Femtosecond fiber laser based methane optical clock

An optical clock based on an Er³⁺ fiber femtosecond laser and a two-mode He–Ne/CH₄ optical frequency standard (λ=3.39 μm) is realized. Difference-frequency generation is used to down convert the 1.5-μm frequency comb of the Er³⁺ femtosecond laser to the 3.4-μm range. The generated infrared comb overlaps with the He–Ne/CH₄ laser wavelength and does not depend on the carrier–envelope offset frequency of the 1.5-μm comb. In this way a direct phase-coherent connection between the optical frequency of the He–Ne/CH₄ standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock is measured against a commercial hydrogen maser. The measured relative instability is 1×10⁻¹² at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift of the He–Ne/CH₄ optical standard is dominant.     

Narrow resonances in radiation spectrum of the He-Ne laser with methane absorber

A new phenomenon, a resonance in the radiation spectrum of a gas laser with a nonlinear absorber, is reported for the first time. Frequency stabilization of the He−Ne laser with a methane cell was made by use of the new type of resonance.     

Characterization of probe lasers for thin-film optical measurements

The peak-power-density stability and beam-wander precision of a probe laser are important factors affecting the inspection results in precise thin-film optical measurements. These factors are also key to evaluating a probe laser for in-line long-time operation of precise thin-film optical measurements. The peak-power density and beam wander of liner helium–neon (He–Ne) lasers, random He–Ne lasers, and diode lasers as functions of time are investigated experimentally using a beam profiler. It is found that the linear polarized He–Ne laser is considered to be a promising candidate for a probe laser employed in precise thin-film optical measurements due to better peak-power-density stability and beam-wander precision. Both the peak-power-density stability and beam-wander precision of He–Ne lasers are usually better than that of diode lasers, but an adequate warm-up of He–Ne laser for 30 min is required before thin-film optical measurements are made. After 12 h operation, the linear polarized He–Ne laser is suitable for precise thin-film optical measurements because both the peak-power-density stability and the beam-wander precision reach the minimum level. A cost-effective system composed of two linear polarized He–Ne lasers for long-term operation is proposed. This system can operate for around 0.5–1.2 years in precise thin-film optical measurements under the normal operating life of a He–Ne laser by switching the probe laser every 18 h.     

Spin-flip Raman laser

The properties of the spin-flip Raman laser (SFR laser) which depend on stimulated Raman scattering from mobile conduction electrons in InSb under an external magnetic field are presented. The essential parameters are derived from a macroscopic treatment of the stimulated Raman effect and the microscopic theory of the scattering cross-section, and are compared with experimental results. Output pulse powers as large as 1 kW have been measured for 10.6 and 5.3 μm excitation radiation and continuous powers of 1 W for continuous excitation with a 5.3 μm pump source. The SFR laser offers some interesting applications in physics and chemistry, since its frequency is proportional to the applied magnetic field and its linewidth can be made smaller than 1 kHz.     

Development of an optical time scale

A time standard based on the use of an optical oscillation period of a frequencystable He–Ne laser as a time scale is first described. We obtained highly frequency-stable oscillations in the SHF range that were locked to the oscillations of a He–Ne laser stabilized to an absorption resonance in methane at 3.39 m. A direct comparison of frequency stabilities of a rubidium standard and He–Ne/CH₄ laser has been made. The absolute measurement of the frequency of the He–Ne/CH₄ laser we performed gave a new value of frequency.This work was reported at the 3rd Frequency Standards and Metrology Symposium     

Accurate isotope shift measurements on short lived neon isotopes

We report on fast beam collinear laser spectroscopy measurements that demonstrate the feasibility of accurate isotope shift measurements for short lived Ne isotopes including the proton halo candidate ¹⁷Ne. Ultra high sensitivity is achieved by the application of an efficient resonance detection scheme based on collisional ionization and ion counting via the β decay. A direct measurement of the kinetic energy of the atomic Ne beam provides the required high accuracy. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Raman laser system for multi-wavelength satellite laser ranging

~~A Raman laser system for multi-wavelength satellite laser ranging@K.Hamal$Czech Technical University in Prague,Czech @I.Prochazka$Czech Technical University in Prague,Czech @J.Blazej$Czech Technical University in Prague,Czech1. Yang Fumin, Chen Wanzhen, Zhang Zhongping et al., Satellite laser ranging experiment with sub-centimeter single-shot ranging precision at Shanghai Observatory, Science in China, Ser. A, 2002, 32(10): 935-939. 2. Degnan, J. J., Millimeter accurac…     

Stimulated rotational Raman scattering at multiwavelength under tea CO2 laser pumping with a multiple-pass cell

Stimulated rotational Raman scattering (SRRS) at multiwavelength pumped by TEA CO₂ laser was demonstrated in this paper. Raman mediums were cooled by liquid-N₂ and a multiple-pass cell (MPC) with 25 passes was designed and used. When the para-H2 was pumped by single-longitudinal-mode (SLM) circular polarized TEA CO₂ laser on 10P(20), 9P(20), and 10R(20), 50 mJ 16.95 μm, 350 mJ 14.44 μm, and 536 mJ 16.9 μm radiations were obtained, corresponding to energy conversion efficiency of 1.2, 11.7, and 13.4%, respectively. When the ortho-D₂ was pumped by CO₂ laser on 10R(18), 108 mJ 12.57 μm Raman laser was obtained with energy conversion efficiency of 2.9%.     

