Tunable extended-cavity diode laser stabilized on iodine at lambda = 633 nm

We present a tunable extended-cavity semiconductor laser, based on the Littman configuration, which has been frequency-stabilized to Doppler-free hyperfine transitions in I(2). The stability was measured compared with the reference He-Ne-I(2) laser system, whereas the semiconductor laser was locked on components of the P(33) 6-3 transition close enough to the reference R(127) 11-5 line to allow beat frequency counting. A relative stability of 4 x 10(-12) over a 100-s integration time was achieved. The laser configuration allowed mode-hop-free tuning over a range including the P(33) 6-3 transition and the group of strong overlapping transitions R(60) 8-4, R(125) 9-4, and P(54) 8-4 with higher signal-to-noise ratio than the P(33) 6-3 located approximately 13 GHz toward lower optical frequencies.     

Stabilization of an 852 nm extended cavity diode laser using the Zeeman effect

Abstract

We demonstrate the use of the Zeeman effect in Cs vapour to stabilize an ultra-compact extended cavity diode laser (ECDL) operating at 852 nm. We investigate the expected laser stabilization error signal for a range of magnetic fields and are able to tune the locked ECDL by variation of the magnetic field. We also study in detail the tuning of the laser frequency using optical methods. The ECDL has a linewidth of 520kHz and the drift, when locked, is of the order of 5 MHzh^?1.     

633nm碘稳定激光器作为长度基(标)准的比对测量

简述作为长度基（标）准用的633nm碘稳定激光器的技术指标以及它的测量方法，文中以作者所进行的国际和国内比对中的测量结果为例，给出了这类激光器可以复现的频率或波长不确定度。     

Frequency stabilization of an external cavity diode laser to molecular iodine at 657.483 nm

The saturation spectrum of the P(84) 5-5 transition of 127I2 at 657.483 nm is obtained with the third-harmonic demodulation method using an external cavity diode laser. The laser frequency is modulated by modulating the diode current instead of modulating the cavity length with a piezoelectric transducer (PZT). Current modulation allows a modulation frequency that is higher than PZT modulation. The signal-to-noise ratio of 1000 is better than previous results presented in the literature. The laser is frequency stabilized to the hyperfine component o of the P(84) 5-5 transition with a frequency stability of better than 10 kHz (2.2 x 10(-11) relative stability).     

International comparison of 127I2-stabilizedHe-Ne Lasers at λ≈633 nm using the third and the fifthharmonic locking technique

In an international comparison of ¹²⁷I₂-stabilized helium-neon lasers at λ≈633 nm, lasers from the CMI and the BIPM were stabilized by the third (THT) and the fifth (FHT) harmonic locking techniques. A frequency shift to the blue was measured when using the FHT technique. The influence of weak components of the rotational-vibrational transition P(33) 6-3 of the molecule ¹²⁷I¹²⁹I on the frequency shift of components d, e, f, and g of the line R(127) 11-5 is evaluated     

High-temperature buried InP/GaInAsP heterostructure laser diode emitting at 1310 nm

As a continuation of our studies aimed at creating semiconductor lasers based on buried InP/GaInAsP heterostructures, we consider the design and fabrication aspects of 1310-nm laser diodes for operation at elevated temperatures. We report the key features of the fabrication process and parameters of the laser emitters at temperatures of up to 120°C, and present their power-current and spectral characteristics.     

The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.     

Short-range synthetic aperture imaging at 633 nm by digital holography

We present an active optical synthetic aperture-imaging system. A phase-step digital holographic setup is used as a wavefront sensor in the far field. The overlap of the holograms enables the estimation and compensation of their relative positions and phase with a speckle cross-correlation algorithm. Experimental results on a short-range synthetic aperture setup at 633 nm are presented that are based on 128 x 128 holograms. The synthesis is executed in one direction by means of rotation of the object. Test images show a significant gain of resolution in the synthesis direction. Processing errors are estimated through experiment. Random processing errors of a synthetic pupil composed of 33 merged holograms are negligible, but biases induced by unknown optical aberrations ofthe reference wave induce defocusing and astigmatism.     

