Laser Stark Research Articles

Infrared Laser Stark Spectroscopy of Methyl Fluoride in 4He Nanodroplets.

We measured the rotationally resolved infrared spectra of helium solvated methyl fluoride at 3 μm and 10 μm, wherein lies C-H and C-F stretching bands, respectively. The linewidths (FWHM) were found to increase with increasing vibrational energy and range from 0.002 cm-1 in the v3 band (C-F stretch) at ~1047 cm-1, to 0.65 cm-1 in the v4 band (asymmetric C-H stretch) at ~2997 cm-1. In between these two bands we observed the lower and upper components of the Fermi triad bands (ν1/2ν2/2ν5) at ~2859 and ~2961 cm-1. We carried out Stark spectroscopy on the lower band on account of its narrower linewidths (0.04 vs. 0.14 cm-1, respectively). The objective of performing Stark spectroscopy was to see if there is any evidence for a rotational linewidth dependence on the external field strength, due to a reduced difference in between methyl fluorides rotational energy gap and the roton-gap of superfluid helium. We did not find any evidence for such an effect, which we largely attribute to the rotational energy gap not increasing significantly enough by the external field. We point to another molecule (formaldehyde) whose energy levels are predicted to show a more promising response to application of an external field.

Eradication of hairy mouth after oncological resection of the tongue and floor mouth using a diode laser 808 nm. Postoperative pain assessment using thermal infrared imaging.

Vascularized soft tissue flaps are often harvested from hair-bearing areas, such as the radial forearm or anterolateral thigh, making their use in oral reconstruction problematic due to postoperative hair growth. The presence of intact hair follicles in free tissue transfer and continued hair growth at the recipient site can result in difficulties with oral hygiene, intraoral irritation, food trapping, and patient distress. This study was to evaluate the intraoral efficacy and safety of a diode laser 808 nm when used for hair removal. Sixteen male patients, between 2010 and 2017, were referred for intraoral hair eradication with a history of squamous cell carcinoma of the tongue or floor mouth resection. An 808 nm diode laser (Stark 808, Plume s.r.l., Rome, Italy) was used to remove the intraoral hair. Each patient received a total of six treatments at 4-week intervals. Perifollicular pain was quantified by the physician using visual analog scales. Follow-up visits were scheduled at 1, 4, and 6 days to check the state of the tissues. The recall program included assessments of VAS, erythema, and perifollicular temperature. Patients were followed up for long-term assessments at 6 and 12 months after the final treatment session. All patients presented well with no occurrence of symptoms, indicating possible perifollicular inflammation. Based on the VAS scores, very mild discomfort during laser irradiation was recorded in all patients, with average pain score of 10.98 ± 1.42. No pain or discomfort was recorded 1, 4, and 6 days after the procedure. After the third pulse of light was applied, the average temperature with standard deviation of the hair tip with both the dark and light skin was 74.4 ± 11.7°C. The difference in temperature before the procedure (basal measurement 37.5 ± 2.8°C) and immediately after laser irradiation was 36.9 ± 3.7°C. The difference in temperature disappeared after 0.29 seconds, and no temperature increase was recorded on days 1, 4, or 6. In all the patients, the hair clearance between baseline and the 6th treatment, the 6-month follow-up, and the 12-month follow-up rated as significant P < 0.05. The mean percentage of hair reduction was 97.3% at 12 months. In conclusion, the clinical findings demonstrate the safety and efficacy of the 808 nm diode laser system for intraoral hair removal Lasers Surg. Med. 51:516-521, 2019. © 2019 Wiley Periodicals, Inc.

Infrared Stark and Zeeman spectroscopy of OH-CO: The entrance channel complex along the OH + CO → trans-HOCO reaction pathway.

