{$\text{3}\text{2}$} population is faster than that of the ²D_{$\text{5}\text{2}$} population and, in the case of CuBr, both decay rates are increased significantly by the decomposition products which arise from the presence of cupric oxybromide as an impurity. Decay times for the ²D_{$\text{5}\text{2}$}, ²D_{$\text{3}\text{2}$} populations as short as 4, 1.8 μs respectively have been observed under optimum laser conditions. The increase in the relative intensity of the 578.2 nm line at the shortest interpulse delays (ca 10 μs) is due to the more rapid decay of the ²D_{$\text{3}\text{2}$} population. At times up to the several microseconds after the dissociation current pulse the gas in the laser tube remains highly conducting. The rise-time of the pumping pulse is then determined by the external circuit rather than by the transit time of an ionization wave. The controlled effect of the cupric oxyhalide impurity in both CuBr and CuCl lasers offers the prospect of more efficient operation of copper halide lasers at repetition rates in excess of 20 kHz.     

Studies of the red anti-stokes emission of erbium ions in the Y2O2S: Er,Yb phosphor system

Excitation of the anti-Stokes red emission radiation from erbium ions by 1000 nm radiation in the Y₂O₂S: Er, Yb system has been investigated using a range of samples with widely varying erbium but fixed ytterbium content. A square law intensity dependence is found favouring the models of Sommerdijk and of Hewes and Sarver. Comparison of Stokes and anti-Stokes excitations of both green and red erbium emissions then eliminates the Hewes and Sarver model. Studies using twin-beam excitation as by Kuroda et al. (1000 nm plus 1500 nm) and over a range of temperatures give evidence that the previous assumption of the non-radiative, multiphonon relaxation between the ⁴I_{$\text{11}\text{2}$} and ⁴I_{$\text{13}\text{2}$} states following the first 1000 nm excitation is not satisfactory and suggest that this transition is radiative (2500 nm radiation).