Hyperfine structure measurement of rubidium atom and tunable diode laser stabilization by using Sagnac interferometer

The Rubidium saturated absorption spectra for D2 transition lines are used to measure the Fabry-Perot interferometer free spectral range (FSR). The scale linearity of the laser frequency tuning is determined. The Sagnac interferometer has been used for the laser stabilization. The result shows that the laser frequency is stabilized upto sub-mega Herz level. Also the hyperfine structure [5(2)S(1/2) F = 3 --> F' = 2, 3, 4 5(2)P(3/2) 85Rb] of the rubidium atom has been measured by using the tilt locking method, which shows the same result as the conventional saturation spectroscopy.     

Self-aligned extended-cavity diode laser stabilized by the Zeeman effect on the cesium D2 line

An extended-cavity diode laser at 852 nm has been built especially for the purpose of cooling and probing cesium atoms. It is a compact, self-aligned, and continuously tunable laser source having a 100-kHz linewidth and 60-mW output power. The electronic control of the laser frequency by the piezodriven external reflector covers a 4.5-kHz bandwidth, allowing full compensation of acoustic frequency noise without any adverse effect on the laser intensity noise. We locked this laser to Doppler-free resonances on the cesium D(2) line by using the Zeeman modulation technique, resulting in the frequency and the intensity of the laser beam being unmodulated. We also tuned the locked laser frequency over a span of 120 MHz by using the dc Zeeman effect to shift the F = 4-F' = 5 reference transition.     

Frequency stabilization of a laser diode with use of light-induced birefringence in an atomic vapor

We present a simple modulation-free technique to stabilize a laser frequency to the Doppler-free spectra of an atomic vapor. Polarization spectroscopy with use of a balanced polarimeter allows us to obtain a background-free dispersion signal suitable for high-speed and robust frequency stabilization. We employed the method to the 5S(1/2) F = 2 --> 5P(3/2) F' = 3 transition of 87Rb atoms. The achieved feedback bandwidth was approximately 100 kHz, and an efficient suppression of the frequency noise in a laboratory environment was attained.     

Nonlinear Faraday rotation for optical limitation

The possible use of the nonlinear Faraday effect for optical limitation of the laser power is investigated in a resonant Faraday medium placed between two crossed polarizers. The results are comparable with those obtained at strong magnetic fields as a result of the linear Faraday effect. Advantages of the method are the narrow bandwidth and the wide field of view. The investigations are interesting from the viewpoint of applications for optical sensor protection and automation of the experiment. All measurements are performed at the F(g) = 2 --> F(e) = 1 hyperfine structure transition of the 87Rb D1 line.     

Properties of Nd3+-doped and undoped tetragonal PbWO4, NaY(WO4)2, CaWO4, and undoped monoclinic ZnWO4 and CdWO4 as laser-active and stimulated raman scattering-active crystals

Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.     

Measurement of the Unperturbed Hydrogen Hyperfine Transition Frequency

The results of a joint experiment aimed primarily at the determination of the frequency of the H1 hyperfine transition (F = 1, mF = 0) ? (F = 0, mF = 0) is reported. In terms of the frequency of the Cs133 hyperfine transition (F = 4, mF = 0) ?(F = 3, mF = 0), defined as 9192 631 770 Hz, for the unperturbed hydrogen transition frequency the value ?H = 1420 405 751.768 Hz is obtained. This result is the mean of two independent evaluations against the same cesium reference, which differ by 2 × 10-3 Hz. We estimate the one-sigma uncertainty of the value ?H also to be 2 × 10-3 Hz. One evaluation is based on wall-shift experiments at Harvard University; the other is a result of a new wall-shift measurement using many storage bulbs of different sizes at the National Bureau of Standards. The experimental procedures and the applied corrections are described. Results for the wall shift and for the frequency of hydrogen are compared with previously published values, and error limits of the experiments are discussed.     