Sequential capture of OH and CO by superfluid helium droplets leads exclusively to the formation of the linear, entrance-channel complex, OH-CO. This species is characterized by infrared laser Stark and Zeeman spectroscopy via measurements of the fundamental OH stretching vibration. Experimental dipole moments are in disagreement with ab initio calculations at the equilibrium geometry, indicating large-amplitude motion on the ground state potential energy surface. Vibrational averaging along the hydroxyl bending coordinate recovers 80% of the observed deviation from the equilibrium dipole moment. Inhomogeneous line broadening in the zero-field spectrum is modeled with an effective Hamiltonian approach that aims to account for the anisotropic molecule-helium interaction potential that arises as the OH-CO complex is displaced from the center of the droplet.

Two-center three-electron bonding in ClNH3 revealed via helium droplet infrared laser Stark spectroscopy: Entrance channel complex along the Cl + NH3 → ClNH2 + H reaction.

Pyrolytic dissociation of Cl2 is employed to dope helium droplets with single Cl atoms. Sequential addition of NH3 to Cl-doped droplets leads to the formation of a complex residing in the entry valley to the substitution reaction Cl + NH3 → ClNH2 + H. Infrared Stark spectroscopy in the NH stretching region reveals symmetric and antisymmetric vibrations of a C3v symmetric top. Frequency shifts from NH3 and dipole moment measurements are consistent with a ClNH3 complex containing a relatively strong two-center three-electron (2c-3e) bond. The nature of the 2c-3e bonding in ClNH3 is explored computationally and found to be consistent with the complexation-induced blue shifts observed experimentally. Computations of interconversion pathways reveal nearly barrierless routes to the formation of this complex, consistent with the absence in experimental spectra of two other complexes, NH3Cl and Cl-HNH2, which are predicted in the entry valley to the hydrogen abstraction reaction Cl + NH3 → HCl + NH2.

Mid-infrared signatures of hydroxyl containing water clusters: Infrared laser Stark spectroscopy of OH-H2O and OH(D2O)n (n = 1-3).

Small water clusters containing a single hydroxyl radical are synthesized in liquid helium droplets. The OH-H2O and OH(D2O)n clusters (n = 1-3) are probed with infrared laser spectroscopy in the vicinity of the hydroxyl radical OH stretch vibration. Experimental band origins are qualitatively consistent with ab initio calculations of the global minimum structures; however, frequency shifts from isolated OH are significantly over-predicted by both B3LYP and MP2 methods. An effective Hamiltonian that accounts for partial quenching of electronic angular momentum is used to analyze Stark spectra of the OH-H2O and OH-D2O binary complexes, revealing a 3.70(5) D permanent electric dipole moment. Computations of the dipole moment are in good agreement with experiment when large-amplitude vibrational averaging is taken into account. Polarization spectroscopy is employed to characterize two vibrational bands assigned to OH(D2O)2, revealing two nearly isoenergetic cyclic isomers that differ in the orientation of the non-hydrogen-bonded deuterium atoms relative to the plane of the three oxygen atoms. The dipole moments for these clusters are determined to be approximately 2.5 and 1.8 D for "up-up" and "up-down" structures, respectively. Hydroxyl stretching bands of larger clusters containing three or more D2O molecules are observed shifted approximately 300 cm(-1) to the red of the isolated OH radical. Pressure dependence studies and ab initio calculations imply the presence of multiple cyclic isomers of OH(D2O)3.

On the Stark effect in open shell complexes exhibiting partially quenched electronic angular momentum: Infrared laser Stark spectroscopy of OH–C2H2, OH–C2H4, and OH–H2O

The Stark effect is considered for polyatomic open shell complexes that exhibit partially quenched electronic angular momentum. Matrix elements of the Stark Hamiltonian represented in a parity conserving Hund’s case (a) basis are derived for the most general case, in which the permanent dipole moment has projections on all three inertial axes of the system. Transition intensities are derived, again for the most general case, in which the laser polarization has projections onto axes parallel and perpendicular to the Stark electric field, and the transition dipole moment vector is projected onto all three inertial axes in the molecular frame. Simulations derived from this model are compared to experimental rovibrational Stark spectra of OH–C2H2, OH–C2H4, and OH–H2O complexes formed in helium nanodroplets.

Reactive intermediates in (4)He nanodroplets: infrared laser Stark spectroscopy of dihydroxycarbene.

