Infrared laser-spectroscopic analysis of <Superscript>14</Superscript>NO and <Superscript>15</Superscript>NO in human breath

We report on monitoring of nitric oxide (NO) traces in human breath via infrared cavity leak-out spectroscopy. Using a CO sideband laser near 5 μm wavelength and an optical cavity with two high-reflectivity mirrors (R=99.98%), the minimum detectable absorption is 2×10⁻¹⁰ cm⁻¹ Hz^1/2. This allows for spectroscopic analysis of rare NO isotopologues with unprecedented sensitivity. Application to simultaneous online detection of ¹⁴NO and ¹⁵NO in breath samples collected in the nasal cavity is described for the first time. We achieved a noise-equivalent detection limit of 7 parts per trillion for nasal ¹⁵NO (integration time: 70 s).     

A 750-mW,continuous-wave,solid-state laser source at 313 nm for cooling and manipulating trapped <Superscript>9</Superscript>Be<Superscript>+</Superscript> ions

We present a solid-state laser system that generates 750 mW of continuous-wave, single-frequency output at 313 nm. Sum-frequency generation with fiber lasers at 1550 and 1051 nm produces up to 2 W at 626 nm. This visible light is then converted to ultraviolet by cavity-enhanced second-harmonic generation. The laser output can be tuned over a 495-GHz range, which includes the ⁹Be⁺ laser cooling and repumping transitions. This is the first report of a narrow-linewidth laser system with sufficient power to perform fault-tolerant quantum-gate operations with trapped ⁹Be⁺ ions by use of stimulated Raman transitions.     

Development of multiple laser frequency control system for Ca<Superscript>+</Superscript> isotope ion cooling

We here developed and evaluated a laser frequency control system which synchronizes the laser frequency to the resonance of target Ca ⁺ isotope ion whose having more than 8 GHz of isotope shift based on the Fringe Offset Lock method for simple operation of ICPMS-ILECS (Inductively Coupled Plasma Mass Spectrometry - Ion trap Laser Cooling Spectroscopy) The system fulfilled the minimum requirements of four slave lasers stability for Doppler cooling of Ca ⁺ ions. A performance of the system was evaluated by cooling ⁴⁰Ca ⁺ ions with the stabilized slave lasers. All the stable even Ca ⁺ isotope ions were trapped and their fluorescence was observed by switching laser frequencies using the system. An odd calcium isotope ⁴³Ca ⁺cooling was also succeeded by the control system.     

A miniature tunable TEA CO<Subscript>2</Subscript> laser using isotope <Superscript>13</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript> and <Superscript>12</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript>

A miniature tunable TEA CO₂ laser using isotope ¹³C¹⁶O₂ as the active medium is developed to extend the spectral range of CO₂ lasers for further application. The optimization of the energy parameters of the tunable TEA ¹³C¹⁶O₂ laser and the same laser using ¹²C¹⁶O₂ are studied. When a gas mixture (¹³C¹⁶O₂: N₂: He = 1: 1: 3) at a total pressure of 6.4 × 10⁴ Pa is used, the TEA ¹³C¹⁶O₂ laser of a 45-cm³ active volume obtains 51 emission lines in the [00⁰1–10⁰0] and [00⁰1–02⁰0] bands. The maximum pulse energy of the TEA ¹³C¹⁶O₂ laser is about 357 mJ. The same laser using the conventional gas mixture (¹²C¹⁶O₂: N₂: He = 1: 1: 3) at a pressure of 6.66 × 10⁴ Pa is measured to obtain 69 laser emission lines and the maximum pulse energy of laser radiation is about 409 mJ.     

Spectroscopic indications of the possible optical cooling effect in fluoride crystals activated by Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

The results of spectral kinetic studies of several fluoride crystals activated by Yb³⁺ and Tm³⁺ ions are presented, and their possible application as cooling elements of optical refrigerators is discussed. Optimum excitation conditions for the laser cooling effect in these crystals are found. The cooling efficiency is established to depend on the degree of order in the active medium.     

