用于氢原子1S-2S光谱研究的超窄线宽243nm半导体激光

近年来,随着激光稳频技术的发展,人们可以把972nm的外腔半导体激光器产生的激光进行放大和四倍频,并将它锁定到超稳定的光学法布里-珀罗腔上,从而可以获得Hz量级超窄线宽的243nm激光,使其成为研究氢原子1S-2S双光子跃迁的有力工具.文章主要介绍了超稳腔、四倍频243nm半导体激光器的研究进展及在氢原子1S-2S双光子跃迁精密光谱研究中的应用.     

用于氢原子1S-2S光谱研究的超窄线宽243nm半导体激光

近年来,随着激光稳频技术的发展,人们可以把972nm的外腔半导体激光器产生的激光进行放大和四倍频,并将它锁定到超稳定的光学法布里-珀罗腔上,从而可以获得Hz量级超窄线宽的243nm激光,使其成为研究氢原子1S-2S双光子跃迁的有力工具.文章主要介绍了超稳腔、四倍频243nm半导体激光器的研究进展及在氢原子1S-2S双光子跃迁精密光谱研究中的应用.     

Intra-cavity spectroscopy with diode lasers

A multi-mode diode laser with an external cavity is studied experimentally and theoretically for its application to intra-cavity spectroscopy. One facet of a typical Ga_0.89Al_0.11As laser diode was antireflection-coated by deposition of HfO₂ such that 10^–3 residual reflectivity was left over. This diode was placed in an external optical cavity. The emission spectrum of this diode laser is highly sensitive to any frequency-dependent loss in the cavity, and the detectivity of such a loss grows with the pump rate. Even close to threshold, the absorption at 780 nm of Rb atoms with a density of 5×10¹⁰ cm^–3 has been detected. An adequate model for diode lasers based on rate equations and including frequency-dependent gain saturation is developed and applied to the calculations of output spectra. The sensitivity of these spectra to intra-cavity absorption is determined by the overall cavity loss — which is rather high — and the fraction of spontaneous emission in the total emission, in contrast with dye lasers where it is limited by nonlinear mode coupling. Various criteria for the sensitivity are suggested. The smallest detectable absorption with a perfectly antireflection-coated laser is 10^–6 cm^–1. Improvement of the characteristics of the laser diode would increase the sensitivity.     

High-sensitivity transient spectroscopy using tunable diode lasers

Experimental techniques have been developed to monitor transient infrared absorptions using lead-salt tunable diode lasers. The techniques are easily implemented, yield sensitivities which are limited by detector noise at 10^–5 level of absorbance, and have a response time on the order of one microsecond. The transient absorption detection techniques are high frequency versions of the sweep integration technique pioneered by Jennings [Appl. Opt.19, 2695 (1980)]. TDL modulation rates of 100 kHz and 500 kHz allow for absorption sampling rates of 200 kHz and 1 MHz, respectively. In order to reproducibly achieve near-detector-noise-limited sensitivities for 100 kHz TDL modulation rates, an automated analog subtraction circuit has been developed which removes the effects of minor TDL power variations. At the 500 kHz modulation rate, digital filtering techniques are used to remove the effects of this power variation.     

Compact, filtered diode laser system for precision spectroscopy

Stable, narrow-linewidth optical sources are necessary in modern atomic physics. An appealing approach to achieving approximately 10 kHz frequency stability is optical feedback. We have designed a compact external cavity diode laser with optical feedback to a filter cavity mounted on a single baseplate and enclosed inside a vacuum sealed box. The design was implemented for three wavelengths addressing the 422 nm cooling, 1091 nm repumping, and 674 nm clock transition lines of Sr(+). We are able to cool a single, trapped strontium ion to approximately 2 mK and observe motional sidebands of the 5S(1/2) <--> 4D(5/2) transition.     

Application of pressure-tuned diode lasers to high-resolution spectroscopy

The application of the high-pressure chamber with a pressure transmitting medium (liquid at room temperature) to diode-laser tuning was found to be a useful method for high-resolution spectroscopy. Ammonia absorbtion spectra in the 10 μm region were recorded with a resolution approaching the Doppler limit.     

