This novel approach employs a closedloop control based on polarization spectroscopy. As noted above, the split cavity laser is relatively susceptible to external vibration. Design and development of an external cavity diode laser for. Externalcavity diode lasers ecdl have widespread applications in optical and. Aug 09, 2010 diodenlaser 405nm, sfaw210 mit externem resonator mit littrowaufbau. The external cavity diode laser is optimised and characterised near 780 nm. Diode lasers unlike leds will not operate below a threshold current. We have seen in a previous article that external cavity diode lasers ecdl have a narrowlinewidth laser spectrum. An external cavity laser, or ecl, is a laser with a reflector that creates the cavity outside of the gain chip and allows the cavity to be longer than if it was confined to the gain chip.
Results obtained in this study indicate that the external cavity diode laser is suitable for future applications in spectroscopy and laser cooling of neutral rubidium atoms. An external cavity must be used to improve the diode laser performance, usually at the cost of a significant increase in the device dimensions. The usual open cavity diodelaser oscillators require the use of optical isolators to protect the cavity from unwanted optical coupling. External cavity diode lasers are tunable lasers which use mainly double heterostructures diodes of the al x ga 1x as type. Peter beyersdorf department of physics and astronomy dr. In addition, a laser diode contains an optical cavity where stimulated emission takes place. Characterization and development of an extended cavity tunable laser diode by fnu traptilisa approved for the department of physics and astronomy san jose state university may 2014 dr. The purpose of this laser diode tutorial is to provide the information necessary to create a long lifetime, stable laser diode system. While collimating the output of a diode laser is a relatively simple problem to solve with lenses, narrowing the bandwidth of the output requires construction of an external cavity. Apr 06, 2018 an external cavity laser, or ecl, is a laser with a reflector that creates the cavity outside of the gain chip and allows the cavity to be longer than if it was confined to the gain chip. Slope efficiency of integrated external cavity hybrid lasers.
In addition, the wavelength shift with temperature of 0. Traditional narrow linewidth, tunable diode laser sources are based on the external cavity diode laser ecdl, where an external diffraction grating is used to select the single longitudinal mode and realize the wavelength tuning. Diode laser chip modes this graph shows the chip modes for a typical sharp lto24 780nm laser diode. In this paper, we derive a model capable of describing multicavity laser systems with polarizationdependent elements. External cavity laser diodes fibercoupled laser diodes. An externalcavity diode laser is a diode laser based on a laser diode chip which typically has one end antireflection coated, and the laser resonator is completed with, e. Kockar, examination of feasibility of using breath ammonia analysis based on offaxis cavityenhanced absorption spectroscopy with external cavity diode laser for noninvasive realtime diagnosis of helicobacter pylori, appl. They are used in optical communication and fibre sensor technology. The first externalcavity diode lasers used intracavity etalons and simple tuning littrow gratings.
In this project we have created an external cavity diode laser ecdl, which selects a single wavelength from the entire output spectrum of the diode laser and drives the laser at this wavelength. Recently, we have demonstrated large modehop free tuning of an external cavity diode laser with an offtheshelf laser diode. The first external cavity diode lasers used intracavity etalons and simple tuning littrow gratings. Changing the external cavity length l e by varying v pzt, while holding the injection current fixed, tunes the.
Expanding 1 and using fourier components leads to e e0. A semiconductor can be doped so that it has either an excess of electrons pdoped or holes lack of electrons, ndoped. External cavity diode lasers tuned with silicon mems. External cavity laser diodes with frequencyshifted feedback. Demonstrates how selective feedback creates an extremely stable laser source. Stabilizing diode lasers to h ighfi n esse cavltl es fox. This requires the preselection of a diode for the targeted wavelength.
Second generation external cavity diode lasers for liyb. All wavelengths that fit in the chip by an integral number of halfwavelengths gain intensity. External cavity diode lasers show great promise for use in differnt applications, from high resolution spectroscopy, wide bandwidth comunication network systems to vaporrate monitoring systems. An external cavity diode laser using a volume holographic. External cavity diode laser setup with two interference filters. Modehopfree tuning over 5 ghz of external cavity diode. The latter is also expected from a laser diode in an external cavity where the laser light is seeded by spontaneous emission. Interference lter stabilized external cavity diode laser. External cavity diode lasers are common tools in undergraduate and graduate laboratories. Modulation enhancement of a laser diode in an external cavity 303 modulating the current injected into the diode with a sine wave will induce a phase in the electric. Much of what will be discussed will be in general terms of laser diode performance, warnings, and tips. Modulation enhancement of a laser diode in an external cavity. Frequency locking of an external cavity diode laser.
