A new setup for efficient blue light generation that consists of two passively coupled optical resonators is presented. The
first resonator is based on a broad area laser diode (BAL) in a Littrow external cavity with a special off-axis design. This
external cavity diode laser provides more than 450 mW diffraction limited and narrow bandwidth emission at 976 nm. A
compact cavity design with 40 mm length could be realized. The second resonator is a monolithic high finesse ring
cavity containing a 10 mm bulk periodically poled lithium niobate (PPLN) crystal for resonant second harmonic
generation. This ring resonator consists of four small mirrors with appropriate reflectivities and two GRIN lenses for
stability reasons. All parts of this ring cavity are mounted monolithically on a glass substrate with a size of 19.5 mm x
8.5 mm. First experiments showed good passive matching of both cavities without any active closed-loop control. With
this setup efficient SHG was achieved. A maximum optical output power of 70 mW blue light at 488 nm was obtained.
The conversion efficiency was better than 15%.
Coherent cw-THz-radiation allows access to new applications in the field of medicine, industrial process control, data
communication and security applications. Major advantages of radiation in this spectral range are that it penetrates
through e.g. plastics but is strongly reflected by metals and that molecules show distinct and distinguishable spectra so
that a selective sensing of single species is possible. However, existing THz-sources are either very bulky or expensive.
THz sources can require cryogenic temperatures or emit only low power radiation. Furthermore the setup is often very
complicated and sensitive so that field measurements are not possible.
Generation of THz radiation based on the technology of frequency mixing requires laser radiation with a difference
frequency in the order of 0.1-2 THz. Due to the low efficiency of frequency mixers, high optical power is required for
pumping frequency mixers. Furthermore, the small efficiency requires short optical pulses for avoiding a high heat
dissipation of the frequency mixers.
We investigated an ultra stable 1W two colour THz pump source for the generation of a THz beat signal with rapid
single mode tuning over several THz. The system consist of a fixed wavelength and a motorized tuneable laser pump
sources which are optical amplified within a pulse operation module. One laser is stabilized to an atomic reference while
the other is locked to an optical cavity which can be tuned continuously.
This signal is pump source for a state of the art frequency mixer, which is typically realized as LT-GaAs crystal with an
antenna design.
The combination of high power, small linewidth and fast tunability is essential for many fields in high resolution spectroscopy. External cavity laser diode systems are limited in tuning speed to several kHz by the resonance frequency of the mechanical assembly together with the actuator. We report on the application of a directly modulated DFB laser as master laser within a master laser power amplifier (MOPA) configuration. This DFB MOPA system combines fast frequency tuning up to more then 100kHz tuning speed, a tuning amplitude of more than 10GHz, a narrow linewidth below 5MHz with high output power of 1500mW and an almost Gaussian shaped beam quality (M2<1.2). The coupling efficiency to optical waveguides as well as single mode fibers exceeds 60%. This concept can be realized within the wavelength regime between 730 and 1060nm. We approved this light source for high resolution spectroscopy by frequency locking to the saturated Rubidium absorption at 780nm. Applying two DFB lasers as master lasers of the MOPA configuration opens the choice to high frequency modulated THz radiation.
High resolution spectroscopy of environmental and medical gases requires reliable, fast tunable laser light sources in the mid-infrared (MIR) wavelength regime between 3 and 5 μm. Since this wavelength cannot be reached via direct emitting room temperature semiconductor lasers, additional techniques like difference frequency generation (DFG) are essential. Tunable difference frequency generation relies on high power, small linewidth, fast tunable, robust laser diode sources. We report a new, very compact, alignment insensitive, robust, external cavity diode laser system in Littman/Metcalf configuration with an output power of 1000 mW and an almost Gaussian shaped beam quality (M2<1.2). The coupling efficiency for optical waveguides as well as single mode fibers exceeds 70%. The center wavelength is widely tunable within the tuning range of 20 nm via remote control. This laser system operates longitudinally single mode with a mode-hop free tuning range of up to 150 GHz without current compensation and a side-mode-suppression better than 50 dB. This concept can be realized within the wavelength regime between 750 and 1060 nm. We investigated this light source for high resolution spectroscopy in the field of Cavity Ring-Down Spectroscopy (CRDS). Our high powered Littman/Metcalf laser system was part of a MIR-light source which utilizes difference-frequency generation in Periodically Poled Lithium Niobate (PPLN) crystals. At the wavelength of 3.3 μm we were able to achieve a high-resolution absorption spectrum of water with four resolved isotopic H2O components. This application clearly demonstrates the suitability of this laser for high-precision measurements.
