Semiconductor lasers with weak optical injection: a laser as a low-signal detector
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Summary form only given. The main idea of optical injection is to give a reference to the injected laser from another laser. The injected laser can become slaved onto the master and frequency-locking occurs following the injected intensity and the frequency difference between both lasers. Phase locking is a different phenomenon which manifests itself in the locking of the linewidth of the slaved laser onto that of the master. The topics of this communication is to describe the power spectral density of the injected laser when the injected power is decreased to very low level (/spl sim/picowatt) with a central frequency identical for both lasers but each of them having very different linewidths. The study follows from an interpretation of the laser as a filter and amplifier as recently given.Keywords:
Laser linewidth
Injection locking
SIGNAL (programming language)
We present an external cavity diode laser which is frequency coupled to a stabilized He-Ne Laser with optical phase locked loop technology. For long term frequency stability the diode laser is locked with a fixed frequency offset to a stabilized He-Ne Laser at 633nm. A commercial PLL chip and the piezo-drive of the diode laser are used for precise frequency control. With this simple technique we develop a diode laser source which reach the frequency stability of a stabilized He-Ne Laser and still provide an optical output power of 5 mW or more. This high optical output power enables applications like multi axis homodyne interferometry with just one laser source.
Vertical-cavity surface-emitting laser
Laser diode
Laser linewidth
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In this paper we investigate experimentally the dynamical response of a class B microchip laser submitted to optical feedback. Based on the theoretical model for a laser with optical feedback, we demonstrate how the effects of the optical reinjection of the laser beam reflected by an object situated in front on the laser can be used in determining the characteristics of the object (reflectivity and distance to the laser). In this purpose we have constructed a laser system, which we further use in an optical feedback experimental setup. The laser we use in our experiment is a class B Nd:YAG microchip laser, which has a damping rate of the laser cavity γc much higer than the damping rate of the population inversion γ1. The laser has a cavity lenght L=0.8mm, operating at λ=1,064&mgr;m. In order to obtain the laser emission, the active medium is pumped by a system of laser diodes emitting at 810nm. This type of laser has the relaxation oscillations at a characteristic frequency, named relaxation frequency. For the maximum pump parameter η≈6 the maximum output power of the laser is Pout≈130mW and the relaxation frequency fr≈1MHz. The value obtained for γc/γ1≈1,7X106>>1 proves that our laser is a class B laser and also that it can be successfully utilized for optical reinjection. Based on this laser system, we develop a method for exploiting the sensivity of the Nd:YAG laser to the optical reinjection. We demonstrate that the optical feedback modifies the steady state of the laser and changes the laser characteristics. This method is based on the high sensitivity of this type of laser to the optical reinjection. In order to analyse the effects of the optical feedback on the laser behaviour, we placed an object at the distance d in front of the laser and the retro reflected beam was reinjected into the laser cavity. We use a beam splitter to send a small fraction of the laser beam to a photodiode. The signal provided by this photodetector is sent to an oscilloscope, where we observe the signal and the power spectrum of the laser. Our experimental results show that the optical feedback modifies the laser characteristics. We observe that the optical feedback induces a significant amplification of the laser signal and also a deplacement of the relaxation frequency to smaller values. Our experimental results are in good agreement with the mathematical model. By introducing the reinjected electric field into the equations for the dynamical behavior of a class B laser, it can be shown that the reinjection of a wave with the same pulsation as the laser beam determines a changement of the steady state values for the population inversion, for the electric field and also for the optical frequency of the laser. Based on the the equations for laser intensity and for the relaxation pulsation in the presence of the optical feedback, we determine experimentally the reflectivity of the object and the distance between laser and object. We conclude that the class B lasers present a high sensitivity to the optical feedback, which induces the change of the steady state of the laser. This modifications can be succesfully used for determining the characteristics of differents objects submitted to laser irradiation.
