High repetition-rate wavelength tuning of an extended cavity diode laser for gas phase sensing

A method for rapid wavelength tuning of an extended cavity diode laser (ECDL) is presented providing for high resolution, narrow bandwidth output over limited spectral regions. The method permits tuning over isolated spectroscopic features at repetition rates of tens of kHz, greatly exceeding conventional ECDL tuning speeds. In this paper we present high repetition rate laser induced fluorescence (LIF) spectroscopy of the 5²P_1/2 to 6²S_1/2 transition in indium at 410 nm, to demonstrate the technique. The presented ECDL design is very easy to implement, cheap and robust, as it employs no moving parts and can be used over all wavelength regions where FP diode lasers are available. This extends the usefulness of standard FP diode lasers to high speed sensing applications. Advantages and disadvantages of the technique are discussed. PACS 42.55.Px; 42.60.Fc; 42.62.Fi; 32.50.+d     

Stable Narrow Linewidth 689nm Diode Laser for the Second Stage Cooling and Trapping of Strontium Atoms

We report stable narrow linewidth laser systems based on self-developed Littman configuration external cavity diode lasers （ECDLs）. The frequency of the ECDL is stabilized to a high fineness ultralow-expansion glass reference cavity with the Pound-Drever-Hall technique. By heterodyne beating of two identical systems, we conclude that the linewidth 4.3× 10^-14 at an averaging measurement time. of each ECDL is reduced to lower than 150 Hz and its frequency stability reaches time of 1 s, the averaged long-term frequency drift is less than 0.2 Hz/s over 30 h     

Self-adaptive, narrowband tuning of a pulsed optical parametric oscillator and a continuous-wave diode laser via phase-conjugate photorefractive cavity reflectors: verification by high-resolution spectroscopy

A dynamic self-adaptive Bragg grating formed in a photorefractive crystal is shown to be a convenient way to attain single-longitudinal-mode (SLM) operation and narrowband tuning both in a pulsed, injection-seeded optical parametric oscillator (OPO) and in a continuous-wave (cw) extended-cavity diode laser. The pulsed OPO cavity comprises a Rh:BaTiO₃ photorefractive (PR) crystal, a periodically poled KTiOPO₄ nonlinear-optical crystal, and a dielectrically-coated end mirror. A continuous-wave seed beam at 820–850 nm from a tunable SLM diode laser traverses firstly the Rh:BaTiO₃ crystal and then is retro-reflected by the end mirror; this creates a wavelength-selective Bragg grating reflector in the PR crystal, thereby completing the OPO cavity. The cavity stays automatically resonant with the seed radiation, with no need to actively control its length or to make any other mechanical adjustment. One form of injection seeder comprises a novel extended-cavity diode laser (ECDL) design incorporating a self-pumped photorefractive phase-conjugate reflector and a compact, high-finesse tunable intracavity ring filter. This combination facilitates robust tunable single-frequency operation with narrow optical bandwidth. The performance characteristics of the OPO and the ECDL are evaluated by recording high-resolution atomic and molecular spectra. Notably, fluorescence-detected sub-Doppler two-photon excitation at 822 nm, of the 8S ←6S transition in atomic Cs, provides a crucial linewidth test.     

A 657-nm narrow bandwidth interference filter-stabilized diode laser

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.     

Frequency-stabilized high-power violet laser diode with an ytterbium hollow-cathode lamp

We have demonstrated in an ytterbium laser cooling and trapping experiment a high-power violet extendedcavity diode laser (ECDL) stabilized to the Yb resonant transition at 398.9 nm in an Yb hollow-cathode lamp. A frequency-dispersion signal, which we obtained by applying a modulation-free dichroic-atomic-vapor laser lock technique, allowed us to stabilize the violet ECDL at a frequency stability below 1 MHz at 1-s average time and a useful output power of 15 mW.     

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 780.247 nm, with a mode-hop-free tuning range of 16 GHz and 9.6 GHz with and without feed-forward on the diode injection current. The measured linewidth was 850 kHz in 500 s, qualified for laser cooling experiments.     