KEYWORDS: Semiconductor lasers, High power lasers, Laser systems engineering, Absorption, Spectroscopy, Chemical species, Diodes, Light sources, High power diode lasers, Resonators
The combination of high power, small linewidth and rapid tuneability is essential for many fields in high resolution spectroscopy. Furthermore these optical features are essential for laser-cooling techniques. Enhancement of high power lasers with excellent spectral and spatial quality is currently an important research subject. The requirements for a laser system applied in both fields of application are demanding: a mode-hop free tuning range of a few GHz, with a linewidth in the order of 1MHz and an output power of a few 100mW. We report a very compact external cavity diode laser system (ECDL) with an output power of up to 800mW with an almost Gaussian shaped beam quality (M2<1.2). The coupling efficiency for a single mode fibre exceeds 60%. The centre wavelength can be preadjusted within the tuning range of 20 nm. This laser operates single mode with a mode-hop free tuning range of up to 15GHz without current compensation and a side-mode-suppression better than 50dB at different wavelength between 730 and 1060nm.
To demonstrate the suitability for neutral atom cooling we used this laser as light source in the production of a BEC of over a million 87Rb atoms. In addition we approved this light source for high resolution spectroscopy, more precisely for the Cavity-Ring-Down-Spectroscopy (CRDS). Our ECDL was part of a MIR-light source which utilizes difference-frequency-generation in PPLN. At the wavelength of 3.3μm we were able to perform a high resolution absorption measurement of 50ppb Ethane. Both applications clearly demonstrate the suitability of this laser for high-precision measurements.
KEYWORDS: High power lasers, Chemical species, Semiconductor lasers, Laser systems engineering, Modulation, Rubidium, Tunable lasers, Single mode fibers, Laser stabilization, Diodes
Since the introduction of laser-cooling techniques for neutral atoms, the enhancement of high-power lasers with excellent spectral and spatial quality has been an important research subject. We report a new principle of using high-power laserdiodes directly in an external cavity. The very compact design offers an output power of up to 1 W and an excellent beam quality (M2 < 1.2). The coupling efficiency for a single mode fiber exceeds 60%. The center wavelength can be tuned between 775 nm and 785 nm. This laser operates single mode with a mode-hop free tuning range of up to 15 GHz without current modulation and a side-mode suppression better than 55 dB. Demonstrating the suitability for neutral atom cooling we used this laser as light source in the production of a BEC of over a million 87Rb atoms.
We report on our recent advances with cavity ring-down spectroscopy using mid-infrared cw lasers. An external high- finesse cavity is excited on a single fundamental mode with a tunable laser operating in the 3 micrometers region. After excitation the laser power is turned off for a short time and the subsequent decay of the field stored inside the cavity is observed. The effective pathlength covered by the laser light inside the cavity during the decay amounts to several km, depending on the mirror reflectivity. Measurement of the decay time gives the photon losses and thus enables the detection of weakly absorbing species inside the cavity. This approach is closely related to cavity ring-down spectroscopy with pulsed lasers. However the cw approach exhibits several advantages concerning spectral resolution and detection sensitivity. Application of this method to online monitoring of trace gases seems to be very promising. We demonstrate detection of hydrocarbons, like membrane and ethylene on the ppb level.
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