Singlet dihydroxycarbene (HOC̈OH) is produced via pyrolytic decomposition of oxalic acid, captured by helium nanodroplets, and probed with infrared laser Stark spectroscopy. Rovibrational bands in the OH stretch region are assigned to either trans,trans- or trans,cis-rotamers on the basis of symmetry type, nuclear spin statistical weights, and comparisons to electronic structure theory calculations. Stark spectroscopy provides the inertial components of the permanent electric dipole moments for these rotamers. The dipole components for trans, trans- and trans, cis-rotamers are (μa, μb) = (0.00, 0.68(6)) and (1.63(3), 1.50(5)), respectively. The infrared spectra lack evidence for the higher energy cis,cis-rotamer, which is consistent with a previously proposed pyrolytic decomposition mechanism of oxalic acid and computations of HOC̈OH torsional interconversion and tautomerization barriers.

Keldysh theory in a few-cycle laser pulse, inelastic tunneling and Stark shift: comparison with ab initio calculation

Combining the Keldysh theory for a few cycle laser pulse with the theory of the inelastic tunneling (Kornev A S and Zon B A 2012 Phys. Rev. A 85 035402) agrees very well with the ab initio simulations performed by Rohringer and Santra (2009 Phys. Rev. A 79 053402) for the Ne atom. However, for the heavier Xe atom, agreement between analytical and numerical theories is not satisfactory. To eliminate this disagreement, we took into account the Stark shift of atomic level energies. As a result, the agreement between analytical and numerical theories significantly improved, but for Ne, it became worse. We discussed possible causes of these disagreements.

Study of the Q Branch Structure of the 14N and 15N Isotopologues of the ν4 Band of Ammonia Using Frequency Chirped Quantum Cascade Lasers

Intrapulse quantum cascade (QC) laser spectrometers are able to produce both saturation and molecular alignment of a gas sample owing to the rapid sweep of the radiation through the absorption features. In the QC lasers used to study the (14)N and (15)N isotopologues of the ν4 band of ammonia centered near 1625 cm(-1), the variation of the chirp rate during the scan is very large, from ca. 85 to ca. 15 MHz ns(-1). In the rapid chirp zone the collisional interaction time of the laser radiation with the gas molecules is short, and large rapid passage effects are seen, whereas at the slow chirp end the line shape resembles that of a Doppler broadened line. The total scan range of the QC laser of ca. 10 cm(-1) is sufficient to allow the spectra of both isotopologues to be recorded and the rapid and slow interactions with the laser radiation to be seen. The rapid passage effects are enhanced by the use of an off axis Herriott cell with an effective path length of 62 m, which allows a buildup of polarization to occur. The effective resolution of the chirped QC laser is ca. 0.012 cm(-1) full width at half-maximum in the 1625 cm(-1) region. The results of these experiments are compared with those of other studies of the ν4 band of ammonia carried out using Fourier transform and Laser Stark spectroscopy. They also demonstrate the versatility of the down chirped QC laser for investigating collisional effects in low pressure gases using long absorbing path lengths.

Absorption in laser structures with coupled and uncoupled quantum dots in an electric field at room temperature

The absorption of uncoupled and tunnel-coupled vertically correlated quantum dots (QDs), measured at room temperature, has been experimentally compared. It is revealed that matching of the laser wavelength and Stark shift for laser structures with tunnel-coupled QDs leads to resonant absorption with formation of bound and antibound exciton states with a splitting energy of ∼62 meV between them in QD molecules. For these states, an external field causes a large linear Stark shift (up to 68 meV). For uncoupled QDs, one resonant absorption peak with the formation of an exciton (for which the Stark shift does not exceed 13 meV) is observed.

Electric-Field Induced Dipole Blockade with Rydberg Atoms

High resolution laser Stark excitation of np (60<n<85) Rydberg states of ultracold cesium atoms shows an efficient blockade of the excitation attributed to long-range dipole-dipole interaction. The dipole blockade effect is observed as a quenching of the Rydberg excitation depending on the value of the dipole moment induced by the external electric field. Effects of ions which could match the dipole blockade effect are discussed in detail but are ruled out for our experimental conditions. Analytic and Monte Carlo simulations of the excitation of an ensemble of interacting Rydberg atoms agree with the experiments and indicate a major role of the nearest neighboring Rydberg atom.

