Frequency stabilization of a frequency-doubled 197.2 THz distributed feedback diode laser on rubidium 5S1/2→7S1/2 two-photon transitions

A 197.2 THz (1520.2 nm) ITU-T grid distributed feedback (DFB) diode laser is frequency stabilized at 197.198 THz by 1ocking its second harmonic (SH) signal on the rubidium 5S_1/2→7S_1/2 two-photon transition at 394.396 THz (760.1 nm). With 100 mW from the DFB diode laser and amplifying by an erbium-doped fiber amplifier, we obtain an SH power of 15 mW using a periodically poled lithium niobate (PPLN) waveguide frequency doubler. The stability was 2×10⁻¹¹ (10 s), corresponding to a frequency variation of 4 kHz at 1520.2 nm. Our scheme provides a compact and high performance frequency reference in the communication band.     

Compact, Low Threshold Nd^3＋：YVO4 Self-Raman Laser at 1178 nm

A compact low-threshold Raman laser at 1178 nm is experimentally realized by using a diode-end-pumped actively Q-switched Nd^3＋ ：YVO4 self-Raman laser. The threshold is 370mW at a pulse repetition frequency of S kHz. The maximum Raman laser output is 182 m W with the pulse duration smaller than 20 ns at a pulse repetition frequency of 30kHz with 1.8 W incident power. The optical efficiency from the incident power to the Raman laser is 10% and the slope efficiency is 13.5%.     

Dual-wavelength laser operation at 1061 and 942 nm in Nd:GSAG

A dual-wavelength continuous-wave (CW) diode end-pumped gadolinium scandium aluminum garnet (Nd:GSAG) laser that generates simultaneous laser action at the wavelengths 1061 and 942 nm is demonstrated. A total output power of 589 mW (476 mW at 1061 nm and 113 mW at 942 nm) for the dual-wave-length was achieved at the incident pump power of 18.2 W. The M ² values for 942 and 1061 nm lights were found to be around 1.18 and 1.37, respectively.     

All-solid-state CW Nd:GdVO<Subscript>4</Subscript>-LBO red laser under direct 912 nm pumping

We report a red laser at 670.5 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a 1341 nm Nd:GdVO₄ laser under in-band diode pumping at 912 nm. An LBO crystal, cut for critical type I phase matching is used for second harmonic generation of the laser. At an incident pump power of 8.9 W, as high as 347 mW of CW output power at 670.5 nm is achieved. The fluctuation of the red output power was better than 3.7% in the given 30 min, and the beam quality factor M ² is 1.65.     

Resonant photoacoustic detection of trace gas with DFB diode laser

A resonant photoacoustic detection system based on a low-power distributed feedback diode laser is developed. This sensor has been applied to the detection of acetylene (C₂H₂) using a specifically designed photoacoustic cell operating on its second longitudinal mode. The minimum detectable limit of about 10 parts-per-million volume (SNR=1) is achieved with an average laser power of 3.5 mW at atmospheric pressure, and an integration time constant of 3 ms; thus, the minimum detectable absorption coefficient normalised by power and bandwidth is 4.0×10⁻⁸ W cm⁻¹/√Hz. The optimum operating pressure buffered with N₂ is also investigated. The realisation of our system is described and experimental results are compared with different modulation techniques and other results reported in the literature. A number of issues arising from the conventional use of mechanical chopping of the beam can be effectively suppressed in wavelength modulation PA spectroscopy (WM-PAS) and second harmonic detection.     

Efficient laser operation and continuous-wave diode pumping of Cr2+:ZnSe single crystals

Efficient continuous-wave laser operation of Cr²⁺:ZnSe was demonstrated with an output power of 1400 mW at an absorbed pump power of 1900 mW from a Tm:YAG laser. Under continuous-wave diode pumping at 1.54 μm an output power of 15 mW was obtained from a Cr⁺²:ZnSe laser. Excited state absorption is shown to be negligible in the pump and laser spectral region. Received: 12 October 2000 / Published online: 30 November 2000     

All-solid-state Yb:KYW-LBO blue-green laser at 500 nm

It is reported that efficient continuous-wave (CW) blue-green laser generation at 500 nm in a LBO crystal at type-I phase matching direction performed with a Ti:sapphire laser-pumped Yb:KYW laser. With incident pump power of 8.7 W, output power of 138 mW at 500 nm has been obtained using a 10 mm-long LBO crystal. At the output power level of 138 mW, the blue-green output stability is better than 2.8%. The blue-green beam quality M ² values were equal to 1.25 and 1.18 in X and Y directions, respectively.     

