Tunable high-power narrow-spectrum external-cavity diode laser at 675 nm as a pump source for UV generation

High-power narrow-spectrum diode laser systems based on tapered gain media in an external cavity are demonstrated at 675 nm. Two 2 mm long amplifiers are used, one with a 500 μm long ridge-waveguide section (device A), the other with a 750 μm long ridge-waveguide section (device B). Laser system A based on device A is tunable from 663 to 684 nm with output power higher than 0.55 W in the tuning range; as high as 1.25 W output power is obtained at 675.34 nm. The emission spectral bandwidth is less than 0.05 nm throughout the tuning range, and the beam quality factor M(2) is 2.07 at an output power of 1.0 W. Laser system B based on device B is tunable from 666 to 685 nm. As high as 1.05 W output power is obtained around 675.67 nm. The emission spectral bandwidth is less than 0.07 nm throughout the tuning range, and the beam quality factor M(2) is 1.13 at an output power of 0.93 W. Laser system B is used as a pump source for the generation of 337.6 nm UV light by single-pass frequency doubling in a bismuth triborate (BIBO) crystal. An output power of 109 μW UV light, corresponding to a conversion efficiency of 0.026% W(-1), is attained.     

Unidirectional single-mode Nd:YAG laser with a planar semimonolithic ring cavity

Unidirectional single-mode operation of a diode-pumped Nd:YAG laser with a planar semimonolithic ring cavity has been demonstrated at 1064 nm. The semimonolithic cavity consists of a laser active medium placed in a magnetic field, a crystal quartz plate, and an output coupling mirror, which form an optical diode by acting as a Faraday rotator, a reciprocal polarization rotator, and a partial polarizer, respectively. A single-mode output power of 155 mW and a slope efficiency of 17% were obtained with a 1.2-W diode laser at 809 nm. A laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems and continuous tuning to greater than 2 GHz was observed.     

Widely Tunable Continuous-Wave CR(3+):LiSrAlF(6) Ring Laser from 800 to 936 nm

We report on a widely tunable, diode-pumped, continuous-wave, single-frequency Cr(3+):LiSrAlF(6) laser with a novel double-ring cavity configuration. The optical diode and the tuning element were located in the ring subcavity to decrease their insertion loss. Using an 1800-lines/mm grating as the tuning element, we obtained a laser emission of 20-mW output power at 870 nm and a tuning range of from 800 to 936 nm. When we used a 1200-lines/mm grating with a higher diffraction efficiency, the laser had a slightly wider tuning range of from 800 to 938 nm. However, the output power decreased at this tuning range.     

Sensitive absorption spectroscopy by use of an asymmetric multiple-quantum-well diode laser in an external cavity

We have developed a broadly tunable diode laser system by employing custom-designed asymmetric multiple-quantum-well (AMQW) InGaAsP lasers in an external cavity configuration. Feedback is provided by a diffractive optical element with high coupling efficiency and wavelength selectivity, allowing for single-mode tuning of the output wavelength by varying the external cavity length. This tunable laser system was used experimentally to perform absorption spectroscopy on weak CO(2) lines over a broad wavelength region in the near infrared. An experimental tuning range of 80 nm has been observed for a laser cavity length of 600 mum, which is double the tuning range found with conventional, uncoated quantum-well lasers. We achieved a detection sensitivity of 5 x 10(-6) at 95% confidence over the wavelength range of 1.54-1.62 mum by employing a second-harmonic detection technique. The theoretical predictions of a broad gain profile from an ambipolar rate equation model are found to correspond to the experimentally observed increased tunability of the uncoated AMQW lasers.     

Extending the continuous tuning range of an external-cavity diode laser

The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.     

Compact and Efficient 3.2-W Diode-Pumped Nd:YVO(4)/KTP Green Laser

We demonstrate a simple way to achieve single-frequency operation by using fiber-coupled diode-pumped Nd:YVO(4)/KTP green lasers in a short standing-wave linear cavity. A single-mode output with 3.2-W green power was generated with a 12.6-W pump power corresponding to a conversion efficiency of 25.4%. The single-mode operation was obtained through the combined action of the anisotropic emission cross section of Nd:YVO(4) and the KTP crystal acting as a birefringent filter.     

Innovative design of a tunable laser using liquid crystal tuning elements

An innovative non-mechanical and low power consumption tunable external cavity laser (ECL) using liquid crystal tuning elements is proposed. This contains a gain chip, a collimating lens, tuning elements and a partial-reflection mirror. The proposed tunable ECL can achieve both coarse tuning and fine tuning, and it is designed to lase at wavelength matching the International Telecommunication Union (ITU) channels, which is one of the important requirements in optical communication. The tuning elements include an ITU etalon, a liquid crystal Fabry–Pérot interferometer (LC-FPI) and a fine tuner. Only two parameters are required to tune the wavelength over the whole C-band, namely the voltage over the LC-FPI and the fine tuner. This high reliability cost-effective design proposes a theoretical tuning range of about 80?nm. The LC tuning elements including LC-FPI and fine tuner has been fabricated and tested.     

