Flashlamp Excitation Research Articles

Time-resolved measurements of statistics for a Nd:YAG laser

Time-resolved measurements of the fluctuating intensity of a multimode frequency-doubled Nd:YAG laser have been performed. For various operating conditions the enhancement factors in nonlinear optical processes that use a fluctuating instead of a single-mode laser have been determined up to the sixth order. In the case of reduced flash-lamp excitation and a switched-off laser amplifier, the intensity fluctuations agree with the normalized Gaussian model for the fluctuations of the fundamental frequency, whereas strong deviations are found under usual operating conditions. The frequencydoubled light has in the latter case enhancement factors not so far from values of Gaussian statistics.

Two-pulse dye laser with flashlamp excitation

Two-pulse operation was achieved in a high-power organic-dye laser excited by a coaxial flashlamp. The conditions essential for achieving such operation were identified. The minimum interval between the pump pulses, set by the damage to the outer quartz tube of the coaxial flashlamp, was determined.

A Fiber‐Optic System for Measuring Single Excitation‐Dual Emission Fluorescence Ratios in Real Time

AbstractThe development and subsequent evaluation of a fiber‐optic system for measuring single excitation—dual emission fluorescence ratios in real time is described. The design of the flashlamp excitation source, optics, electronics, and computer software is discussed. The dual emission pH sensitive fluorophore 1, 4‐dihydroxyphthalonitrile (1, 4‐DHPN) was used to test the performance of this system. The flexible design of this modular system permits the use of other single excitation—dual emission fluorophores by simply changing the appropriate optical filters. Upon a single 340–380‐nm excitation, pH‐sensitive emissions were monitored at 488 nm and 434 nm. The ratio of these emissions (488/434) was then computed in real time, for a 2 mM solution of 1, 4‐DHPN, while the pH was titrated over the range 5–9. The nonlinear, system‐dependent, calibration curve of pH versus the ratio of emission wavelengths was empirical fit by a fourth‐order polynomial (r2 = 0.995). Reliable pH measurements in the range 6–8 were obtained using concentrations of 1, 4‐DHPN as low as 50 μM. The standard deviation of pH measurements using a 1 mM solution of 1, 4‐DHPN, near neutral pH, was found to be approximately 0.1 pH unit.

Bimolecular cyclization of di- p-tolylamine to 2,7-dimethylacridine in the presence of bromoform: microsecond flash photolysis study

The UV irradiation of di- p-tolylamine and bromoform results in the formation of 2,7-dimethylacridine (with a quantum yield of 0.20 ± 0.04). The primary transient spectrum (λ max ≈ 700 nm), recorded following microsecond flash lamp excitation, can be attributed to the amine cation radical and, probably, the neutral diarylnitrogen radical, which arises from the former on deprotonation. Both of these radicals can recombine with the dibromomethyl radical to give the intermediate IM1. This is transparent in the visible region of the spectrum and is transformed into the second intermediate IM2 (λ max ≈ 540 nm), which finally gives rise to acridine. The observed first-order rate constant of IM2 formation is dependent on amine concentration, indicating the participation of an additional amine molecule in the transformation of IM1 to IM2. A new reaction scheme is proposed which assumes that the attack of the alkyl radical is predominantly directed towards the nitrogen atom of the amine radical.

Emission spectra and cross-section spectra of neodymium laser glasses

Amplified spontaneous emission spectra and light amplification spectra of some Nd3+:glass rods (silicate glass Schott LG680, phosphate glasses Schott LG760 and Hoya LHG5) are measured by pulsed flashlamp excitation. The spontaneous emission distribution, the stimulated emission cross-section spectra and the excited state absorption cross-section spectra are extracted. Excited state absorption prevents laser action around 1320 nm for the 4 F 3/ 2 - 4 l 13/ 2 transition of Nd 3+ in the investigated glasses.

Pulsed dye laser lithotripsy--currently applied to urologic and biliary calculi.

The flash lamp excitation of coumarin dye to produce light energy of the specific wavelength of 504 nm is the basis for the new wave of pulsed dye lasers. Numerous urological applications have been developed. Treatment of ureteral and renal calculi has proven to be an atraumatic and effective treatment modality. Most recently, this technology has been applied to the endoscopic treatment of biliary calculi. The authors review the most recent treatment techniques in both biliary and urinary stone disease.