用单块激光器和环形外腔获得稳定的532 nm激光

采用单块半非平面Nd:YAG单频环形激光器和环形外腔倍频技术，获得了单频功率249.5mW的532nm波长的绿光输出，倍频效率43.2%，实现了倍频腔与激光器之间的跟踪锁定，倍频光功率稳定性优于1％，理论计算与实验结果一致。     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

Efficient red light generated by intracavity frequency doubling of a 1331 nm Nd:GGG laser with LBO

We report a continuous-wave (CW) coherent red radiation at 666 nm by intracavity frequency doubling generation of 1331 nm Nd:GGG laser. With incident pump power of 18.3 W, output power of 910 mW at 666 nm has been obtained using a 10 mm-long LBO crystal. At the output power level of 910 mW, the output stability is better than 5%. The beam quality M ² values were equal to 1.21 and 1.34 in X and Y directions, respectively.     

A tunable light source in the 370 nm range based on an optically stabilized,frequency-doubled semiconductor laser

A tunable harmonic output power of 18 W at a wavelength of =370 nm is obtained by resonance-enhanced frequency doubling of an optically-stabilized semiconductor laser. A commercially available AlGaAs laser diode which emits a maximum power of 10 mW at =740 nm is operated in an extended-cavity configuration. Dispersion prisms are used in the extended cavity to obtain longitudinal-mode selection with low loss of optical power. The output is focussed into an optically isolated high-finesse ring resonator which contains a LiIO₃ crystal for second-harmonic generation. One potential application of this laser source is the optical excitation and laser cooling of ytterbium in an ion trap. In a related demonstration experiment, the frequency-doubled diode laser is applied to excite the =369.5 nm ² S _1/2-² P _1/2 transition of ytterbium ions in a hollow-cathode discharge.     

Low threshold, actively Q-switched Nd:YVO4 self-Raman laser and frequency doubled 588 nm yellow laser

We reported an actively Q-switched, intracavity Nd³⁺:YVO₄ self-Raman laser at 1176 nm with low threshold and high efficiency. From the extracavity frequency doubling by use of LBO nonlinear crystal, over 3.5 mW, 588 nm yellow laser is achieved. The maximum Raman laser output at is 182 mW with 1.8 W incident pump power. The threshold is only 370 mW at a pulse repetition frequency of 5 kHz. The optical conversion efficiency from incident to the Raman laser is 10%, and 1.9% from Raman laser to the yellow.     

Frequency doubling of wavelength locked laser diOde with a transmission-type filter in a confocal optical configuratiOn

Direct frequency doubling of a wavelength locked laser diode with an optical bandpass filter in a confocal optical configuration is demonstrated. The wavelength of the laser diode was locked in single longitudinal mode oscillation and tuned to phase-matching wavelength of a quasi-phase-matched second harmonic generation device based on a LiTaO₃ Waveguide. Stable blue light of 4.2 mW was obtained for incident power of 48 mW.     

175 to 210 nm widely tunable deep-ultraviolet light generation based on KBBF crystal

We have developed a widely tunable deep-ultraviolet (DUV) laser in the wavelength range from 175 to 210 nm by the fourth harmonic generation of Ti:Sapphire laser. The fourth harmonic generation is performed by direct second-harmonic generation (SHG) of a frequency doubled Ti:Sapphire laser with KBBF crystal. The highest output power is 2.23 mW at 193 nm, and the power of the DUV laser is more than 1 mW from 182 nm to 210 nm. To our knowledge, it is the first demonstration of milliwatt-level widely tunable DUV all-solid-state laser below 200 nm by direct SHG technique.     

Diode-pumped Nd:GAGG-LBO laser at 531 nm

We report a green laser at 531 nm generation by intracavity frequency doubling of a continuous wave (cw) laser operation of a 1062 nm Nd:GAGG laser under in-band diode pumping at 808 nm. A LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.5 W, as high as 933 mW of cw output power at 531 nm is achieved. The fluctuation of the green output power was better than 3.5% in the given 4 h.     