Discretely tunable single-mode lasers on GaSb using two-dimensional photonic crystal intracavity mirrors

We report on single-mode emitting coupled cavity ridge waveguide lasers on the GaSb material system in the 2?μm spectral range using two-dimensional (2D) photonic crystals (PhCs). Eight rows of 2D PhCs lateral to the ridge waveguides act as intermediate mirrors and are used to create two coupled cavities. This leads to preferential emission at one single longitudinal mode in the emission spectrum with side mode suppression ratios of 30-35?dB. Monolithic integration of high reflectivity 2D PhC back mirrors allows the realization of cavity lengths as short as 300?μm with threshold currents as low as 18.5?mA while reaching output powers well above 18?mW. Under variation of driving current the lasers exhibit both discrete and continuous tuning behavior over a wide current range very well explicable by simulation of the sub-threshold spectra, rendering the devices especially interesting for multi-gas sensing by absorption spectroscopy.     

Highly integrated coupled cavity photonic crystal laser with on-chip power control on the AlGaIn/AsSb material system

We present a multi-segment photonic crystal coupled cavity laser device on GaSb with a microstructured internal photodiode. This monolithically integrated power monitor is added as a third segment to a coupled cavity laser and is separated from the active device by six rows of two-dimensional photonic crystals, acting as highly reflecting mirrors. There is no additional fabrication step needed to integrate this feature into the coupled cavity laser, resulting in a highly integrated laser device of only 800?μm length. The device with lasing wavelength around 1955?nm shows single mode emission over a tuning range of as large as 16?nm and exhibits output powers of up to 9?mW.     

Single-mode diode laser with a large frequency-scanning range based on weak grating feedback

A single-mode GaAlAs diode laser with over 90% output-coupling power and a large frequency-scanning range is reported. Based on grating feedback in the Littrow configuration, it is demonstrated that, with weak feedback (1.5 × 10(-3) in this experiment), over a 7.5-GHz continuous tuning range can be achieved around tuning gaps of free-running operation. A frequency self-locking effect is also demonstrated in this system.     

Technique for continuous tuning of optical fiber lasers

For the first time to the authors' knowledge, we have demonstrated how thermally controlled overcoupled fused fiber couplers and fiber loop mirrors based on these couplers can be used as broadband tuning elements in a fiber laser cavity. No bulk optical elements play any role in this technique. Temperature tuning the coupler results in a shift in the coupling ratio or in the effective output coupler transmission. For a fixed pump source, and for a given laser cavity, this shift causes the lasing wavelength to shift. We have continuously tuned an Er silica fiber laser in this manner over the range of 1527-1570 nm in a ring configuration, and, using a fiber loop mirror with these couplers in a linear Tm silica fiber laser cavity, we have achieved more than 50-nm broadband tuning over the range of 1850-1910 nm. The tuning range and the sensitivity to temperature depend on the degree of overcoupling of the loop mirror coupler.     

单模太赫兹半导体激光器高精度调谐特性研究

大量物质的特征吸收谱在太赫兹范围内,因此近年来太赫兹光谱应用的发展备受关注。相比于现有的商业光谱仪,基于可调谐单模激光器的光谱测量方法具有高精度和高光谱获取速度的优势。太赫兹量子级联激光器是可调谐激光源的理想选择。在利用其实现光谱测量前,需对其调谐特性进行研究,但是现有测量方法受到精度限制。研究发现,利用太赫兹量子级联光频梳和单模激光器之间的拍频,可在微波波段得到对应的拍频信号。当调谐单模激光器时,拍频信号会发生相应的频移。因此,结合量子级联激光器的自探测,利用频谱分析仪测量拍频信号的频移情况,可以实现对单模激光器调谐的高精度测量。最终得到所测太赫兹单模激光器的调谐速率为53 MHz/K（温度调谐）和2.7 MHz/mA（电流调谐）。     

Writing and probing light-induced waveguides thanks to an endlessly single-mode photonic crystal fiber

We demonstrate writing and probing of light-induced waveguides in photorefractive bulk LiNbO3 crystal using an endlessly single-mode photonic crystal fiber. The optical waveguides are written at visible wavelengths by slightly raising the ferroelectric crystal temperature to benefit from the pyroelectric-driven photorefractive effect and the guiding properties are investigated at telecom wavelengths using the same photonic crystal fiber. End butt coupling with this photonic crystal fiber enables writing and probing of optical waveguides due to the self-alignment properties of spatial solitons.     

