Note: Demonstration of an external-cavity diode laser system immune to current and temperature fluctuations

We demonstrate an external-cavity laser system using an anti-reflection coated laser diode as gain medium with about 60?nm fluorescence spectrum, and a Rb Faraday anomalous dispersion optical filter (FADOF) as frequency-selecting element with a transmission bandwidth of 1.3?GHz. With 6.4% optical feedback, a single stable longitudinal mode is obtained with a linewidth of 69?kHz. The wavelength of this laser is operating within the center of the highest transmission peak of FADOF over a diode current range from 55?mA to 142?mA and a diode temperature range from 15?°C to 35?°C, thus it is immune to the fluctuations of current and temperature.     

Extended tuning of an injection-locked diode laser

We have investigated the application of an electronic feedback technique recently reported by Repasky et al. [Appl. Opt. 45, 9013 (2006)] to an injection-locked semiconductor diode laser. We find that without electronic feedback, the injection-locked slave laser will only follow the master for less than 1 GHz, but once the electronic feedback is applied, the slave laser is capable of following for more than 20 GHz, corresponding to the full scan range of the master laser.     

An oscillator circuit to produce a radio-frequency discharge and application to metastable helium saturated absorption spectroscopy

We present a rf gas discharge apparatus which provides an atomic frequency reference for laser manipulation of metastable helium. We discuss the biasing and operation of a Colpitts oscillator in which the discharge coil is part of the oscillator circuit. Radiofrequency radiation is reduced by placing the entire oscillator in a metal enclosure.     

Phase-shifting interferometer using a frequency-tunable diode laser calibrated by an optical frequency comb

We present a phase-shifting interferometer based on a frequency-tunable diode laser calibrated by an optical frequency comb and the Carre? algorithm. By use of the frequency control strategies of locking the diode laser to different comb modes and scanning the repetition rate, an arbitrary single optical frequency synthesizer is obtained. The relative laser frequency uncertainty is 5.7 × 10(-12) for 1 s averaging time with tracing to an Rb clock and accurate phase steps are achieved by optical frequency tuning. The surface topography of a standard sphere is measured by this phase-shifting interferometer based on a flat reference. The phase measurement repeatability is λ∕200. With this technique, phase measurement uncertainties from the laser frequency and phase steps are negligible.     

Creation of arbitrary spectra with an acousto-optic modulator and an injection-locked diode laser

We use a double-passed acousto-optic modulator (AOM), driven by an arbitrary waveform generator to produce multiple frequency components for a laser with arbitrary frequency spacings. A programmed sequence containing various sections of radio-frequency sinusoidal signal at different frequency is applied to drive the AOM. The diffracted light is used to injection-lock a diode laser. The combined techniques allow us to generate the multi-line spectra for the diode laser with arbitrary frequency spacings in the range of 100 MHz at a relatively high output power of 80 mW and a small power variation of 2%. Such a light source can be used in the application for laser cooling of molecules.     

Linewidth reduction of a distributed-feedback diode laser using an all-fiber interferometer with short path imbalance

The linewidth of a distributed-feedback (DFB) diode laser at 1156 nm, of which free-running linewidth was 3 MHz, was reduced to 15 kHz using an all-fiber interferometer with 5-m-long path imbalance. Optical power loss and bandwidth limitation were negligible with this short optical fiber patch cord. This result was achieved without acoustic and vibration isolations, and the frequency lock could be maintained over weeks. In addition to its simplicity, compactness, robustness, and cost-effectiveness, this technique can be applied at any wavelength owing to the availability of DFB diode lasers and fiber-optic components.     

Wave-number stability of a laser diode mounted in a closed cycle helium refrigerator

The wave-number stability of a laser diode mounted in a closed cycle helium refrigerator was examined using a CO(2) laser heterodyne spectrometer. The set current supplied by a commercial laser diode supply appeared stable enough over the time periods normally used. Temperature control was achieved through both passive and active loop control. A stage of open loop control of the cold tip allowed the closed loop control of diode heat sink to be operated at higher gains than conventionally used. Long-term stability of the center of the line shape function was better than 10 MHz per hour and the 1-min average was better than +/-5 MHz. Vibration of the diode mount determined the instrument line shape in spite of steps taken to eliminate the vibrations. The line shape had a half-width of 10 MHz with broad shoulders out to 50 MHz.     