Nonlinear plasmonics at planar metal surfaces

We investigate the nonlinear optical response of a noble metal surface. We derive the components of the third-order nonlinear susceptibility and determine an absolute value of χ((3))≈0.2 nm(2) V(-2), a value that is more than two orders of magnitude larger than the values found for typical nonlinear laser crystals. Using nonlinear four-wave mixing (4WM) with incident laser pulses of frequencies ω(1) and ω(2), we generate fields oscillating at the nonlinear frequency ω(4WM)=2ω(1)-ω(2). We identify and discuss three distinct regimes: (i) a regime where the 4WM field is propagating, (ii) a regime where it is evanescent, and (iii) a regime where the nonlinear response couples to surface plasmon polaritons.     

Low-frequency wavelength modulation spectroscopy with D2 transition of atomic cesium by use of an external-cavity diode laser

Low-frequency wavelength modulation spectroscopy is acquired with an external-cavity diode laser. The wavelength modulation is achieved with voltage tuning by means of scanning with the piezoelectric stepper motor, which rotates the end mirror in the laser cavity. With optimum 1-kHz frequency modulation and harmonic detection, direct absorption experiments for the 6S(1/2)(F = 4) --> 6P(3/2) transition of the cesium D(2) line were carried out. We found that 6f-harmonic detection is best here with a signal-to-noise voltage ratio of 460.     

超声微泡造影剂的低频动力学行为

低频超声联合微泡造影剂有可能用于治疗肿瘤,因此开展造影剂低频的动力学特性研究是十分重要的。将低频声场(26.2kHz)中有壳和无壳的微泡造影剂视为以流体为负载的非线性振子,由带耗散函数的拉格朗日方程导出在不可压缩的粘滞流体中造影剂球对称振动的运动方程,利用球谐振腔和Mie散射技术对CO2微泡和带人白蛋白壳的全氟丙烷造影剂微泡进行了气泡散射光强I(t)曲线的实验测定,结果与数值模拟曲线相一致。表明:有壳和无壳的造影剂微泡在低频稳态空化时同样呈现大幅膨胀、迅速塌缩和回弹的非线性振荡;如处于内径较小的微血管中,微泡周期性大幅度(>血管内径)膨胀收缩将会引起血管轴向破裂,形成微血管栓塞;而在塌缩相,微泡内的气体被急剧压缩,泡内压强急剧增大,易在泡壁不稳定处形成高速微射流,诱发内皮细胞损伤而形成血栓。     

Absolute Frequency Stabilization of the 3.39-?m Laser on a CH4 Line

Theoretical and experimental studies on a primary standard of wavelength and frequency in the infrared are reported. The 3.39-?m He-Ne laser is tuned to the center of the absorption line of methane which is assigned to the F1(2)) component of the P(7) branch of the ?3 band. The absence of Stark and Zeeman effects under the highest fields tested, the strong absorption at 63.2° K as well as at 78°K, and the separation from other lines are excellent features for a high degree of absolute stability and reproducibility. A method of automatic frequency control of the He-Ne laser at the line-center of methane is described.     

Microwave spectrum asymmetry in an optically pumped cesium beamresonator

This paper deals with a theoretical and experimental study that describes the effect of a frequency detuning of the laser used to achieve optical pumping in a small optically pumped cesium beam resonator. The ground state Zeeman sublevels with opposite angular momentum are unequally populated, leading to an asymmetrical microwave spectrum. The relative population asymmetry as a function of the laser frequency has a dispersion-like shape. Its dependence on laser intensity, applied magnetic field, and laser linewidth is demonstrated for a laser at 852 nm and tuned to the ²S_1/2F=3→²P_3/2F'=3 transition of the Cs D₂ line. Finally, the effect of a slight laser detuning on the Rabi pulling frequency shift is discussed     

High-power cw 671 nm output by intracavity frequency doubling of a double-end-pumped Nd:YVO4 laser

We report on a high-power (cw) red laser at 671 nm by intracavity frequency doubling of a double-end-pumped 1342 nm Nd:YVO4 laser based on the nonlinear crystal LiB3O5. A red output power of 3.38 W is obtained for a pump power of 27 W, with corresponding optical-to-optical efficiency of 12.5%. The 671 nm beam is nearly diffraction limited.     