Diodenlaser 405nm, sfaw210 mit externem resonator mit littrowaufbau. Thus, by using optical feedback from a diffraction grating, we are able to narrow the total bandwith. The lens is chosen to compensate for abberations arising from the diodes packaging window. Bright tunable external cavity diode laser using a micromachined silicon flexure and a volume holographic reflection grating for applications in atomic optics, journal of micronanolithography, mems, and moems 72, 021010 1 april 2008. Painter california institute of technology abstract anenhancedtunablelittrowcon. Osa externalcavity diode laser using a grazingincidence. Richter and hansch 4 report a continuous line broadening up to 5 ghz using an 850 nm infrared laser diode of 30 mhz free running bandwidth in such an external cavity. Breath analysis using external cavity diode lasers.
Tunable external cavity diode laser using a micromachined. Construction and characterization of external cavity diode. Fang abstract in this report, a model of external cavity semiconductor laser is built, and then based on this model a program is coded for simulating the thermally induced wavelength shift and mode hopping. Highlights we present an external cavity diode laser ecdl system. The laser will oscillate at a wavelength resonant with the external laser cavity between the diode rear facet and the grating. Hochiao chuang, ricardo jimenezmartinez, simon braun, dana z. We successfully apply it to explain the peculiar form of our. This configuration allows a gaalas diode laser to be tuned conveniently anywhere in a range greater than 20 nm.
Compact tuneable external cavity diode laser ecdl with diffraction limited 500 mw, and their application in bec and crds sandra stry, richard knispel, lars hildebrandt and joachim sacher sacher lasertechnikgroup, hannah arendt str. The second approach is external cavity feedback technique used to improve the spectral quality of the highpower gan diode lasers and make the lasers tunable, 14. Due to the extreme sensitivity of laser frequency to cavity length 25mhznm for a 780nm diode, the grating mount, which is typically adjustable to allow for laser alignmentandtuning,shouldberigid. Interference filter stabilized external cavity diode laser toronto. Pdf mode stability of external cavity diode lasers. The purpose of this research project is to implement and test an electronic control system for an external cavity diode laser. A gratingtunable externalcavity laser based on a semiconductor laser diode a thesis for the degree of master of science presented to dublin city university by brian kevin hurley b. This spectum was obtained with no external cavity and the laser running at a current just below threshold. Apr 01, 2008 hochiao chuang, ricardo jimenezmartinez, simon braun, dana z. A semiconductor diode laser having a modified littrow external resonator is described. But it is interesting to look at the characteristic curve to. This document may contain or reference information and products protected by. Nov 23, 2015 we have seen in a previous article that external cavity diode lasers ecdl have a narrowlinewidth laser spectrum. They are used in optical communication and fiber sensor technology.
Laser structure and principle of operation laser diodes consist of a n diode with an active region where electrons and holes recombine p resulting in light emission. An additional output coupling mirror in a vshape configuration of the resonator makes the system more efficient and convenient to operate. The light emitted from the diode dl is collimated by an objective lens lc with short focal length 3 to 4. The laser system is based on a highpower gan diode laser in a littrow external cavity.
Osa model for tuning an externalcavity diode laser by. Design and development of an external cavity diode laser for laser. External cavity diode lasers offer more stable output frequency and narrow spectral. Narrow linewidth tunable external cavity diode laser using. A typical 850 nm laser diode with a length of around 300 m and a group index around 4 will have a longitudinal mode spacing of 0. Changing the external cavity length l e by varying v pzt, while holding the injection current fixed, tunes the external cavity mode frequency across the peak of the. Ramendra bahuguna department of physics and astronomy dr. Externalcavity diode lasers are nonmonolithic diode lasers where the laser cavity resonator is completed with external optical elements. Narrowbanded ecl lasers are characterized by a very small line width, low noise, and very good wavelength stability. We achieved this by using a short external cavity and by simultaneously tuning the. Pdf external cavity diode laser with kilohertz linewidth. The laser cavity consists of a waveguide terminated on each end by a mirror. Jul 17, 2007 demonstrates how selective feedback creates an extremely stable laser source. U100p2k mount to provide for manual translation of the grating and mirror.