Closed-loop wavelength stabilization of an optical parametric oscillator as a front end of a high-power iodine laser chain

We present a complex stabilization and control system for a commercially available optical parametric oscillator. The system is able to stabilize the oscillator's output wavelength at a narrow spectral line of atomic iodine with subpicometer precision, allowing utilization of this solid-state parametric oscillator as a front end of a high-power photodissociation laser chain formed by iodine gas amplifiers. In such setup, a precise wavelength matching between the front end and the amplifier chain is necessary due to extremely narrow spectral lines of the gaseous iodine (approximately 20 pm). The system is based on a personal computer, a heated iodine cell, and a few other low-cost components. It automatically identifies the proper peak within the iodine absorption spectrum, and then keeps the oscillator tuned to this peak with high precision and reliability. The use of the solid-state oscillator as the front end allows us to use the whole iodine laser system as a pump laser for the optical parametric chirped pulse amplification, as it enables precise time synchronization with a signal Ti:sapphire laser.     

Digital feedback stabilization of a single-axial-mode CO2 TEA laser

We have achieved long-term stability in producing high-power single-axial-mode CO2 laser pulses with a hybrid oscillator (TEA laser + low-pressure section) by using a novel digital feedback system that electronically adjusts cavity length.     

Low-cost method for stabilization of a CO2 laser for use in far infrared laser pumping

A simple and inexpensive technique for stabilization of a CO2 laser used to optically pump a far infrared waveguide laser is discussed. The technique uses the fact that the output power of the CO2 laser varies as the output frequency is swept through the Doppler profile of the emission line. Stabilization is obtained by adjusting the mirror separation and forcing the output power to remain constant at the level corresponding to the desired pump frequency.     

New approach to cathodoluminescence studies in application to InGaN/GaN laser diode degradation

Cathodoluminescence (CL) studies are widely applied in semi-conductor science and technology. However, for structures with a p-n junction the CL spatial distribution can be strongly affected by internal current flows of the electron beam induced current generated within the structure. This influence is the investigated in application to CL studies of degradation in aged laser diodes with InGaN multiquantum wells.     

The installation to study the prebreakdown stage of a gas discharge by laser probing

An installation to study a pulsed gas discharge in a diode with a single metal tip by laser probing has been devised. The installation represents a generator comprised of cable sections connected to a five-channel laser-triggered switch. The synchronization of the probing laser beam with the voltage pulse is not worse than ~1 ns. The moment of probing is determined by the optical delay and can be varied independently within the range of 10–20 ns by changing the charging voltage of the cables. The pressure in the discharge chamber can be varied from 10^–5 Torr to atmospheric pressure. Copper or molybdenum wires with a diameter of 10 μm or greater were used as cathode pins. Three independent optical record channels with time delays of 2 and 13 ns relative to the first channel allow one to simultaneously obtain interferograms and shadow and schlieren images of the discharge gap with spatial and time resolutions of 20 μm and 70 ps, respectively, with the exposure time of each frame being equal to a laser pulse duration of 70 ps. Using the devised installation, qualitative and quantitative data on the prebreakdown processes that occur in a tip-type diode have been obtained within a wide range of pressures.     

Measurement of temperature of laser cooled atoms by one-dimensional expansion in a magneto-optical trap

We discuss a simple time of flight technique for measurement of temperature of a cold cloud in a magneto-optical trap (MOT). The technique is based on spatiotemporal fluorescence imaging of the cloud that is allowed to undergo one-dimensional expansion in the presence of the orthogonal two-dimensional configuration of laser beams by temporal modulation of a pair of counterpropagating trapping beams in the MOT. We show that, in the time scale 0< or =t<5 ms, the expansion of the cloud is ballistic and the temperature can be extracted from the time variation of the rms size of the cloud in the expansion direction. The reliability of the technique has been established by comparing the results with release and recapture method, and also by fitting them to the known temperature scaling law.     