Development of an apparatus for cooling <Superscript>6</Superscript>Li-<Superscript>87</Superscript>Rb Fermi-Bose mixtures in a light-assisted magnetic trap

We describe an experimental setup designed to produce ultracold trapped gas clouds of fermionic ⁶Li and bosonic ⁸⁷Rb. This combination of alkali metals has the potential to reach deeper Fermi degeneracy with respect to other mixtures since it allows for improved heat capacity matching which optimizes sympathetic cooling efficiency. Atomic beams of the two species are independently produced and then decelerated by Zeeman slowers. The slowed atoms are collected into a magneto-optical trap and then transferred into a quadrupole magnetic trap. An ultracold Fermi gas with temperature in the 10^?3 T _F range should be attainable through selective confinement of the two species via a properly detuned laser beam focused in the center of the magnetic trap.     

Wavelength tunable linear cavity cladding pump Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>co-doped fiber laser operating in L-band

We have demonstrated a novel tunable linear cavity Er³⁺/Yb³⁺ co-doped fiber laser, which utilizes amplified spontaneous emission as a secondary pump source so that it can operate in L-band. The tuning wavelength range can be up to 34 nm, from 1588.6 to 1622.6 nm, and the output power excursion of the laser at different wavelengths can be less than 0.4 dB by using a two sections of high-birefringence fiber loop mirror as the wavelength filter. The high output power of 200 mW is realized by using the cladding-pump.     

Zeeman laser cooling of <Superscript>85</Superscript>Rb atoms in transverse magnetic field

The process of Zeeman laser cooling of ⁸⁵Rb atoms in a new scheme employing a transverse magnetic field has been experimentally studied. Upon cooling, the average velocity of atoms was 12 m/s at a beam intensity of 7.2×10¹² s^?1 and an atomic density of 4.7×10¹⁰ cm^?3.     

Observation of sympathetically cooled <Superscript>43</Superscript>Ca<Superscript>+</Superscript> ions in a linear ion trap

We report the observation of sympathetically cooled ⁴³Ca⁺ (natural abundance 0.135%) in a linear ion trap utilizing simultaneously trapped isotope ions as coolant. We investigated different possibilities of realizing efficient sympathetic cooling and observed the peaks of the hyperfine transitions of ⁴³Ca⁺ under various experimental conditions.     

Kinetics of Rb<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and Rb<Superscript>+</Superscript> formation in laser-excited rubidium vapor

We have studied the formation of the molecular ion Rb₂⁺ and the atomic ion Rb⁺. These are created in laser excited rubidium vapor at the first resonance, 5s–5p and 5p-nl transitions. A theoretical model is applied to this interaction to explain the time evolution and the laser-power dependence of the population density of Rb⁺ and Rb₂⁺. A set of rate equations which describe: the temporal variation of the population density of the excited states; the atomic ion density; and the electron density, were solved numerically under the experimental conditions of Barbier and Cheret. In their experiment the Rb concentration was 1×10¹³cm⁻³ and the laser power was taken to be 50–500 mW at vapor temperature = 450 K. The results showed that the main processes for producing Rb₂⁺ are associative ionization and Hornbeck-Molnar ionization. The calculations have also showed that, the atomic ions Rb⁺ are formed through the Penning Ionization (PI) and photoionization processes. Moreover, a reasonable agreement between the experimental results and our calculations for the ion currents of the Rb⁺ and Rb₂⁺ is obtained.      

Experimental search for laser-induced effects in <Superscript>151</Superscript>Eu and <Superscript>57</Superscript>Fe doped crystals

We studied the Mössbauer effect in ¹⁵¹Eu and ⁵⁷Fe doped crystals in the search for laser-induced effects caused by changes in the hyperfine interaction due to electronic excitation. The Mössbauer spectra observed in the presence of laser radiation demonstrated a notable change of the shape of the ¹⁵¹Eu spectrum and the appearance of an additional hyperfine pattern in the case of the ⁵⁷Fe Mössbauer resonance.     