High frequency wavelength modulation spectroscopy with diode lasers

High frequency wavelength modulation spectroscopy with diode lasers is accomplished by dithering the drive current at RF frequencies as high as 250 MHz. This technique is useful for fast and sensitive detection of absorption lines in the near-and mid-infrared spectral regions. Detection of 300 MHz wide spectral features corresponding to 1% changes in transmission is accomplished in time intervals as short as 500 ns. A potential application is for fast reading of information contained in frequency domain optical memories based upon photochemical hole burning.     

Wavelength modulation spectroscopy based on quasi-continuous-wave diode lasers

A modified wavelength modulation spectroscopy（WMS）based on the self-heating effect of the tunable diode laser when driven in quasi-continuous-wave（QCW）mode is investigated.A near-infrared distributed feedback（DFB）diode laser working at the QCW mode is employed as the QCW light source,and CO2 is selected as the target gas.The characteristic of the QCW second harmonic（2f）line profile is analyzed through a comparison with that of the traditional CW WMS with the same system.A noise-equivalent absorbance of 3.2×10-5 Hz-1/2 for CO2 at 1.58μm is obtained with 18-m optical path.The QCW WMS lowers the dependence on lasers and expands selectivity,thus verifying the feasibility of the method.     

Atomic gallium laser spectroscopy with violet/blue diode lasers

We describe the operation of two GaN-based diode lasers for the laser spectroscopy of gallium at 403 nm and 417 nm. Their use in an external cavity configuration has enabled us to investigate of absorption spectroscopy in a gallium hollow cathode. We have analyzed the Doppler-broadened profiles, accounting for hyperfine and isotope structure and extracting both the temperature and density of the neutral atomic sample produced in the glow discharge. We have also built a setup to produce a thermal atomic beam of gallium. By using the GaN-based diode lasers, we have studied the laser-induced fluorescence and hyperfine-resolved spectra of gallium. PACS 42.55.Px; 42.60.-v; 32.30.-r; 03.75.Be     

Polarization spectroscopy of atomic oxygen by dye and semiconductor diode lasers

Summary We used polarization spectroscopy to perform a high-resolution investigation of atomic oxygen in the visible and near-infrared spectral region by means of dye and semiconductor diode lasers. We measured the fine structure of the highly excited 4d ⁵ D level and resolved the hyperfine structure of the metastable 3s ⁵ S ₂ level of¹⁷O. Isotope shift values are also reported for several transitions of the three stable oxygen isotopes (¹⁶O,¹⁷O,¹⁸O). Polarization lineshapes are discussed and compared with those obtained in saturation techniques.     

High-brightness diode lasers

The basic concepts and some modelling aspects of high-brightness semiconductor lasers are reviewed. The technology of lasers with a tapered gain-region is described. They provide the highest brightness of a semiconductor source with continuous wave emission in the visible and near infrared spectral range. Experimental results are presented for tapered lasers emitting at 735 nm and 808 nm. Output powers of 3 W were achieved in nearly diffraction limited beams. To cite this article: H. Wenzel et al., C. R. Physique 4 (2003).     

Differential Helmholtz resonant photoacoustic cell for spectroscopy and gas analysis with room-temperature diode lasers

The results of theoretical and experimental studies and the design of a multi-purpose differential Helmholtz resonant photoacoustic detector (DHRD) and its applications to high-resolution spectroscopy of molecular gases and gas analysis with a room-temperature diode laser in the near-IR region are summarized. The series of experiments and numerical analysis of the DHRD sensitivity were performed for both types (single-pass and multi-pass) of DHRDs within a wide pressure range 0.1–101 kPa, including the regime of a gas flowing through a DHRD cell. The hardware and electronic arrangement of DHRDs for diode laser spectrometers and gas analyzers providing a limiting absorption sensitivity better than 10^-7 Wm^-1 are described. The results of measurements of spectral line parameters of H₂O near 800 and 1390 nm and CH₄ near 1650 nm (intensities, line broadening and shifting by atomic and molecular gases) are presented and discussed. The problems and the ways of perfection of the methodology and accuracy of DHRD techniques with tunable diode lasers of near-IR and visible spectral ranges are discussed. Received: 1 April 2002 / Revised version: 20 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +7/382-225-8026, E-mail: kvan@asd.iao.ru     