A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb

This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of ¹²⁷I₂. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.     

Preliminary frequency measurement of the electric quadrupole transition in a single laser-cooled 40Ca+ ion

The trapping and laser cooling of ⁴⁰Ca⁺ ion on the way toward optical frequency standards have been developed. A single ⁴⁰Ca⁺ ion is trapped in the miniature Paul trap and laser cooled by two frequency-stabilized diode lasers. A commercial Ti:Sapphire laser system at 729 nm is referenced to a high-finesse cavity to meet the requirements of ultra narrow linewidth of the 4s²S_1/2-3d²D_5/2 electric quadrupole transition. Its center frequency is preliminarily measured to be 411 042 129 686.1 (2.6) kHz. The attempt to finally lock the 729-nm laser system to atomic transition is made. Further work to improve the accuracy of measurement and the stabilization of system locking is in consideration and preparation.     

A diode laser system for spectroscopy of the ultranarrow transition in ytterbium atoms

A narrow-line diode laser system has been developed for high-resolution spectroscopy of the magnetic quadrupole transition in ytterbium (Yb) atoms at 507 nm. The system consists of an extended-cavity laser diode at 1014 nm, a tapered amplifier and a periodically poled lithium niobate nonlinear crystal which converts the wavelength from 1014 nm to 507 nm. We have stabilized the laser frequency and reduced the linewidth below 1 kHz by tightly locking the laser to a high-finesse optical cavity. By using the developed laser system, we have successfully observed the ultranarrow transition in Yb atoms. Furthermore, our simple and compact laser system could be a high performance and portable frequency reference using iodine spectra whose linewidth becomes less than 50 kHz around 507 nm. We have also demonstrated spectroscopy of iodine molecules. PACS 32.30.-r; 07.60.-j     

Preliminary frequency measurement of the electric quadrupole transition in a single laser-cooled 40Ca+ ion

The trapping and laser cooling of ⁴⁰Ca⁺ ion on the way toward optical frequency standards have been developed. A single ⁴⁰Ca⁺ ion is trapped in the miniature Paul trap and laser cooled by two frequency-stabilized diode lasers. A commercial Ti:Sapphire laser system at 729 nm is referenced to a high-finesse cavity to meet the requirements of ultra narrow linewidth of the 4s²S_1/2-3d²D_5/2 electric quadrupole transition. Its center frequency is preliminarily measured to be 411 042 129 686.1 (2.6) kHz. The attempt to finally lock the 729-nm laser system to atomic transition is made. Further work to improve the accuracy of measurement and the stabilization of system locking is in consideration and preparation.      

Single-frequency polarized eye-safe all-fiber laser with peak power over kilowatt

An all-fiber, single-frequency, linearly polarized, high peak-power, pulsed laser at 1,540 nm for Doppler wind lidar is presented. This laser is composed of a single-frequency, narrow-linewidth external cavity diode laser, and multistage fiber amplifiers. A peak power of 1.08 kW and a pulse width of 500 ns at 10 kHz repetition rate are achieved, which is the highest peak power with a linewidth of 800 kHz in erbium-doped silica fiber to our knowledge. The beam quality of M ² < 1.3 and a polarization extinction ratio over 16 dB are obtained. This laser will be employed in a compact long-range coherent Doppler wind lidar.     

CO concentration and temperature measurements in a shock tube for Martian mixtures by coupling OES and TDLAS

CO concentration and gas temperature distribution are diagnosed behind a strong shock wave simulating the Martian atmosphere entry processes by coupling optical emission spectroscopy (OES) and tunable diode laser absorption spectroscopy (TDLAS). The strong shock wave (6.31 ± 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. Temperature of the shock-heated gas is inferred through a precise analysis of the high temporal and spatial resolution experimental spectral of CN violet system (B ² Σ ⁺ →X ² Σ ⁺, Δv = 0 sequence) using OES. A CO absorption line near 2,335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode with 50 kHz repetition rate. Combined with temperature results from OES, CO concentration in the thermal equilibrium region is derived. The current experimental results are complementary for determining an accurate rate coefficient of CO₂ dissociation and validation relevant chemical kinetics models in Mars atmosphere entry processes.     