Synchronization of a millimeter-band oscillator on an avalanche-transit diode

Experimental results from investigations of the synchronization band of an 8-mm-band oscillator on an avalanche-transit diode are given. The dependencies of the synchronization band on the parameters of the generators oscillating system and the supply current of the avalanche-transit diode are presented.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 101–102.Original Russian Text Copyright © 2005 by Alekseev, Maliev, Nashchanskii.     

Influence of high-power diode laser heat treatment on wear resistance of a mold steel

The effect of hardness on wear loss and wear behavior during fretting was studied. A high-power diode laser was used to achieve the surface hardening of a mold steel (AISI P20-improved) at temperatures of 1000 and 1200 °C. A hardness increment was detected in laser heat-treated specimens, which may be attributed to phase transformation from ferrite to martensite, influencing wear loss and fretting wear behavior. In the fretting test results, smaller wear scars and less wear loss were observed for laser heat-treated specimens in comparison to those of base metal. Moreover, relatively more stable friction coefficient profiles were obtained for the laser heat-treated specimens due to uniform contact characteristics at two contacting surfaces. The effectiveness of the proposed technique was verified by the morphology of the wear scars of the treated specimens, which had a smooth appearance and minor abrasion grooves.

     

Design of a compact cw chemical HF/DF laser using a microwave discharge

A compact cw chemical HF/DF laser is described. The laser system consists of a microwave discharge using a surfatron to dissociate SF6 molecules mixed with He, a reaction chamber engineered to provide a fast mixing of reacting atoms and molecules, and an optical resonator which includes a concave mirror and a blazed grating for line selection, both mounted on a rigid Invar frame. The laser oscillates on a single line single TEM00 mode over many P transitions of HF and DF with a typical intensity fluctuation of 5% and a frequency jitter of about 30 MHz.     

Development of a wavelength-stabilized distributed bragg reflector laser diode to the Cs-D2 line for field use in accurate geophysical measurements

We have developed a wavelength-stabilized laser diode (LD) for geophysical measurement devices, which benefit from the uniformity of laser light. Regarding this purpose, a system that has such characteristics as low power consumption, sturdiness against mechanical disturbances, and a long life with long-term frequency stability is especially required. Therefore, we adopt as the light source a distributed Bragg reflector (DBR) LD because it has various advantages concerning such properties. This paper describes the durable and compact wavelength-stabilized laser system. Since our DBR-LD oscillates at 852 nm, we selected the Cs-D2 line (6 2S1/2-6 2P3/2 transition) as a frequency reference to obtain a long-term stability in wavelength. Stabilization is performed by a feedback system using a modulation transfer (MT) method, which is a kind of Doppler-free saturated absorption spectroscopy, to acquire a saturated absorption signal with a high signal-to-noise ratio. Using this system, we could continuously lock the laser frequency to the hyperfine component of the Cs-D2 line for more than one week. By an Allan standard deviation measurement, the uncertainty of the stabilized laser frequency was found to be better than 1 x 10(-10) (<40 kHz) in a Gatetime region longer than 100 s.     

Frequency selection of the radiation of a fiber laser with a reflection interferometer

This paper considers the results of using a two-mirror multiple-beam reflection interferometer (RI) which has a response function in reflection similar to the response function of a Fabry-Perot interferometer in transmission. The two-mirror cavity of the RI included two flat mirrors, one of which was highly reflective, and the other had an asymmetric coefficient of reflection from different sides. The light reflected from the RI was brought to an optical fiber through a collimator lens. The optical fiber, collimator, and RI constituted an integrated fiber RI, which was first used for continuous tuning of the wavelength of an erbium ring fiber laser with a continuous generation in the spectral range 1520–1566 nm.     

可调谐激光器激光波长宽范围自动偏频锁定

针对激光多波长干涉绝对测距中构建多级合成波长的需求,提出了一种锁至飞秒光频梳的可调谐激光器(External Cavity Diode Laser,ECDL)输出激光波长的宽范围自动偏频锁定方法.首先,设计了光栅+双凸透镜梳齿滤波的拍频信号探测单元,实现了宽范围ECDL激光波长与目标梳齿的拍频探测.接着,采用锁相放大原...     

Analysis and design of coaxial nozzle with rectangular outlet for high power diode laser in laser metal deposition

High power diode laser (HPDL) characterized by a wider rectangle beam spot (RBS) with top-hat intensity distribution is particularly applied in laser metal