Biostimulation of HeLa cells by low-intensity visible light

Summary The action of low-intensity red light with λ=633 nm (a He−Ne laser, a filament lamp with light filters a dye-laser pumped by a Cu laser) on the intensity of nucleic-acid synthesis in HeLa cells 1.5 hours after irradiation has been studied. It has been shown that the DNA synthesis is stimulated similarly after irradiation both by the He−Ne laser and by an ordinary source. The RNA synthesis intensity does not alter in both cases. A high-repetition-rate radiation at λ=633 nm acts in the opposite manner: it stimulates the RNA synthesis and the DNA synthesis remains constant. The action spectra of the DNA and RNA synthesis stimulation by continuous light in the range (570÷693) nm are presented.

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Riassunto è stata studiata l'azione della luce rossa a bassa intensità con λ=633nm (un laser a He−Ne, una lampadina a filamento con filtri per la luce, un laser a colorante pompato da un laser a Cu) sull'intensità della sintesi degli acidi nucleici in cellule HeLa un'ora e mezzo dopo irradiazione. Si è mostrato che la sintesi del DNA è stimolata in modo simile dopo irradiazione sia con laser a He−Ne che da una sorgente ordinaria. La sintesi del RNA non è alterata in entrambi i casi. Una radiazione ad alta frequenza di ripetizione a λ=633 nm agisce in maniera opposta: stimola la sintesi del RNA, mentre la sintesi del DNA resta costante. Si forniscono gli spettri d'azione della sintesi di DNA ed RNA mediante luce continua nell'intervallo da 570 a 693 nm.

     

类氖-锗电子碰撞激发X光激光的增益特性

 电子碰撞激发X光激光的增益特性依赖于电子密度Ne、电子温度Te、增益区宽度D R和介质速度梯度dv/dz等四个表征等离子体内部状态的参数。以类氖-锗离子为例研究了反转和增益特性对Te、Ne的依赖关系，并在典型的增益区宽度（D R=100 μm）和介质速度梯度（dv/dz=1.3×10⁹s^-1）下讨论了共振线俘获对增益特性影响，给出波长为19.6nm, 23.2nm和23.6nm三条激光线的增益目标区域。还讨论了双电子复合过程对离子布居的重要影响。     

Stimulated raman scattering of rapidly amplified short laser pulses

The theory of transient forward stimulated Raman scattering (FSRS) of rapidly amplified short laser pulses is put forth to complement the classical theory for FSRS of stationary pulses. Quantitative conditions for FSRS suppression are identified. In particular, it is shown quantitatively how the limitation imposed by pumped pulse FSRS on the output laser intensity in plasma-based ultrapowerful backward Raman amplifiers can be overcome through a selective detuning of the Stokes resonance.     

Photon-induced switching and tunneling phenomena in a YBCO thin film junction

In the persistent photoconductivity (PPC) phenomenon, illumination of a YBa₂Cu₃O_6.5 thin film junction with a 1mW He−Ne laser leads to the decrease of the critical voltage (similar to the threshold voltage). The decrease of the critical voltage was reversed by illumination with incandescent light. The critical voltage across the junction was experimentally decreased and increased by alternating illumination between He−Ne laser and incandescent light. We also observed visible quenching of the photo-induced state using a 5mW He−Ne laser. Finally, the threshold behavior of the junction was destroyed by illuminating it with incandescent light.     

An application of Pb(Zr,Ti)O3 Ceramic to opto-electronic devices

A lead-zirconate-titanate ceramic is used in an electrically controllable diffraction (ECD) grating for reflection of parallel polarized light. The ECD grating used consists of a PZT ceramic with ten pairs of interdigital electrodes having 400 μm period on its surface. The characteristics of the grating and its application to an optical modulator are demonstrated experimentllly with a He−Ne 0.63 μm laser, obtaining a modulation of 60% with the applied peak voltage of 60 V at 24 kHz signal for the incident angle of 60°.     

