External Cavity Diode Laser System Research Articles

Wideband current modulation of diode lasers for frequency stabilization.

We present a current modulation technique for diode laser systems, which is specifically designed for high-bandwidth laser frequency stabilization and wideband frequency modulation with a flat transfer function. It consists of a dedicated current source and an impedance matching circuit both placed close to the laser diode. The transfer behavior of the system is analyzed under realistic conditions employing an external cavity diode laser (ECDL) system. We achieve a phase lag smaller than 90° up to 25 MHz and a gain flatness of ±3 dB in the frequency range of DC to 100 MHz, while the passive stability of the laser system is not impaired. The potential of the current modulation scheme is demonstrated in an optical phase-locked loop between two ECDL systems with a phase noise of 42 mradrms. The design files are available as an open-source project.

High-power external cavity diode laser with narrow linewidth emission and adjustable polarization state at 445 nm

A high-power external cavity diode laser (ECDL) system at 445 nm is proposed that has narrow-band linewidth emission and adjustable polarization state and can be used for nonlinear frequency conversion in deep ultraviolet spectrum. By introducing a half-wave plate to control the polarization state of the laser source, the first-order diffraction (R1st) efficiency is changed. The relationship between the linewidth and the first-order diffraction efficiency is discussed through simulation and experiment. In addition, the tunable ranges of the ECDL are measured. Finally, a continuous-wave output with the spectral width of 72 pm at 445 nm and a maximum optical output power of 1.52 W can be obtained when R1st is 25%, of which the tunable range has a minimum of 2.3 nm.

A PLATFORM FOR ULTRA-COLD EXTERNAL CAVITY DIODE LASERS

We report on the construction of a platform for ultra-cold tuneable external cavity diode laser system working well below the room temperature (-75 0C) under rough vacuum (28mBar). A theoretical procedure is also presented to calculate thermal control parameters including heat transfer rate, thermal isolation and heat dissipation of the system. Temperature tuning capability of the system was examined utilizing a 658nm (AlGaInP) single mode laser diode. With the system designed the temperature dependent tuning range was expended to almost two fold while halving the bandwidth regarding to its room temperature performances.

3D printing an external-cavity diode laser housing

The ability to control the frequency of an external-cavity diode laser (ECDL) is an essential component for undergraduate laboratories and atomic physics research. Typically, the housing for the ECDL's diffraction grating and piezoelectric transducer is either purchased commercially or machined from metal. Here, we present an alternative to these commonly used options that utilizes 3D printing, a tool available in many physics departments. We characterize the performance of our ECDL system using atomic spectroscopy and self-heterodyne interferometry and show that it is sufficient for use in undergraduate spectroscopy experiments and a number of research applications, where extremely narrow laser linewidths are not necessary. The performance and affordability of 3D-printed designs make them an appealing option for future use.

Blue Laser Diode System With an Enhanced Wavelength Tuning Range

A prism-based self-injection locked seamlessly tunable blue InGaN/GaN laser diode composite cavity system is presented. A rigorous analysis of this external cavity diode laser (ECDL) system is performed at two different optical feedback powers. At 130 mA low injection, the high reflection system (HRS) exhibits a record wideband tuning span of ∼12.11 nm with a side-mode-suppression-ratio (SMSR) ≥ 15 dB, measuring as high as 40 dB, linewidth ≤110 pm, and a working power of about 3 mW. Whereas, a tuning range of 8 nm with linewidth ≤88 pm, SMSR ≥ 13 dB, reaching a maximum of 35 dB with 14.5 mW usable power is achieved from the low reflection system (LRS) at the same injection current. Moreover, an inverse relationship between the optical power and the tunability is observed in both the systems with a value as high as 180 mW exhibited by LRS configuration and attaining a tunability of 4.5 nm. Both systems highlight high stability even at higher injection currents and temperature. Such a robust, simple, and compact system may serve as a crucial light source in a plethora of diverse applications besides visible optical communications. To the best of our knowledge, this is the first report on a continuously tunable self-injection locked tunable laser system.

Dynamics of a green high-power tunable external-cavity broad-area GaN diode laser

Although external-cavity feedback with a grating is widely used to achieve a tunable high-power narrow-linewidth broad-area diode laser (BAL) system, the dynamics of such a system is seldom studied. In this paper, the temporal dynamics of a tunable high-power green external-cavity diode laser system based on a GaN BAL and Littrow external-cavity is investigated experimentally. The regular pulse package oscillation (PPO) is observed just above the threshold. The oscillating period of the pulse package decreases with the increasing injected current. As the current increases further, the pulse package oscillates irregularly, and finally changes to a chaotic state. The PPO is observed, for the first time to our knowledge, in a BAL with an external-cavity grating feedback.