Rate equation approach for diode lasers

The light output and the electron density within the active layer of a semiconductor laser have been calculated from the steady state solution of a rate equation approach. The assumed rate equation model takes into account the spontaneous emission into the lasing modes. Simple analytical approximation formulae have been found under the assumption of a power-law dependence between optical gaing and electron densityn (g ∞n′). The approximations are compared with numerical results from the rate equations. With the exception of a small region near the lasing threshold good agreement has been found. The theoretical results are compared with experimentally measured light outputs from single and double heterostructure lasers. From the comparison below threshold the power law exponent/may be evaluated. The comparison at threshold suggests that the spontaneous emission term decreases at threshold. This decrease is in agreement with experimentally measured changes of the emission bandwidth at threshold.     

Electroreflectance vibrational spectroscopy: A new surface analysis technique using diode lasers

A new infrared technique to measure the vibrational spectra of adsorbed molecules is introduced. An Infrared active mode of an oriented molecule has a first order Stark effect. Therefore, infrared absorption by oriented adsorbed molecules is modulated by an alternating electric field. The spectra is obtained by measuring this using a diode laser. The advantages and limitations of Electroreflectance Vibrational Spectroscopy (EVS) are discussed. We calculate the Stark tuning rate and consequent signal amplitude for a number of diatomic molecules. Measurements of diode laser Intensity noise are used to estimate the signal to noise ratio for comparison with other techniques.     

Interference-filter-stabilized external-cavity diode lasers

We have developed external cavity diode lasers, where the wavelength selection is assured by a low loss interference filter instead of the common diffraction grating. The filter allows a linear cavity design reducing the sensitivity of the wavelength and the external cavity feedback against misalignment. By separating the feedback and wavelength selection functions, both can be optimized independently leading to an increased tunability of the laser. The design is employed for the generation of laser light at 698, 780 and 852 nm. Its characteristics make it a well suited candidate for space-born lasers.     

Finite-element thermal model for buried-heterostructure diode lasers

First results of our new finite-element modelling of thermal properties of GaAs/(AlGa)As buried-heterostructure (BH) lasers are reported. The calculus procedure is very efficient, so we have used a standard IBM PC/XT microcomputer. For the stripe active-region width of 1 m, the thermal resistance of the laser was determined to be about 70 KW^-1, whereas its electrical resistance was about 6 ohms. To the best of our knowledge, isothermal lines within BH lasers have been obtained for the first time. The isothermal configuration enables us to analyse heat-spreading phenomena in BH lasers, which makes possible thermal optimization of the laser construction.As the first application of the model, the relative influence of the oxide layer thickness on the laser thermal resistance was examined. Because of relatively large lateral dimensions of the laser crystal as compared to the active region, this influence is often neglected, whereas our detailed calculations reveal its importance. An increase in this thickness from 0.1 m to 0.5 m is followed by over 15% increase in the laser thermal resistance.     

Tunable diode lasers and two-tone frequency modulation spectroscopy applied to atmospheric gas analysis

In this paper, we discuss the main features of a class of gas analyzers based on spectroscopic techniques with the aim of realizing fully automated systems which can be used for practical purposes. The technique we deal with is based on semiconductor diode laser as sources, emitting in the near infrared region of the electromagnetic spectrum, and the two-tone frequency modulation spectroscopy as the detection technique. We will describe the main features of a typical device and two particular apparata for industrial and biological applications.     

High-power broad-area diode lasers for laser cooling

Received: 1 April 1996/Revised version: 24 September 1996