Population inversion
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High-brightness, high-power diode laser arrays are expanding their role in pumping multilevel solid-state laser systems. Various advanced solid-state laser systems take advantage of strong but narrow absorption lines and thus, demand a very small linewidth of the pump source. Conventional diode laser bars cover only the lower part of required brightness range and have typically a broad emission spectrum. In this work, we describe a laser diode array source consisting of broad area laser diodes utilizing an angled-grating distributed feedback (/spl alpha/-DFB) structure operating at a wavelength of 960.5 nm, which is an absorption line for Er:YAG solid-state material lasing near 3 /spl mu/m. Because the gain for this laser transition is quite low, the performance is strongly dependent upon the spectral and spatial quality of the pump beam. In order to obtain adequate power from the laser, a pump source is required which could deliver several watts of power into a 50 /spl mu/m spot within less than 0.3 NA with a spectral bandwidth of <1 nm at precisely 960.5 nm.
Laser linewidth
Gain-switching
Laser diode
Optical Pumping
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The authors report the performance of a laser-diode-pumped Nd:glass laser. Using the AM active mode-locking technique, pulses as short as 9 ps were obtained. The development of a high-power (415 mW), high-optical-slope-efficiency (32.4%) laser-diode-pumped Nd:glass laser using high-power, broad stripe laser diodes as the pump source is described. Single-frequency operation of the Nd:glass laser using an acoustooptic modulator to ensure unidirectional operation in a ring laser configuration was investigated. An instantaneous linewidth of less than 300 Hz was observed.< >
Laser linewidth
Optical Pumping
Laser diode
Neodymium
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In development of a known method of an regenerative amplification of low-power picosecond pulses (the injection seeding method) its modification: the method of injection locking of master laser with the amplifying laser (laser with short-term resonance modulation of losses--STRML-laser) is offered. The use of the STRML-laser as the regenerative amplifier allows to lower a level of the laser-injector power on two-four order. For the neodymium laser with an output pulse energy 1 - 2 J this power can be lowered up to 1 W, and the reliable capture can be carried out with 5 W. It enables to realize the circuit of self-injection in the STRML-laser by adding a nonlinear passive modulator in a cavity. Thus at a beginning of linear stage it is possible to `sow' pulses resulting in generation of much more short on a comparison with realized in a STRML-regime with preservation of remaining positive qualities of this laser.
Neodymium
Self-pulsation
Picosecond
Modulation (music)
Q-switching
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We demonstrated a efficient 532-nm microchip laser with a conventional schematic pumped by a single-mode laser diode through a ball lens. An output power as high as 18.7 mW has been achieved for a 121-mW pumping power of the laser diode. We also investigated the temporal dynamic characteristic of the laser by numerically solving a set of rate equations.
Schematic
Laser diode
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A powerful single-mode distributed bragg reflector tapered diode laser with a low-noise automatic power supply has been developed. The output characteristics of the tapered diode laser are investigated. Using such laser as a pumping source, the free running mode of a Yb:KYW laser is obtained and investigated. It is shown that a compact precision femtosecond frequency synthesizer based on a Yb:KYW laser pumped by a diode laser of the similar type can be created.
Ytterbium
Vertical-cavity surface-emitting laser
Relative intensity noise
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A noninvasive technique was developed to measure the temperature distribution in laser gain medium. Both axial and radial temperature distributions of a diode-laser-pumped and intracavity frequency-doubled high-power Nd:YVO4/KTP laser were characterized using a high dynamic range, low-coherence reflectometer. This measurement is important to the design of high-power solid-state lasers both in terms of mode matching and laser-rod doping selection.
Reflectometry
Solid-state laser
Optical Pumping
Laser diode
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This paper reports what we believe to be the first finding that, in laser diode- pumped solid-state lasers, the mode hopping of the pumping laser causes the noise in the solid-state laser. The mode hopping results from the optical feedback into the pumping laser diode, which is reflected from the solid-state laser material facet in excess of a certain amount.
Vertical-cavity surface-emitting laser
Solid-state laser
Optical Pumping
Laser diode
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