500 mW tunable external cavity diode laser with narrow line-width emission in blue-violet region

A tunable external cavity diode laser (ECDL) system with narrow line-width emission at 410nm is presented. Based on a commercially available laser diode and a Littrow arranged reflective holographic grating, a maximum output power over 500mW with line-width of about 50pm is achieved at the rated current. The power efficiency is over 85% and the threshold decreases over 20% compared to the free-running laser diode. Manual tuning range over 5nm is achieved around threshold condition and over 2nm at high injection currents up to 500mA with side mode suppression ratio larger than 20dB.

A low-temperature external cavity diode laser for broad wavelength tuning.

We report on the design and characterization of a low-temperature external cavity diode laser (ECDL) system for broad wavelength tuning. The performance achieved with multiple diode models addresses the scarcity of commercial red laser diodes below 633 nm, which is a wavelength range relevant to the spectroscopy of many molecules and ions. Using a combination of multiple-stage thermoelectric cooling and water cooling, the operating temperature of a laser diode is lowered to -64 °C, more than 85 °C below the ambient temperature. The laser system integrates temperature and diffraction grating feedback tunability for coarse and fine wavelength adjustments, respectively. For two different diode models, single-mode operation is achieved with 38 mW output power at 616.8 nm and 69 mW at 622.6 nm, more than 15 nm below their ambient temperature free-running wavelengths. The ECDL design can be used for diodes of any available wavelength, allowing individual diodes to be tuned continuously over tens of nanometers and extending the wavelength coverage of commercial laser diodes.

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter**Project supported by the National Natural Science Foundation of China (Grant No. 91436210) and the International Science and Technology Cooperation Program of China (Grant No. 2010DFR10900).

We demonstrate an 852-nm external cavity diode laser (ECDL) system whose wavelength is mainly determined by an interference filter instead of other wavelength selective elements. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 28.3 kHz. Moreover, we test the application of the ECDL in the Faraday atomic filter. Besides saturated absorption spectrum, the transmission spectrum of the Faraday atomic filter at 852 nm is measured by using the ECDL. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.

Tuning range and output power optimization of an external-cavity GaN diode laser at 455 nm.

In this paper we discuss how different feedback gratings affect the tuning range and the output power of external feedback diode laser systems. A tunable high-power narrow-spectrum external-cavity diode laser system around 455 nm is investigated. The laser system is based on a high-power GaN diode laser in a Littrow external-cavity. Both a holographic diffraction grating and a ruled diffraction grating are used as feedback elements in the external cavity. The output power, spectral bandwidth, and tunable range of the external cavity diode laser system are measured and compared with the two gratings at different injected currents. When the holographic grating is used, the laser system can be tuned over a range of 1.4 nm with an output power around 530 mW. When the ruled grating is used, the laser system can be tuned over a range of 6.0 nm with an output power around 80 mW. The results can be used as a guide for selecting gratings for external-cavity diode lasers for different requirements.

Single-pass UV generation at 222.5 nm based on high-power GaN external cavity diode laser.

We demonstrate a compact system for single-pass frequency doubling of high-power GaN diode laser radiation. The deep UV laser light at 222.5 nm is generated in a β-BaB2O4 (BBO) crystal. A high-power GaN external cavity diode laser (ECDL) system in Littrow configuration with narrowband emission at 445 nm is used as pump source. At a pump power of 680 mW, a maximum UV power of 16 μW in continuous-wave operation at 222.5 nm is achieved. This concept enables a compact diode laser-based system emitting in the deep ultraviolet spectral range.

400 mW external cavity diode laser with narrowband emission at 445 nm.

A high-power external cavity diode laser (ECDL) system with narrowband emission is presented. The system is based on a commercially available high-power GaN laser diode. For the ECDL, a maximum optical output power of 400 mW in continuous-wave operation with narrowband emission is achieved. Longitudinal mode selection is realized by using a surface diffraction grating in Littrow configuration. A spectral width of 20 pm at 445 nm with a side-mode suppression ratio larger than 40 dB is achieved. This concept enables diode laser systems suitable for subsequent nonlinear frequency conversion into the UV spectral range.