Laser action from 2,6,8-trisubstituted-1,3,5,7-tetramethyl-pyrromethene-BF_2 complexes: part 2

In laser activity 1,3,5,7-tetramethyl-2,6-dicarboethoxy-8- cyanopyrromethene-BF(2)complex 5 under flash-lamp excitation was approximately 1.8 times more energy efficient than Rhodamine-B; about the same efficiency of Rhodamine-575 was found for 1,3,5, 7-tetramethyl-2,6,8-triethylpyrromethene- BF(2) complex 2.

Relationship between vasopressin-sensitive water transport and plasma membrane fluidity in kidney collecting tubule

The role of plasma membrane fluidity in the regulation of kidney tubule water permeability has been uncertain. We have used new methods to image the fluorescence anisotropy of fluidity-sensitive fluorophores (Fushimi, Dix, and Verkman. Biophys. J. 57: 241-254, 1990) to quantitate membrane fluidity in cells of the vasopressin-sensitive cortical collecting tubule (CCT) and water-impermeable cortical thick ascending limb (CTAL). Isolated tubule segments from rabbit kidney were perfused in vitro, and apical or basolateral plasma membranes were stained with trimethylammonium diphenylhexatriene (TMA-DPH). TMA-DPH anisotropy (r) was imaged quantitatively by an epifluorescence microscope equipped with rotatable polarizers; TMA-DPH nanosecond lifetime (tau) was measured by flash-lamp excitation and gated photomultiplier detection. In CCT, apical membrane r (0.254 +/- 0.003) was similar to basolateral r (0.252 +/- 0.005). Serosal vasopressin at a dose that increased water permeability greater than 10-fold (250 microU/ml) did not affect apical membrane r (delta r = 0.002 +/- 0.003; 7 tubules). A 0.002 change in r was less than that produced by a 2 degrees C temperature variation. In CTAL, apical membrane r was 0.249 +/- 0.002, similar to r from basolateral membrane of proximal tubule (0.24), but much less than that of proximal tubule apical membrane (0.29). These results establish methodology to quantitate fluidity in intact kidney tubule segments and provide the first measurements of plasma membrane fluidity in CTAL and CCT. Our results suggest that regulation of bulk membrane fluidity in CCT apical membrane is not a component of the hydrosmotic action of vasopressin and that low apical membrane fluidity is not responsible for the low water and NH3 permeabilities in CTAL.

Pyrromethene–BF2 complexes as laser dyes:1.

AbstractCondensations between 3‐X‐2,4‐dimethylpyrroles (X = H, CH3, C2H5, and CO2C2H5) and acyl chlorides gave derivatives of 3,5,3′,5′‐tetramethylpyrromethene (isolated as their hydrochloride salts): 6‐methyl, 6‐ethyl, 4,4′,6‐trimethyl, 4,4′‐diethyl‐6‐methyl, and 4,4′‐dicarboethoxy‐6‐ethyl derivatives for conversion on treatment with boron trifluoride to 1,3,5,7‐tetramethylpyrromethene–BF2 complex (TMP–BF2) and its 8‐methyl (PMP–BF2), 8‐ethyl, 2,6,8‐trimethyl (HMP–BF2),2,6,‐diethyl‐8‐methyl (PMDEP–BF2), and 2,6‐dicarboethoxy‐8‐ethyl derivatives. Chlorosulfonation converted, 1,3,5,7,8‐pentamethylpyrromethene–BF2 complex to its 2,6‐disulfonic acid isolated as the lithium, sodium (PMPDS–BF2), potassium, rubidium, cesium, ammonium, and tetramethylammonium disulfonate salts and the methyl disulfonate ester. Sodium 1,3,5,7‐tetramethyl‐8‐ethylpyrromethene‐2,6‐disulfonate–BF2 complex was obtained from the 8‐ethyl derivative of TMP–BF2. Nitration and bromination converted PMP–BF2 to its 2,6‐dinitro‐(PMDNP–BF2) and 2,6‐dibromo‐ derivatives. The time required for loss of fluorescence by irradiation from a sunlamp showed the following order for P–BF2 compounds (10−3 to 10−4 M) in ethanol: PMPDS–BF2, 7 weeks; PMP–BF2, 5 days; PMDNP–BF2, 72 h; HMP–BF2, 70 h; and PMDEP–BF2, 65 h. Under similar irradiation PMPDS–BF2 in water lost fluorescence after 55 h. The dibromo derivative was inactive, but each of the other pyrromethene–BF2 complexes under flashlamp excitation showed broadband laser activity in the region λ 530–580 nm. In methanol PMPDS–BF2 was six times more resistant to degradation by flashlamp pulses than was observed for Rhodamine‐6G (R‐6G). An improvement (up to 66%) in the laser power efficiency of PMPDS–BF2 (10−4 M in methanol) in the presence of caffeine (a filter for light <300 nm) was dependent on flashlamp pulse width (2.0 to 7.0 μsec).