Far-Infrared Laser Stark Spectroscopy of 1,1 Difluoroethylene

The far-infrared laser Stark spectrum of 1,1 difluoroethylene (H2C=CF2) has been investigated with the 311 μm line of the hydrogen cyanide (HCN) laser. Numerous families of absorption lines have been observed for both parallel and perpendicular polarizations up to 60 000 V/cm. Three families of resonances have been identified as J(Ka,Kc) = 41(35,7) ← 40(33,8), 40(36,5) ← 39(34,6) and 43(35,8) ← 42(33,9). The Stark shift for the first two transitions can be adequately explained by quasi-first-order calculations, whereas the Stark shift for the third transition requires second-order corrections. The zero-field frequencies for these transitions have been experimentally determined and are reported with fractional uncertainties up to a few parts in 106.

Laser spectroscopy of free pentacene molecules (II): Stark effect of the vibrationless S1←S transition

Laser Stark spectroscopy has been performed for the first time on free pentacene molecules seeded in a highly collimated supersonic argon beam. The Stark effect of the vibrationless S1←S0 transition of pentacene at 18 649 cm−1 was investigated in a static homogeneous electric field up to 81 kV/cm. Within the unresolved rotational structure, an unexpected large quadratic Stark effect was observed. An analysis of the shifts of sub-band heads and characteristic structures was performed by simulating the complete Stark spectrum using second-order perturbation theory. Surprisingly large values for the differences of the molecular polarizability between the electronic ground state X 1A1g and the excited A 1B2u state were found: ΔP̄=1/3(ΔPaa+ΔPbb+ΔPcc)=9.1(3)×102 Å3, ΔPcc=Pcc′−Pcc″=13.7(8)×102 Å3, ΔPxx=−1.4(8)×102 Å3, ΔPyy=15.0(7)×102 Å3 (x=a, y=b, or vice versa). Attributing the in-plane axes uniquely and the determination of the ground state anisotropy was not possible. It is assumed that the large polarizability of the excited state is dominated by contributions of low-frequency vibrational levels. Indications for deviation from second-order perturbation theory are observed.

High-resolution ultraviolet laser spectroscopy on jet-cooled benzene molecules: Ground and excited electronic state polarizabilities determined from static Stark effect measurements

Static electric polarizabilities of the S0(1A1g) ground electronic and the vibronically excited 61 S1(1B2u) state of benzene were measured by applying ultraviolet (UV) laser Stark spectroscopy. The experimental setup consisted of a frequency doubled tunable narrow-band continuous wave (cw) laser system operating at 259 nm, a molecular beam apparatus, and a capacitor capable of generating strong static and homogeneous electric fields up to 250 kV/cm. Experimental linewidths of less than 30 MHz were achieved for the rotational transitions, and Stark displacements of typically several 10 MHz could be detected. Stark patterns of 16 rotational lines were recorded and analyzed under different field strengths. Validity of second-order perturbation theory was confirmed by the observed effects, and the diagonal components of the polarizability tensors could be adjusted by a weighted least-squares technique. Results were applied to calculating Stark spectra and comparing them to experimental data. Good agreement could be found, except for an obscure singular perturbation within one rotational line. The new polarizabilities were compared to both experimental and theoretical results in the literature. Ground state data are in general agreement, whereas no comparable experimental work addressing the excited electronic state exists. Finally, polarizabilities of the beginning five polyacenes were compiled and compared with the benzene data.