Generation of deep ultraviolet narrow linewidth laser by mixing frequency Ti:sapphire laser at 5 kHz repetition rate

We demonstrate a scheme to generate deep ultraviolet source by the single-stage high-power Ti:sapphire laser with linewidth of 0.05 nm cryogenically operating at repetition rate of 5 kHz. The fundamental laser was tuned by an intracavity birefringent filter and three etalons with an output power greater than 8 W, corresponding to about 17% optical efficiency. The pulse width was 112 ns and M2<1.1. By using the nonlinear crystals BiB3O6 and KBe2BO3F2, the output power of 2.2 W at second harmonic and 8.5 mW at fourth harmonic laser of about 195 nm were produced. This compact high-repetition rate laser with narrow linewidth would be a promising tunable source for spectroscopy.     

Studies of third-order optical nonlinearities and optical limiting of 2, 3-butanedione dihydrazone

2, 3-butanedione dihydrazone (BDDH) synthesized via chemical route and nonlinear optical parameters, such as nonlinear refractive index (n2), nonlinear absorption coefficient (β), third-order nonlinear optical susceptibility (χ(3)), second hyperpolarizability (γ), and optical-limiting behavior were investigated by single beam z-scan technique for different concentrations. Synthesized sample were irradiated by a Q-switched, frequency doubled Nd:YAG laser and found that n2 and β increases linearly with increasing concentration and hence γ decreases linearly. The excited-state absorption cross sections of BDDH were found to be larger than ground-state absorption cross sections, and it leads to reverse saturable absorption (RSA). The experimental results are well in agreement with the theory and also establish BDDH as one of the potential candidate materials for optical limiting at 532 nm.     

Light and Buffer-Gas Frequency Shifts in the 85Rb-Maser Frequency Standard

Recently we reported the operation of an optically pumped 85Rb maser oscillating at 3.035734 GHz on the field-independent transition 52S1/2(F = 3, mF = 0 ? F = 2, mF = 0) [1]. Apart from cavity pulling, the two major sources of frequency shifts are those due to the buffer gas and the pumping light. The short-term phase stability of the standard is not appreciably affected by these shifts. The buffer-gas shift can be used to advantage to select an output frequency that is different from the ground-state hyperfine frequency.     

Direct observation of transient fluorine atoms with 25-µm wavelength-stabilized diode laser absorption

Through the use of continuous diode laser absorption, detection of transient fluorine atoms with an initial number density in the range of 10(14) cm(-3) has been demonstrated. A crucial part of the continuous-detection technique was laser frequency stabilization with a reference cell of atomic fluorine with Zeeman modulation of the absorption lines to generate a feedback signal. Long-term wavelength stability was demonstrated with second-harmonic phase-sensitive detection of the second-derivative signal for periods up to several hours. For determination of the short-term wavelength stability in the range of microseconds to seconds, a transient signal was generated by photolysis of F(2) with an excimer laser at 308 nm. The initial diode laser absorption was compared to a calculated value obtained from the measured excimer laser fluence, the known dissociation cross section of F(2), and the atomic fluorine absorption cross section, which included a statistical population distribution, the finite bandwidth of the laser dode, and the effects of pressure broadening. The observed absorption was approximately 33% less than the calculated value, possibly because of the diode laser's wavelength instability on the time scale of a few seconds, which is consistent with an observed amplitude instability from pulse to pulse when pulsed at 1-10 Hz.     