Loading rate of Yb<Superscript>+</Superscript> loaded through photoionization in radiofrequency ion trap

We investigate the loading rate of Yb⁺ ions loaded through photoionization in a radiofrequency trap. The absolute or relative number of the loaded trapped ions is measured by use of an electric resonance of the secular motion. This method is applicable even in the presence of anharmonicity. In two-color photoionization, where the first-excitation laser drives the ¹S₀–¹P₁ transition in the Yb atom and the second one ionizes the atom from the ¹P₁ state, the loading rate is at its highest by the excitation of the ionization potential. A similar loading rate is observed at the second-laser wavelength around 369.5 nm, which is the wavelength for the cooling transition of Yb⁺. We estimate the loading cross section to be 40(15) Mb for the two-color excitation of the ionization potential. The excitation of the Yb atoms in the Rydberg states is detected by the enhancement of the loading rate. By irradiation with only the first-excitation laser, Yb⁺ is produced at a rate three orders of magnitude smaller than that when the non-resonant two-photon absorption from the ¹P₁ state is the dominant process. We also measure the charge-exchange rate between Yb⁺ and Yb, and discuss its effect on isotope-selective photoionization loading.     

Photodesorption of O<Subscript>2</Subscript> from Ag<Subscript>2</Subscript><Superscript>-</Superscript>: A time-resolved study of Ag<Subscript>2</Subscript>O<Subscript>2</Subscript><Superscript>-</Superscript>

We present time-resolved photoelectron spectra of mass-selected Ag₂O₂ anions. The anions are photoexcited by photons with an energy of 3.1 eV, and photoelectron spectra of the excited species Ag₂O₂ ^{- *} and the subsequently appearing fragments are recorded using a probe laser pulse with a photon energy of 1.5 eV. The excited state of Ag₂O₂ ^- has a short lifetime of 130 fs±70 fs only and decays by direct photodesorption of O₂. The data demonstrate the ability of time-resolved photoelectron spectroscopy (TR-PES) to observe the breaking of chemical bonds if the decay process of the excited state is direct (non-thermal desorption). The data are compared to recent results of a NeNePo experiment [1] on the same system. PACS 68.43.Tj; 78.47.+p; 33.80.Eh; 36.40.-c     

Studying the possibility of deep laser cooling of <Superscript>24</Superscript>Mg atoms in an optical lattice: Two-level quantum model

The possible deep laser cooling of ²⁴Mg atoms in a deep optical lattice in the presence of an additional pumping field resonant to the narrow 3s3s¹S₀ → 3s3p³P₁ (λ = 457 nm) optical transition is studied. Two quantum models of the laser cooling of atoms in the optical trap are compared. One is based on the direct numerical solution to the kinetic quantum equation for an atomic density matrix; it considers both optical pumping and quantum recoil effects during interaction between the atoms and field photons. The second, simplified model is based on decomposing the states of the atoms over the levels of vibration in the optical trap and analyzing the evolution of these states. The comparison allows derivation of optical field parameters (pumping field intensity and detuning) that ensure cooling of the atoms to minimal energies. The conditions for fast laser cooling in an optical trap are found.     

Frequency measurements in the b <Superscript>3</Superscript>Π(0<Subscript>u</Subscript><Superscript>+</Superscript>) - X <Superscript>1</Superscript>Σ<Subscript>g</Subscript><Superscript>+</Superscript> system of K<Subscript>2</Subscript>

Absolute transition frequencies of the b ³Π(0_u ⁺) - X ¹Σ_g ⁺ system of K₂ were measured in a molecular beam with Lamb dip absorption spectroscopy applying a frequency comb from a femtosecond pulsed laser. Both, K atoms and K₂ molecules are present in the beam and are expected to interact by collisions. The atoms can be deflected optically out of the beam, and thus the collision rate between K atoms and K₂ molecules is changed by about an order of magnitude. The molecular transition frequencies for low collisional rate are compared with those for high one. Limits for the collisional frequency shift within the beam are determined.     