Laser Stark and Fourier transform spectroscopy and assignment of optically pumped far-infrared laser lines of methanol-D 4

In this work, the Fourier transform far infrared (FTFIR) and infrared (IR) spectra of the completely deuterated methanol species CD 3OD corresponding to the torsion–rotation band in the vibrational ground state and the CO stretch vibrational band, respectively, have been recorded and analyzed. From the IR analysis it has been possible to partially identify optically pumped FIR laser lines for four different CO 2 laser pump systems from analytical considerations. In addition, laser Stark spectra have been studied using the HCN laser lines operating at 311 and 337 μm, in CD 3OD. A number of Q-branch lines for K=11←10 E 2 n=0 assigned earlier and two strong R-branch transitions viz. R(8) and R(10) for K=7←6 A n=0 have been considered. The laser Stark spectrum for the R(10) transition has been reassigned from the previous work. The availability of the zero field frequencies with a precision of ±6 MHz from the high resolution FTFIR spectrum allowed the dipole moment of this important molecular species to be determined for the first time. The results will be useful for accurate intensity calculation and prediction of optically pumped FIR laser lines and astrophysically significant transitions.

Molecular parameters of 13CD 3OD

In a recent letter Jackson et al. [1] have reported the observation of the far-infrared (FIR) laser Stark spectra in 13CD 3OD species of methanol for the first time, corresponding to the Q-branch transition J K = J 5 ← J 4 E 2 in the first excited torsional state ( v t = 1) for the J = 9–15 members, using the HCN laser. The molecular parameters used for the predictions have been obtained from the extrapolation from other molecular species. It is pertinent to note that the predictions were accurate enough to make the assignments straightforward (G.R. Sudhakaran, private communication). With the availability of the zero field frequencies for the Q-branch multiplets, the molecular parameters have been improved. In this letter the molecular parameters for 13CD 3OD are reported for the first time. In addition, comments are also made on the FIR laser lines reported to be pumped in 13CD 3OD with a CO 2 laser.

Far-Infrared Laser Stark Spectroscopy of PH3

The laser Stark spectra of phosphine have been studied using the 195- and 195′-μm lines of the DCN laser. The spectra were taken at room temperature for both parallel and perpendicular polarizations up to 57000 V/cm. The observed resonances have been assigned to the pure rotational transitionsJK= 6K← 5Kin the ν2= 1 vibrational state for bothEandAsymmetries withK= 1 through 5. In addition, the zero-field forbidden transitions,JK= 63← 53A1← A1andA2← A2, have been observed for the first time. The measured zero-field frequencies for all of the observed transitions are in excellent agreement with those calculated from the available molecular constants and represent an increase in accuracy over prior measurements.

The ν2/ν4Diad of PH3

The ν2/ν4diad of phosphine has been investigated between 920 and 1080 cm−1by laser sideband spectroscopy. Using 62 observed lines and more than 250 transitions measured by other authors, including microwave, far infrared, and laser Stark observations, a fit was performed, which achieved a standard deviation of 1.2 MHz.A1/A2splitting due to vibrational rotational interaction could be resolved in ten transitions.

Electric field measurements in discharges by Doppler-free two-photon laser Stark spectroscopy of atomic hydrogen

We show experimentally that the Doppler-free, two-photon excitation of n = 3 states of atomic hydrogen using a tunable, narrow band laser source at 205 nm, can be used to measure the electric field in the sheath of a low pressure glow discharge with good sensitivity (50 V/cm). The observed excitation spectra show a well-resolved Stark structure in good agreement with simulated spectra calculated for different values of the electric field. This method is promising for measuring the electric field magnitude in a number of environments because of the large laser induced fluorescence yield per ground state H atom.

Assignment and frequency measurement of rotational transitions of 13CD 3OH by intracavity laser Stark spectroscopy

We present the results of an intracavity Stark spectroscopy experiment on the fundamental state of 13CD 3OH. We use an optically pumped hybrid waveguide FIR laser, CH 2F 2 as active molecule, and 13CD 3OH as absorbent molecule. No Brewster window is needed to separate the lasing gas from the absorbing deuterated methanol. An absorption line is assigned as E 1 symmetry ( n, K, K): (1,4,18) → (1,5,18) and its frequency is measured as 63.08631 cm −1 with a precision of a few parts in 10 7; two more absorptions are reported and a tentative assignment is given for one of them.