Laser action from 2,6,8-position trisubstituted 1,3,5,7-tetramethylpyrromethene-BF_2 complexes: part 1

Of the four new pyrromethene derivatives studied, 1,3,5,7,8-pentamethyl-2,6-diethylpyrromethene-BF(2) complex lased ~3 times more efficiently than rhodamine 560 under flashlamp excitation.

Temperature dependence of flashlamp-pumped Nd:YAG and Nd:Cr:GSGG lasers

Thresholds and slope efficiencies of Nd:YAG were compared to those of Nd:Cr:GSGG at temperatures ranging between 30– 300 K, using single shot flashlamp excitation. At room temperature, slope effieciencies of Nd:Cr:GSGG are about twice that of Nd:YAG while the thresholds are about the same. Both slope efficiencies and thresholds are reduced in the case of Nd:YAG when cooling from 300 to 80 K. Nd:Cr:GSGG seems to be temperature independent. The implications of the differing features of Nd:YAG versus Nd:Cr:GSGG are discussed.

Mathematical modeling of energy processes in YAG:Er3+lasers

A comparison of theoretical and experimental results shows that a suitable selection of the spectroscopic parameters of YAG:Er3+ crystals can ensure a qualitative agreement between calculations and experiments (within the limits of the relevant errors). Calculations demonstrate a considerable contribution of direct pumping of the upper active level by flashlamp excitation. The maximum theoretical value of the differential efficiency for the best laser head is 2.7%.

Efficient laser action from 1,3,5,7,8-pentamethylpyrromethene-BF 2 complex and its disodium 2,6-disulfonate derivative

We observed efficient laser action under flashlamp excitation at 546 nm from 1,3,5,7,8-pentamethylpyrromethene-BF 2 complex (PMP-BF 2), dissolved in ethanol. This new laser dye lased about 300% more efficiently than coumarin 545. The fluorescence, absorption (S-S) and triplet-triplet absorption spectra of PMP-BF 2 were also recorded. To achieve greater water solubility the disodium 2,6-disulfonate derivative (PMPDS-BF 2) was prepared. PMPDS-BF 2 lases about 3/4 as efficiently as PMP-BF 2 when dissolved in water and showed some photoinstability; however, in methanol it was highly resistant to photodegradation.

ACRYLAMIDE QUENCHING OF TRYPTOPHAN PHOTOCHEMISTRY AND PHOTOPHYSICS

Studies of acrylamide quenching of tryptophan (Trp) fluorescence, photochemistry, and photoionization have been conducted. Quenching of Trp fluorescence in aqueous solution by addition of acrylamide in the concentration range 0.0-0.5 M was measured and resulted in a Stern-Volmer quenching constant of KSV = 21 +/- 3 M-1. Photolysis experiments were performed in which Trp was photolyzed at 295 nm in the presence of varying concentrations of acrylamide. The loss of Trp was monitored using reverse-phase high performance liquid chromatography (RP-HPLC) and was observed to follow first order kinetics. Production of N-formylkynurenine (NFK) was observed by RP-HPLC in irradiated Trp samples both in the presence and absence of added acrylamide. In addition, no new photochemical product was detected. This was taken as evidence that acrylamide did not alter the photochemical pathway but just reduced the reaction rate as expected for a physical quenching mechanism. Plotting the reciprocal of photolysis rate constant versus acrylamide concentration produced a Stern-Volmer constant for quenching of Trp photochemistry of KSV = 6 +/- 2 M-1. The KSV values for both fluorescence quenching and photolysis quenching were thus large, implying efficient quenching of both processes by acrylamide. Assuming an excited singlet state lifetime of 2.8 ns, the calculated second-order quenching rate constants for fluorescence and photolysis were kq = 7.5 x 10(9) and 2.1 x 10(9) M-1 s-1 respectively. The possible involvement of photoionization in the photolysis mechanism was investigated by studies of acrylamide quenching of voltage transients produced by xenon flash lamp excitation of Trp at aqueous/teflon or aqueous/mica interfaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of the components of a binary solution to stimulated emission due to flashlamp excitation