Line shape parameters study of the 6p7p (<Superscript>1</Superscript>P<Subscript>1</Subscript>, <Superscript>3</Superscript>D<Subscript>1</Subscript> and <Superscript>3</Superscript>P<Subscript>1</Subscript>): Autoionizing resonances in barium

We report a systematic line shape analysis study of the 6p7p configuration based ¹P₁, ³D₁ and ³P₁ autoionizing resonances in barium using a Nd:YAG pumped dye laser system in conjunction with a thermionic diode ion detector. The even parity isolated autoionizing resonances have been approached via four intermediate states 6 snp ¹P₁ (6 ≤n ≤8) and 5d6p ¹P₁. A comparison of the Fano parameters of the resonance profiles reveals that the width of an autoionizing resonance is independent of the excitation path while the line profile parameter changes with the selection of different intermediate states.     

Compact all-solid-state continuous-wave single-frequency UV source with frequency stabilization for laser cooling of Be<Superscript>+</Superscript> ions

A compact setup for generation, frequency stabilization, and precision tuning of UV laser radiation at 313 nm was developed. The source is based on frequency quintupling of a C-band telecom laser at 1565 nm, amplified in a fiber amplifier. The maximum output power of the source at 313 nm is 100 mW. An additional feature of the source is the high-power output at the fundamental and the intermediate second- and third-harmonic wavelengths. The source was tested by demonstration of laser cooling of Be⁺ ions in an ion-trap apparatus. The output of the source at the third-harmonic wavelength (522 nm) was used for stabilization of the laser frequency to molecular iodine transitions. Sub-Doppler spectroscopy and frequency measurements of hyperfine transitions in molecular iodine were carried out in the range relevant for the Be⁺ laser cooling application.     

An efficient pathway for Li<Superscript>6</Superscript> isotope enrichment

Separation of lithium isotopes has been achieved using two-step laser photoionization in conjunction with an atomic beam and in-house built time of flight (TOF) mass spectrometer. We present an efficient pathway for the enrichment of Li⁶ isotope by tuning the exciter laser to the 3p ² P _{1/2, 3/2} excited state of Li⁶. A concentration of up to 60% is demonstrated from a natural isotopic abundant lithium sample. In addition, the first measurement of the absolute photoionization cross-section of the 3p excited state of Li⁶ and Li⁷ are reported as 26.8±4 Mb and 25.5±3.8 Mb, respectively. PACS 32.10.Bi; 32.80.t; 32.80.Fb     

Effects of the internuclear vector on the photoelectron angular distributions of H<Subscript>2</Subscript><Superscript>+</Superscript>

We study the photoelectron angular distributions (PADs) of diatomic molecule H₂ ⁺ irradiated by intense laser fields using a nonperturbative scattering theory. We find that the internuclear vector may change the PADs. The PADs have qualitative changes with the increasing of the internuclear distance. The molecular orientation affect the symmetry of the PADs. When the internuclear vector is vertical or parallel to the laser polarization vector, the PADs are four-fold symmetric; for other case the PADs are two-fold symmetric. Due to the modulation effect resulting from the molecular multi-core nature, the size of the jet and the main lobe can be enlarged or reduced. The molecular modulation effect become obvious for large internuclear distance.     

Measurement of the <Superscript>13</Superscript>CO<Subscript>2</Subscript>/<Superscript>12</Superscript>CO<Subscript>2</Subscript> concentration ratio in exhaled air by diode laser spectroscopy

A method for determining the relative concentration of ¹³C/₁₂C isotopes by the vibrational-rotational spectrum of CO₂ molecule absorption in the range near 2 μm was proposed. The use of the entire region of the diode laser tuning (∼7 cm⁻¹) and multivariate linear regression for spectrum approximation allow measurements at atmospheric pressure. The laser frequency is additionally stabilized by injection current variation. The ultimate sensitivity of the setup, determined by the plot of the squared Alan variance, is 0.03% for 2-min signal acquisition. The system does not contain elements cooled by liquid nitrogen and can be used in medical diagnostics.