Diode pumped Pr<Superscript>3+</Superscript>:LiYF<Subscript>4</Subscript>-BBO ultraviolet laser at 320 nm

A diode pumped Pr³⁺:LiYF₄ laser at 639.5 nm has been demonstrated. With an incident pump power of 920 mW, the maximum red output power was 272 mW. Moreover, intracavity second-harmonic generation (SHG) has also been achieved with a maximum ultraviolet power of 23 mW by using a β-BaB₂O₄ (BBO) nonlinear crystal. To the best of our knowledge, this is the first report on continuous-wave ultraviolet generation by intracavity frequency doubling Pr³⁺:LiYF₄ laser.     

Degree of conversion and temperature increase of a composite resin light cured with an argon laser and blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature (T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (°C) of the microhybrid composite resin (Filtek? Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm² for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen (model MB 102, Quebec, Canada). Spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm^?1 resolution, 300 to 4000-cm^?1 wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1638 cm^?1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm^?1). For T (°C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (°C) were submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% (100 to 1000 mW/cm²) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm²) for an LED. The temperature change values varied from 1.1 to 13.1 °C (100 to 1000 mW/cm²) for an argon laser and from 1.9 to 15.0 °C (100 to 1000 mW/cm²) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both lightcuring units.     

Power spectrum and blood flow velocity images obtained by dual-beam backscatter laser Doppler velocimetry

We developed a micro multipoint laser Doppler velocimeter (μ-MLDV) for noninvasive in-vivo measurements of blood flow and we presented the results of demonstrations performed on experimental animals. In this paper, we investigate the validity of power spectrum analysis for determining the flow velocity and the minimum power of the semiconductor laser in the μ-MLDV. Although average velocity is generally estimated from a peak position (f _peak) in the power spectrum, the power spectrum of blood flow included an additional component in the high-frequency region. The conventional method for determining the average velocity of flows of transparent artificial fluids, which involves determining the average velocity from f _peak, is unsuitable for in-vivo measurements of blood flow. The laser power was reduced from 140 to 30mW since 30mW was the minimum power at which images of blood flow velocity in microvessels could be obtained. About 30mW (power density of 15mW/mm²) is the maximum power which can be irradiated to humans. Further reduction in the laser power is necessary before this technique can be applied to humans.     

高效频率转换下双波长外腔共振和频技术研究

基于外腔的高效频率转换, 尤其是当系统运行在抽运不消耗近似机理下, 信号光可实现大于90%的转换, 因此无法通过信号光直接获得其到腔模频率锁定的误差信号. 本文通过对信号光调制、和频光解调的方法获得了该误差信号, 实现了双波长激光到外腔腔模的级联锁定. 实验中外部环形腔将1.3 W的1064 nm抽运光放大到约14.3 W. 当1583 nm信号光从10 μW变化到50 mW, 其到636 nm和频光的转化效率约为73%; 当从50 mW变化到295 mW时, 转换效率呈线性降低到60%, 最终获得了440 mW的636 nm激光.     

High resolution ethylene absorption spectrum between 6035 and 6210 cm-1

A two-channel photo-acoustic spectrometer (PA spectrometer) with a near infrared diode laser was used for taking measurements of a high resolution ethylene absorption spectrum. A semiconductor TEC-100 laser with an outer resonator generates a continuous single-frequency radiation in the range 6030–6300 cm^-1. A newly designed model of photo-acoustic detector (PAD) in the form of a ring type resonator provides for measurement of weak absorption cross-section equal to 4×10^-23 cm²/mol at a laser radiation power of 3 mW. The PAD threshold sensitivity is 2×10^-9 cm^-1 Hz^-1/2 W, when the signal to noise ratio equals to 1. The ethylene absorption spectrum within the range 6035–6210 cm^-1 was measured for the first time with a spectral resolution of 10 MHz. The reported line centre positions have an uncertainty of ± 0.0005 cm^-1. The precise measurements of ethylene absorption cross-sections were carried out using the mixture of high purity ethylene and broadening gas (nitrogen) at the mixture ratio 1:50–1:200. Measurements were carried out at a mixture pressure of about 4.2 kPa. PACS 42.62.Fi; 42.55.Px