Antireflection-coated blue GaN laser diodes in an external cavity and Doppler-free indium absorption spectroscopy

Commercially available GaN-based laser diodes were antireflection coated in our laboratory and operated in an external cavity in a Littrow configuration. A total tuning range of typically 4 nm and an optical output power of up to 30 mW were observed after optimization of the external cavity. The linewidth was measured with a beterodyne technique, and 0.8 MHz at a sweep time of 50 ms was obtained. The mode-hop-free tuning range was more than 50 GHz. We demonstrated the performance of the laser by detecting the saturated absorption spectrum of atomic indium at 410 nm, allowing observation of well-resolved Lamb dips.     

Wavelength-shift speckle interferometry for absolute profilometry using a mode-hop free external cavity diode laser

Abstract

In this paper we present an absolute surface topography measurement with a tuneable diode laser with an external cavity that has a tuning range of as much as 25 nm without mode hops and a very high tuning speed of less than 1 s for the whole range. With this laser, an absolute wavelength-shift speckle pattern interferometer was realized, capable of measuring optically smooth and rough surfaces. We briefly explain the principles of operation, and the importance of wavelength tuning without mode hops. We discuss the capabilities, possible measuring ranges and some results as well as calibration methods of wavelength-shift speckle profilometry.     

基于光折变光栅的可调谐滤波方案及特性分析

在LiNbO3单模波导上利用双光束干涉可形成光折变波导光栅,针对粗波分复用系统提出了通过实时改变双光束之间的夹角进而改变光栅间距,实现可调谐滤波的方案.利用光折变动力学理论,得到光栅调谐时间在毫秒数量级.研究发现,适当提高光强和增加杂质掺杂浓度可提高衍射效率、减少光栅初次建立时间.基于耦合波理论的数值模拟结果表明,增大光栅长度能使衍射效率提高且带宽变小,而增加折射率调制度使衍射效率提高但同时带宽变宽.在折射率调制度为8×10-5,光栅长度大于12mm时,可获得91％以上的衍射效率和小于0.08 nm的带宽.     

Broadband Tuning of a Continuous-Wave, Doubly Resonant, Lithium Triborate Optical Parametric Oscillator from 791 to 1620 nm

We report the use of extreme broadband, high reflectivity >99.5%, optical parametric oscillator (OPO) cavity mirrors. A continuous-wave, doubly resonant, OPO demonstrated tuning over a range of 791-1620 nm with a single mirror set. Wavelength tuning was performed by temperature tuning the nonlinear material of lithium triborate. Narrow linewidth oscillation was confirmed throughout the tuning range, and threshold pump power increased gradually from 50 mW near the degeneracy to 800 mW at the tuning band edge in a double-pass pumping configuration.     

Increasing the output of a Littman-type laser by use of an intracavity Faraday rotator

We present a method of external-cavity diode-laser grating stabilization that combines the high output power of the Littrow design with the fixed output pointing of the Littman-Metcalf design. Our new approach utilizes a Faraday-effect optical isolator inside the external cavity. Experimental testing and a model that describes the tuning range and optimal tuning parameters of the laser are described. Preliminary testing of this design has resulted in a short-term linewidth of 360 KHz and a side-mode suppression of 37 dB. The laser tunes mode hop free over 7 GHz, and we predict that much larger tuning ranges are possible.     

Performance characteristics of external cavities to generate deep-ultraviolet coherent lights resonant to 3p3P14s3P0 cyclic transition of 28Si

Abstract

We developed a robust 252 nm single-mode coherent continuous-wave light source through two-stage highly efficient frequency conversion systems using external cavities. In the first stage, we obtained the second harmonics (SH) power of 630 mW from the LBO-installed external cavity by frequency doubling of a 746 nm Ti: sapphire laser with an efficiency of almost 50% [Y. Asakawa, H. Kumagai, K. Midorikawa, M. Obara, Opt. Commun. 217 (2003) 311.]. In the second stage, 252 nm light power was obtained by doubly resonant sum-frequency mixing of 373 nm light from the first-stage conversion system and 780 nm light from another Ti:sapphire laser. In the sum-frequency external cavity, the maximum 252 nm light power of over 150 mW is obtained, which is about three times larger than that obtained in our previous experiment.     

Performance characteristics of external cavities to generate deep-ultraviolet coherent lights resonant to 3pP1−4sP0 cyclic transition of Si

We developed a robust 252 nm single-mode coherent continuous-wave light source through two-stage highly efficient frequency conversion systems using external cavities. In the first stage, we obtained the second harmonics (SH) power of 630 mW from the LBO-installed external cavity by frequency doubling of a 746 nm Ti: sapphire laser with an efficiency of almost 50% [Y. Asakawa, H. Kumagai, K. Midorikawa, M. Obara, Opt. Commun. 217 (2003) 311.]. In the second stage, 252 nm light power was obtained by doubly resonant sum-frequency mixing of 373 nm light from the first-stage conversion system and 780 nm light from another Ti:sapphire laser. In the sum-frequency external cavity, the maximum 252 nm light power of over 150 mW is obtained, which is about three times larger than that obtained in our previous experiment.