Molecular gases as a source of coherent,tunable XUV radiation

Coherent and broadly tunable over 3500 cm^-1 extreme ultraviolet (XUV) radiation from 935 to 967 Å has been generated by frequency tripling the second harmonic output of a rhodamine 590 pulsed dye laser in molecular nitrogen and carbon monoxide. The scheme exploits high lying Rydberg and valence states of these gases and leads to the production of about 5 × 10⁹ XUV photons per pulse corresponding to a conversion efficiency of 5 × 10^-6.     

High power narrowband pulsed dye laser oscillator-amplifier-system

Construction details and operating characteristics are reported for a pulsed dye laser oscillator followed by a three-stage dye laser amplifier. The system is excited with 220 mJ of the second or120 mJ of the third harmonic radiation of a Nd-YAG laser. With Rhodamine dyes the output energy exceeds 55 mJ (9 MW peak power). Coumarin dyes provide pulses of more than 15 mJ (3 MW). Spectral narrowing to less than 260 MHz or 2.7 × 10 ^-4 nm at 565 nm is achieved by a single intracavity etalon of 37.5 GHz free spectral range. Gas pressure tuning allows a continuous linear variation of the laser frequency over more than 3.9 × 10³ GHz (4 nm at 565 nm). The frequency doubled laser output provides tunable UV light of narrow bandwidth (1.4 × 10^-4 nm) and of peak powers exceeding 3 MW.     

The generation of tunable coherent radiation in the wavelength range 2300–3000 Å using lithium formate monohydride

The generation of continuously tunable UV radiation in the wavelength range 2300–3000 Å by frequency doubling the output of a nitrogen pumped dye laser is described. A lithium formate monohydride crystal 10 mm long yields a conversion efficiency of typically 2% at fundamental powers in excess of 50 kW and allows the generation of harmonic radiation at wavelengths 150 Å below those attainable using a refrigerated ammonium dihydrogen phosphate crystal.     

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.     

在BBO中获得230.8—223.2nm高功率和频输出

用Q-YAG泵浦的Rh·6G染料激光在一块45°切割的β-BaB₂O₄(BBO)晶体中倍频,产生294.8—282.5nm范围的连续调谐输出,其能量为8mJ(在285nm处)。用这个倍频光与泵浦染料后剩余基波(1064nm)在另一块45°切割的BBO中和频,已获得230.8—223.2nm范围的连续调谐输出,其能量为120μJ,相应的峰值功率为12kW。还简述了获得高功率和频输出的关键技术。     

A simple,efficient plastic dye laser

A simple efficient plastic dye laser is described. A conversion efficiency of 47% was obtained from Rhodamine 6G doped PMMA, when pumped by the second harmonic of a Q-switched Nd: YAG laser in a near longitudinal pumping configuration. Lifetime tests performed on 0.3 cm² surface area of plastic, indicates a drop in efficiency from an initial 47% to 25% after 3.2 × 10⁴ shots. By defocusing the pump beam and doubling the sample thickness, the lifetime increases to 1 million shots before the dye laser efficiency drops from an initial 35% to 25%, for a scanned area of 2 cm², similar results have been obtained with rhodamine B.     

Production of high power tunable UV laser emission by second-harmonic generation fro, a rhodamine 6G dye laser

The generation of tunable UV radiation in the 280–310 nm range by doubling the output frequency of a flashlamp-excited Rhodamine 6 G dye laser is described. By using KDP and ADP crystals, conversion efficiencies of respectively 9.4% and 8.4% are obtained with UV output energies up to 50 mJ.     

Harmonic and sum-frequency generation of pulsed laser radiation in BBO,LBO, and KD*P

The optical properties of the nonlinear crystals lithium borate (LBO), barium borate (BBO) and deuterated potassium phosphate (KD*P) are compared for second and third harmonic generation of Nd:YAG laser radiation. In an experimental investigation the conversion efficiency has been measured as a function of the energy density of 8 ns long laser pulses, generated by a commercial Nd:YAG oscillator-amplifier system. In LBO and BBO the second harmonic generation saturates at an energy density of about 1.5 J cm^–2 at efficiencies of 55–60%. In KD*P comparable efficiencies (40–55%) require energy densities of 2–2.6 J cm^–2. Similar results are obtained for frequency tripling. In LBO and BBO saturated efficiencies of 20–25% are measured at an energy density of about 1.5 J cm^–2. In KD*P efficiencies of 20% are obtained at energy densities exceeding 2 J cm^–2. Besides for doubling and tripling of Nd:YAG laser radiation the phase-matching is calculated for frequency conversion of tunable laser light. The results demonstrate that in LBO and BBO phase-matched sum-frequency mixing of UV and infrared laser light generates tunable radiation at wavelengths as short as the transmission cut-off at 160 nm and 190 nm, respectively.     

Generation of tunable coherent VUV radiation by anti-Stokes Raman scattering of excimer-pumped dye laser radiation

A straightforward method of generating tunable coherent VUV radiation is described. Radiation down to 1362 Å was produced by Raman shifting the output of a commercially produced, excimer-pumped dye laser system. It is shown that generation of VUV radiation at 1640 Å is more efficient using the 8th anti-Stokes line from a UV dye than by using the 10th anti-Stokes line from a visible dye which had twice the output power.     