A study was made of the contribution of electronic excitation energy transfer processes and the gain factor to the stimulated emission from various ethanol solutions of rhodamine and oxazine dyes due to flashlamp excitation. A method is proposed for calculation of the power density of the radiation absorbed by the acceptor molecules taking into account energy transfer from the donor to the acceptor and overlap of their gain spectra. Estimates are also made of the direct contribution of the excited donor molecules to the stimulated emission flux in the acceptor band. The calculated values are compared with the relative change in the output power of the mixture due to the introduction of a donor component into the active solution.

Intracavity spectrum analyzer based on LiF with flashlamp excitation of color centers

A single excitation source (in the form of a xenon flashlamp) was combined with spectral converters to demonstrate lasing due to F2, F2+, and F2− color centers in LiF. A universal spectrum analyzer for the investigation of gases and plasmas was constructed. Polychromatic quasi-cw lasing was excited by flashlamp pumping of color centers and this made it possible to widen the spectral range of the analyzer and to increase its sensitivity. The results indicated that it should be possible to construct soft apertures and switches (shutters) for visible laser radiation.

Dye laser with an output energy of 1 J, a beam divergence of 0.3 mrad, and flashlamp excitation

A study was made of the use of an unstable telescopic resonator in a laser utilizing an ethanol solution of rhodamine 6G excited by a coaxial transverse-discharge flashlamp. When the stored electrical energy was 300 J, the output energy of the laser was 1 J and the angle of divergence of the beam at half the maximum energy was 0.3 mrad. A mode structure of the radiation was observed within the limits of this angle and it was found that, in addition with the lowest symmetric modes, modes with a nonzero azimuthal index were generated. The kinetics of thermooptic distortions of the active medium was also investigated.

Syn-dioxabimanes as laser dyes I

Under flashlamp excitation, we observed laser action from 9, 10-dioxa-μ-bis(carboethoxy) methylene- syn-(methylene,methyl) bimane at 507 nm and 9, 10-dioxa- syn-(acetoxymethyl,methyl) bimane at 514 nm. 9, 10-dioxa- syn-(fluoromethyl,methyl) bimane showed weak laser action at 525 nm when dissolved in water, but also lased at 435 nm when dissolved in p-dioxane. Some spectroscopic data, such as absorption, triplet-triplet absorption, and fluorescence spectra of the new laser dyes are presented. The laser action properties of the syn-bimane laser dyes were compared to those of Coumarin 30.

New efficient dyes for the red part of the lasing spectrum

An investigation was made of the spectral, fluorescence, and lasing characteristics of two compounds of benzopyran derivatives with a condensed benzimidazole ring that emit in the 610–660 nm range under flashlamp excitation. The efficiency and photostability of the synthesized derivatives were several times better than those of the known xanthene dyes rhodamine C and rhodamine 101. Quantum chemical calculations using the π electron approximation were used to estimate the localization of the electronic excitations in molecular fragments.

Laser action from s y n-(methyl,chloro) bimane

Laser action under flashlamp excitation of syn-(methyl,chloro) bimane, dissolved in trifluoroethanol, was observed at 516 nm. This new dye lases about 60% as efficiently as coumarin 30. The heavy atom effect, as related to the laser action properties of syn-(methyl,chloro) bimane, is discussed. The concentration dependence on the laser output of the new laser dye was studied. The spectral location of the fluorescence maximum as a function of the syn-(methyl,chloro) bimane concentration was measured. The effect of solvent mixture ratio on the lasing wavelength of syn-(methyl,chloro) bimane was studied. Different options available for further improving the laser-action properties of syn-bimanes are presented.