Stimulated Raman adiabatic passage in fields with stochastic amplitudes

A theoretical analysis is presented of the effect of correlation between fluctuations of laser pulse amplitudes on population transfer between the states of a three-level atom coupled by the laser field. The carrier frequencies of the pulses are tuned to resonance with the transitions between the ground and excited states, |〈 and | 2〈, and the excited and metastable states, |2〈 and |3〈, in a lambda-type configuration. The laser pulses are timed so that population transfer between states |1〈 and | 3〈 is made possible by stimulated Raman adiabatic passage (STIRAP) in the absence of fluctuations. STIRAP does not occur when the laser fields are not correlated. When the fluctuations of one pulse amplitude duplicate those of the other, STIRAP can be observed for pulse amplitudes larger than those required in the absence of fluctuations.     

The opposite beams in He−Ne ring laser at 632.8 nm

Summary In the paper the resonant interaction of the opposite beams in a He−Ne ring laser at 632.8 nm is discussed on the basis of experimental results. These results show that the stable laser generation is attained when no simultaneous interaction of the opposite beams exists in the laser system. In the experiment, the mode-locking generation was obtained by applying a combining mirror, reflecting some part of the output beam into the laser cavity.

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Riassunto Nel lavoro si discute sulla base dei risultati sperimentali l’interazione risonante degli sciami opposti in un laser ad anello He−Ne a 632.8 nm. Questi risultati mostrano che la generazione laser stabile è raggiunta quando nessuna interazione simultanea di raggi opposti esiste nel sistema laser. Nell’esperimento, la generazione di modi vincolati in fase è stata ottenuta applicando uno specchio combinante, che riflette qualche parte del raggio di output nella cavità laser.

     

Optical phase conjugation and double-exposure phase-conjugate interferometry in dye-doped thin film using He–Ne laser

We have experimentally demonstrated optical phase conjugation and double-exposure phase-conjugate interferometry in a methyl green dye-doped gelatin film via degenerate four-wave mixing using a low-power He–Ne laser for the first time. The origin of phase conjugation associated with this dye-doped film is discussed. A phase-conjugate reflectivity of 0.13% is obtained with a He–Ne laser of total power 35 mW. PACS 42.65.Hw; 42.65.-k; 42.40.-i     

Acousto-optic Q-switched laser performances of Er^3＋：Yb^3＋：LuAl3（BO3）4 crystal at 1.5-1.6 μm

The cavity tuning characteristics of orthogonally polarized dual-frequency He-Ne laser at 1.15 μm are presented. Vectorial-extension model based on semi-classical laser theory reveals that cavity tuning characteristics are related to beat frequency, relative excitation, and type of Ne isotope. Distortions of cavity tuning curves become moderate with the increase of beat frequency because of the weakening of the crosssaturation effect. Distortions are enhanced with the increase of relative excitation because of the combined action of the self-saturation and cross-saturation effects. By adopting dual-isotope Ne instead of monoiso- toplic Ne, distortions are reduced because of the misalignment between peaks of the self-saturation and net gain coefficients. The theoretical calculations are in good agreement with the corresponding experimental results.     

High-frequency discharge stability of waveguide He-Ne lasers

The paper deals with the small-signal behavior and the stability of discharges in narrow capillaries. A theory is presented, which assumes that the time constants of the particle balance and the wall sheath extension determine the small signal behavior of a positive column. The column admittance is used to analyze the stability of an electric circuit typical for a He−Ne waveguide laser discharge. Numerical evaluation shows qualitative agreement of the experimental and the theoretical stability diagrams.     

Intracavity Raman laser generating a third stokes component at 1.5 μm

The lasing properties of an intracavity Nd:KGW Raman laser which converts the multimode radiation of an Nd:KGW laser operating on the ⁴ F _3/2–⁴ I _11/2 transition into the third Stokes component at a wavelength of 1.5 μm are studied. The energy in the third Stokes component is found to increase essentially linearly with the electrical energy delivered to the flashlamp. Lasing at the third Stokes component begins in the central portion of the Nd:KGW crystal and then propagates to its boundaries. Reducing the geometric aperture of the multimode pump beam in the Raman crystal lowers the divergence of the Stokes emission. For a source pump energy of 6 J, the intracavity Raman laser emits 14.7 mJ pulses of duration 3–4 nsec which are safe to the eyes. The divergence of the Raman laser beam at a level of 86% of the total energy is ≈ 9 mrad.     

Epitaxial growth of ferroelectric PLZT thin film and their optical properties

A series of experiments for growing epitaxial PLZT thin films has been made with rf sputtering. X-ray and electron diffraction analyses confirm that the fabricated films grow epitaxially on SrTiO₃ and MgO crystals. A good transparency in the region above 0.4 μm to infrared with good ferroelectric properties is obtained. Propagation loss of He−Ne laser light is less than 6 dB/cm, and the PLZT thin film is a promising candidate for the optical modulator and other functional elements for integrated optics.