External cavity diode laser with kilohertz linewidth by a monolithic folded Fabry-Perot cavity optical feedback

We present a extended-cavity diode laser (ECDL) with kilohertz linewidth by optical feedback from a monolithic folded Fabry-Perot cavity (MFC). In our experiments, an MFC replaces the retroreflecting mirror in the traditional ECDL configuration. Beat-note measurements between this MFC-ECDL and a narrow-linewidth reference laser are performed and demonstrate that the linewidth of this MFC-ECDL is about 6.8 kHz. Phase locking of this MFC-ECDL to the reference laser is achieved with a unity gain as small as 10.2 kHz.     

利用自相位延迟方法测量单块腔反馈半导体外腔激光器的线宽

提出了采用单块折叠法布里-珀罗(F-P)腔作为外腔反馈元件实现窄线宽半导体激光器,采用单块腔的光学反馈来锁定外腔激光器,使用自相位延迟法测量该窄线宽激光器的线宽。实验结果表明,激光器线宽小于35kHz。实验还观测到由于单块腔耦合面上各耦合点的几何量和物理量误差不一样,随着折叠面兼输入输出耦合面上的耦合点的变化,外腔激光器的线宽发生改变。     

Sub-ppb NO2 detection by optical feedback cavity-enhanced absorption spectroscopy with a blue diode laser

We report preliminary results on the first application of optical feedback cavity-enhanced absorption spectroscopy with a blue (411 nm) extended cavity diode laser (ECDL) for NO₂ detection. While this technique was originally developed to operate with distributed feedback diode lasers in the near infrared, it is here extended to ECDLs and applied to the blue spectral region. With a simple and compact optical setup, we demonstrate from the baseline noise a minimum detectable NO₂ concentration of 6×10⁹ molecules/cm³ for a single laser scan (70 ms), which extrapolated under atmospheric conditions corresponds to 200 pptv. Signal averaging should allow further lowering of this limit. Observed absorption spectra display more structure than previous spectra obtained at lower resolution by Fourier-transform spectroscopy at the same wavelength. PACS 07.88.+y; 42.55.Px; 42.62.Fi     

基于自制超稳定F-P腔压窄632.8nm外腔半导体激光线宽的实验研究

窄线宽激光由于其具有单色性好、稳定度高、相干长度长等优点,广泛应用于光电检测领域,包括相干通信、精密测量、光学频率标准、吸收光谱计量以及光与物质相互作用研究等.目前频率稳定的氦氖激光器线宽可以达到M Hz量级,分布反馈式(DFB)光纤激光器线宽可达kHz量级,DFB半导体激光器线宽可以达到M Hz量级,然而光栅反馈半导...     

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter

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 k Hz. 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.     

Nonlinear beam clean-up using resonantly enhanced sum-frequency mixing

We investigate the possibility of improving the beam quality and obtaining high conversion efficiency in nonlinear sum-frequency generation. A 765 nm beam from an external cavity tapered diode laser is single-passed through a nonlinear crystal situated in the high intracavity field of a 1342 nm Nd:YVO₄ laser, generating a SFG beam at 488 nm. The ECDL have M _H ² =1.9 and M _V ² =2.4 and the solid-state laser has M ²<1.05. Varying the focusing of the 765 nm beam, the conversion efficiency and the beam quality of the generated 488 nm beam change correspondingly. We show that it is possible to improve the M ² of the 488 nm beam to less than 1.3 while preserving a high conversion efficiency of the SFG process.     

Growth and properties of KLu(WO4)2, and novel ytterbium and thulium lasers based on this monoclinic crystalline host

High‐quality crystals of monoclinic KLu(WO₄)₂, shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb³⁺‐ and Tm³⁺‐doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo‐mechanical, and optical properties, the Yb³⁺ and Tm³⁺ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous‐wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two‐mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q‐switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 μJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode‐locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth‐limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode‐pumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.