Changing the length or refractive index of the cavity, for example by heating or cooling the laser diode, will shift the whole comb of modes and. Characterization and development of an extended cavity tunable. External cavity diode laser spectrum in modehopfree range. Modehopfree tuning over 140 ghz of external cavity diode.
Externalcavity diode lasers are tunable lasers which use mainly double heterostructures diodes of the al x ga 1x as type. Compact tuneable external cavity diode laser ecdl with. Stabilizing diode lasers to h ighfi n esse cavltl es. Both a holographic diffraction grating and a ruled diffraction grating are used as feedback elements in the. If brought together, thus creating a pn junction, a region. Ultralow noise miniature external cavity semiconductor laser.
The diode cavity is called the intrinsic or internal cavity. External cavity diode laser setup with two interference filters 1 3 page 3 of 6 298 width of typical infrared diodes. At the end a step by step instructions manual for building one of these ecdls is given. We report a homebuilt external cavity diode laser ecdl, using a diode whose front facet is not antireflection ar coated, that has a modehopfree mhf tuning range greater than 140 ghz. Characterization and development of an extended cavity. This is an instructional paper to guide the construction and diagnostics of external cavity diode lasers ecdls, including component selection and optical alignment, as well as the basics of frequency reference spectroscopy and laser linewidth measurements for applications in the field of atomic physics. A diode laser is simply a light emitting diode led with a feedback cavity. Developing an electronically controlled external cavity diode laser. It uses a diffraction grating at grazing incidence for wavelength selection and output coupling. The laser system is based on a highpower gan diode laser in a littrow externalcavity. External cavity laser diodes ecls are lasers with a very small line width, very good wavelength stability, and very low noise. The basic idea is to use an extended cavity diode laser with the 1st order diffraction. Sc school of physical sciences dublin city university research supervisor.
Tuning this cavity length across a wavelength allows the laser to be tuned across a free spectral range c2 l around the grating gain peak where c, is the speed of light and l, is the cavity length, typically 1. External cavity diode lasers yield stable output frequency and narrow spectral bandwidth by exploiting the sensitivity of diode lasers to external optical feedback. An external cavity diode laser is a diode laser based on a laser diode chip which typically has one end antireflection coated, and the laser resonator is completed with, e. The usual open cavity diode laser oscillators require the use of optical isolators to protect the cavity from unwanted optical coupling. One can tune and stabilize inexpensive laser diodes as will be done here to be used in contexts such as high precision optical metrology and spectroscopy experiments. Due to the arcoating on the laser diode, there is just a weak resonator in the bare laser diode. Consequently, only when the threshold current is reached will the diode commence lasing.
Design and characterization of a littrow configuration external. Pdf singlefrequency external cavity green diode laser. The external cavity length and the diode mode have been chosen so that the overall gain peak occurs at. Light emitted by a diode laser is not monodirectional and typically has a large bandwidth.
Also, the linewidth is reduced by a factor of more than from 40 mhz to less than 10 khz. We achieved this by using a short external cavity and by simultaneously tuning the internal and external modes of the laser. A laser cavity built in this manner is often called an ecdl, extendedcavity diode laser, or externalcavity diode laser. External cavity diode laser with kilohertz linewidth by a monolithic folded fabryperot cavity optical feedback. Design of external cavity semiconductor lasers to suppress wavelength shift and mode hopping l. Recently, we have demonstrated large modehop free tuning of an externalcavity diode laser with an offtheshelf laser diode. But that under some external influence, a specific current or temperature, another mode suddenly takes over all the optical power and, for a short while, there may be modehopping or even power in both modes. An external cavity has been developed for use with commercial diode lasers. External cavity laser diodes fibrecoupled laser diodes. Developing an electronically controlled external cavity diode. The use of frequencydependence reflection for the external cavity e. We present a new generation of homebuilt external cavity diode lasers ecdl with improved.
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