Efficient generation of tunable VUV laser radiation below 205 nm by SFM in BBO

Design and performance characteristics of a tunable dye laser system for sum frequency mixing (SFM) in a BBO crystal are presented. The system is composed of two tunable pulsed dye lasers pumped synchronously by the second harmonic of a commercial Nd:YAG laser. The radiation produced by the first dye laser is frequency doubled by second-harmonic generation (SHG) in KDP and subsequently mixed by SFM in BBO with the light of the second dye laser. The interest was focussed on generation of tunable laser radiation below 205 nm with high output power and long-time wavelength stability. High conversion efficiencies enable output energies of 100 J (20 kW) at 196 nm using only moderate Nd:YAG pump energies of 67 mJ. Altogether, a laser system with very good specifications for analytical application in the near VUV spectral region is reported.     

Direct observation of the two-photon generation of free excitonic molecules in CuCl

Two-photon absorption spectra due to excitonic molecule generation in thin CuCl samples at 4.2°K are directly measured using the intense light from a pulsed, frequency tunable dye laser. One narrow induced absorption peak is observed at 3893 Å. This peak exhibits a Fano interference line profile at low laser light intensities. High laser light flux densities result in a saturation, broadening, and blue shift of the induced absorption peak. The maximum value of the two-photon absorption cross section is directly measured to be 2 x 10^-43 cm⁴ sec, and the binding energy of the molecule is found to be 39 meV.     

Generation of coherent tunable deep UV radiation for detection and absorption studies of explosives RDX and TNT

We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200–260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600–700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47·10⁻⁹ M, whereas that for TNT is 35.7·10⁻⁹ M. The data were obtained using only ∼100 μJ/pulse of laser energy. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 516–521, July–August, 2007.     

Tunable cw infrared radiation by noncollinear difference-frequency mixing

Tunable cw infrared radiation has been generated by non-collinear difference-frequency mixing in LiJO₃, using the intracavity radiation of a Nd:YAG laser and the output of a Rhodamine 6G dye laser. Infrared powers of ∽35 μW tunable from 1.28 μm to 1.62 μm have been obtained.     

Generation of tunable picosecond pulses in the ultraviolet region down to 197 nm

Tunable picosecond pulses in the ultraviolet region down to 197 nm with ? 20 kW peak power are generated by the sum frequency mixing of fourth or third harmonic pulses of a mode-locked YAG laser with tunable pulses produced by a LiNbO₃ parametric oscillator pumped by second harmonic pulses of the YAG laser by using a KB5 or KDP crystal.     

The nonlinear optical susceptibility χ(2) near the bandgap in CdS

We have measured the second harmonic intensity generated in ultrapure CdS crystals using a tunable dye laser. The fundamental frequency corresponding to the bandgap was tuned over the various exciton energy levels. An analysis shows that at laser intensities necessary to observe second harmonic signals high excitation phenomena are unavoidable. At these intensities the excitonic contributions to the nonlinear optical susceptibility χ₍₂₎ are quenched by high excitation effects.     

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).     

Experiment Study of Dual Wavelength and Dual Pulse Q-switched Intracavity Frequency Doubling of a Tunable Cr:LiSAF Laser

In this paper, a flashlamp-pumped Q-switched Cr: LiSAF laser system with intracavity frequency doubling is designed to obtain dual pulse and dual wavelength laser output. The behaviors of second harmonic output of dual pulse and dual wavelength are studied experimentally. Good results are obtained in experiments: the output energy of each second harmonic pulse a round 448.1 nm is 10.2 mJ, the dual pulse time interval can be tuned widely, and the tunable range of each second harmonic wavelength is 448.1 to 465 nm.     

Experimental Study on Intracavity SHG of a Q-Switched Tunable Cr:LiSAF Laser

In this paper, a Q-switched intracavity frequency doubling Cr: LiSAF laser is reported. The relation of laser output behaviors with input energy was studied experimentally. The second harmonic output energy of 15.6 mJ at 450.1 nm for pumping energy of 83 J, the second harmonic output energy of 16 mJ at 445.1 nm for pumping energy of 75 J, and a tunable range of 445.1 ～465.1 nm were obtained in experiments.     

Tunable UV-radiation by stimulated Raman scattering in hydrogen

We observed tunable UV radiation down to 175 nm by SRS of the output of a frequency-doubled dye laser in H₂. The high power output of the 4th anti-Stokes to 5th Stokes line generated by the frequency doubled dye laser and the 8th anti-Stokes to 3rd Stokes line generated by the undoubled dye laser represents a broadly tunable coherent radiation source between 189 nm and 2064 nm.     

Experimental Study on Intracavity SHG of a Q-Switched Tunable Cr: LiSAF Laser

In this paper, a Q-switched intracavity frequency doubling Cr: LiSAF laser is reported. The relation of laser output behaviors with input energy was studied experimentally. The second harmonic output energy of 15.6 mJ at 450.1 nm for pumping energy of 83 J, the second harmonic output energy of 16 mJ at 445.1 nm for pumping energy of 75 J, and a tunable range of 445.1 ～465.1 nm were obtained in experiments.