A high-power 626 nm diode laser system for Beryllium ion trapping

We describe a high-power, frequency-tunable, external cavity diode laser system near 626 nm useful for laser cooling of trapped (9)Be(+) ions. A commercial single-mode laser diode with rated power output of 170 mW at 635 nm is cooled to ≈-31°C, and a single longitudinal mode is selected via the Littrow configuration. In our setup, involving two stages of thermoelectric cooling, we are able to obtain ≈130 mW near 626 nm, sufficient for efficient frequency doubling to the required Doppler cooling wavelengths near 313 nm in ionized Beryllium. In order to improve nonlinear frequency conversion efficiency, we achieve larger useful power via injection locking of a slave laser. In this way the entirety of the slave output power is available for frequency doubling, while analysis may be performed on the master output. We believe that this simple laser system addresses a key need in the ion trapping community and dramatically reduces the cost and complexity associated with Beryllium ion trapping experiments.

Precise frequency measurements of iodine hyperfine transitions at 671 nm

We report absolute frequency measurements on the a(1), a(10), and a(15) hyperfine components of the R(78) 4-6 line of (127)I(2). An external-cavity diode laser system at 671 nm is frequency-stabilized to the saturated absorption center obtained by modulation transfer spectroscopy in an iodine vapor cell. Its absolute frequency is measured by an optical frequency comb. The effect of pressure shift is investigated to obtain the absolute transition frequency at zero pressure. Our determination of the line centers reaches a precision of better than 40 kHz and will provide useful input for theoretical calculations. This frequency-stabilized laser can be used as a reference laser for the spectroscopy of lithium D lines.

An external cavity diode laser using a volume holographic grating

This study presents an external cavity diode laser (ECDL) system, utilizing a volume holographic grating (VHG) and a microfabricated silicon flexure as the VHG holder. The laser design is aimed for easy assembly, controllability, and better stability of the laser cavity. The laser frequency was stabilized to a D2 transition of rubidium at 780.247nm, with a mode-hop-free tuning range of 16GHz and 9.6GHz with and without feed-forward on the diode injection current. The measured linewidth was 850kHz in 500s, qualified for laser cooling experiments.

Multi-threshold second-order phase transition in laser

We present a theory of the multi-threshold second-order phase transition, and experimentally demonstrate the multi-threshold secondorder phase transition phenomenon. With carefully selected parameters, in an external cavity diode laser system, we observe secondorder phase transition with multiple (three or four) thresholds in the measured power-current-temperature three dimensional phase diagram. Such controlled death and revival of second-order phase transition sheds new insight into the nature of ubiquitous secondorder phase transition. Our theory and experiment show that the single threshold second-order phase transition is only a special case of the more general multi-threshold second-order phase transition, which is an even richer phenomenon.

Miniaturized Tunable External Cavity Diode Laser with Single-Mode Operation and a Narrow Linewidth at 633 nm

A miniaturized, standalone tunable semiconductor laser module operating at a wavelength of 633 nm with a footprint as small as 10 mm × 5 mm is presented. The module is based on an external cavity diode laser system with no moving parts and features a frequency tuning range of 25 GHz with a spectral linewidth of approximately 10 MHz. An output power of 10 mW within a nearly diffraction-limited beam is demonstrated. The electrical power consumption, including thermal management, is around 0.7 W.

Doppler-free frequency-modulation spectroscopy of atomic erbium in a hollow-cathode discharge cell

The erbium atomic system is a promising candidate for an atomic Bose-Einstein condensate of atoms with a non-vanishing orbital angular momentum ($L \neq 0$) of the electronic ground state. In this paper we report on the frequency stabilization of a blue external cavity diode laser system on the 400.91 $nm$ laser cooling transition of atomic erbium. Doppler-free saturation spectroscopy is applied within a hollow cathode discharge tube to the corresponding electronic transition of several of the erbium isotopes. Using the technique of frequency modulation spectroscopy, a zero-crossing error signal is produced to lock the diode laser frequency on the atomic erbium resonance. The latter is taken as a reference laser to which a second main laser system, used for laser cooling of atomic erbium, is frequency stabilized.

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.

657nm窄带干涉滤波片稳频半导体激光器

We present a 657-nm external cavity diode laser (ECDL) system, where the output frequency is stabilized by a narrow-band high transmission interference filter. This novel diode laser system emits laser with an instantaneous linewidth of 7 kHz and a broadened linewidth of 432 kHz.