Dependence of birefringence and residual stress near laser-induced cracks in fused silica on laser fluence and on laser-pulse number

Measurements of birefringence induced in fused-silica specimens by a crack produced by a 351-nm/500-ps Nd:glass laser as a function of laser fluence F(L) and of number of laser shots N are presented. The varying dimensional parameter is found to be the crack depth a and can be put in the form a(mm) = (0.0096 ? 0.0021)N[(F(L)/F(exit/th)) - 1](2/3) with F(L) >/= F(exit/th)(F(exit/th) is the exit-surface damage threshold). The retardance data are converted into units of stress, thus permitting the estimation of residual stress near the crack. The results of the measured residual stress can be cast in the form varsigma(r)(MPa) approximately (. ? .)[(F(L)/F(exit/th)) - 1](1/2) N(2/3) with F(L)>/= F(exit/th). A theoretical model giving the stress field around a crack is developed for comparison and shows reasonable agreement with the experiment. Good agreement with experimental data of others is also obtained. The effect of residual stresses on fracture strength is pointed out. The results obtained show that the presence of birefringence/residual stress in a fused-silica specimen with a crack on its surface has a strong effect on fracture and should be taken into account in any formulation that involves the failure strength of optical components used in inertial-confinement-fusion experiments.     

Femtosecond Z-scan investigation of nonlinear refraction in surface modified PbS nanoparticles

The third-order optical nonlinearities of surface modified PbS nanoparticles have been measured using the Z-scan technique with femtosecond laser pulses at 780 nm wavelength. The samples studied are the nanoparticles in microemulsion with the PbS concentration ranging from 0.3×10⁻³ to 1.9×10⁻³ M (mol/l). A Z-scan analysis method based on the Huygens–Fresnel (H–F) propagation integral is employed to extract the nonlinear refractive index from the experimental Z-scan data with a large nonlinear phase shift. The nonlinear refractive index of the PbS nanoparticles in microemulsion is found to increase linearly with the PbS concentration. The highest concentration microemulsion gives a nonlinear refractive index of −4.7×10⁻¹² cm²/W, which is approximately 3 orders of magnitude higher than those of commercially available bulk semiconductors, such as ZnS and CdS. In addition, nonlinear absorption in these samples remained unmeasurable up to 0.9 GW/cm². The mechanisms responsible for the observed large refractive nonlinearity are discussed.     

GaN thin films deposited by pulsed laser ablation in nitrogen and ammonia reactive atmospheres

Well-oriented, crystalline GaN films were grown on (11

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0) sapphire substrates in reactive atmospheres of N₂ and NH₃ by pulsed laser deposition. GaN targets were ablated at 2.8 J cm⁻² and the substrate temperature was varied from 500 to 700°C. The background gas pressure was varied from 0.04 to 0.3 mbar. All the films had a wurtzite structure. The crystal quality and preferential orientation depended on the substrate temperature, laser fluence and the presence of the nitriding atmosphere. For both N₂ and NH₃, the most resistive films were preferentially orientated in the [000l] direction. For 700°C the film resistivity was found to increase from 10⁻³ Ω cm when deposited in NH₃ to 10² Ω cm when deposited in N₂. The band-gap, obtained from optical transmission measurements shifted from 3.1 to 3.4 eV. Violet photoluminescence was found in all samples and was centered at 3.2 eV with a full width at half maximum of 0.2 eV. A broad peak in the yellow, centered at 2.1 eV, was detected for films grown in vacuum and ammonia.     

Frequency measurement of the 2S-12D transitions in hydrogen anddeuterium, new determination of the Rydberg constant

We have performed the first pure frequency measurement of the 2S-12D two-photon transitions in atomic hydrogen and deuterium. These frequencies are compared to two optical standards, the CO₂ laser stabilized on the OsO₄ molecule and the optical rubidium laser standard (LD/Rb) (namely, a laser diode at 778 nm stabilized on the 5S_1/2-5D_5/2 two-photon transition of rubidium). The main part of the experiment is located in the Laboratoire Kastler-Brossel (LKB), one part of the frequency chain is in the Laboratoire Primaire du Temps et des Frequences (LPTF), and two 3 km long optical fibers link the two parts of this experiment. The new value of the Rydberg constant is R_∞=109 737.315 686 06 (79) cm^-1