Tunable external-cavity diode laser at 650 nm based on a transmission diffraction grating

A tunable external-cavity diode laser (ECDL) based on a transmission diffraction grating in a Littrow mount has been developed and characterized. A single-transverse-mode diode laser at 650 nm is used in an external-cavity configuration in which the transmission grating is used as a dispersive element to select the single longitudinal mode. The transmission diffraction grating is made with electron-beam lithography. A tunable true single-mode cw output power of >20 mW is obtained from the ECDL. The total wavelength tuning range is 12 nm, and the mode-hop-free continuous tunability is >20 GHz.     

一种新型的碘稳定633 nm He-Ne激光系统

介绍了基于非饱和蒸汽压的碘稳定633 nm He-Ne激光系统,其碘室无需控温装置.激光器的腔长为26 cm,输出功率为0.3 mW,激光调谐范围能够覆盖从a到n的14个吸收峰.通过拍频测量实验,其频率的相对标准不确定度达到6.3×10-11.1 000 s的频率稳定度优于2.5×10-12.该稳频激光系统已被用于国产的量块干涉仪和绝对重力仪中.     

Three-longitudinal-mode He-Ne laser frequency stabilized at 633 nm by thermal phase locking of the secondary beat frequency

We present a simple scheme for thermal frequency stabilization of a three-longitudinal-mode He-Ne laser at 633 nm with improved short-term (5 x 10(-11) at 1-s average time) and long-term (124-kHz standard deviation for 10 h) frequency stability. A stabilized output power of 3 mW was readily obtained from the central mode by polarization-mode selection. The optical frequency of the central mode could be precisely tuned by an external frequency reference over 160 MHz with high precision or could be optically phase locked to a reference laser by use of a thermal frequency-stabilization circuit and an external acousto-optic modulator. The laser will be useful in various applications for which a laser source with high power and frequency stability is necessary.     

941nm连续波高功率半导体激光器线阵列

用金属有机化合物气相淀积(MOCVD)技术生长了InGaAs／GaAs／AlGaAs分别限制应变单量子阱激光器材料。利用该材料制成了半导体激光器线阵列,连续波工作条件下的中心激射波长为940．5nm,输出功率高达37．7W(45A、2．0V),斜率效率可达0．99W／A(外微分量子效率为75％),最高转换效率超过45％,阈值电流密度为117A／cm^2,该波长的半导体激光器是Yb：YAG固体激光器的理想泵浦源。     

An Accurate Value for the Absorption Coefficient of Silicon at 633 nm

High-accuracy transmission measurements at an optical wavelength of 633 nm and mechanical measurements of the thickness of a 13-µm thick silicon-crystal film have been used to calculate the absorption and extinction coefficients of silicon at 633 nm. The results are 3105±62 cm⁻¹ and 0.01564±0.00031, respectively. These results are about 15% less than current handbook data for the same quantities, but are in good agreement with a recent fit to one set of data described in the literature.     

Sub-millisecond photorefractive two-wave coupling in Bi12TiO20 at 633 nm

Abstract

The unusually fast response of the two-wave mixing process in fibre-like Bi₁₂TiO₂₀ crystals on transient change of the external electric field was experimentally observed. Pulses of the amplification of the signal wave with a rise time of 0.2 ms and a width of 0.5 ms at a total input intensity of 6 mW mm^?2 are obtained when applying a rising or decreasing front of an external electric field to the crystal. The two-wave coupling without external field has a response time of 200 ms. A simple calculation based on the bandtransport model qualitatively explains the fast transient amplification but fails to explain the slow response without the electric field.     

Tunable diffraction-limited light at 488 nm by single-pass frequency doubling of a broad area diode laser

A laser system that is based on second-harmonic generation of a broad area laser diode and provides 23.2 mW of diffraction-limited light with narrow bandwidth is described. It is tunable from 487.4 to 489 nm. The broad area laser diode is frequency stabilized in an external cavity that yields 800 mW of diffraction-limited light. This infrared light is converted into the visible by use of a 1 cm periodically poled MgO:LiNbO(3) bulk crystal with a measured single-pass conversion efficiency of up to 3.6%/W x cm.     

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.     

Absolute interferometry with a 670-nm external cavity diode laser

In the past few years there has been much interest in use of tunable diode lasers for absolute interferometry. Here we report on use of an external cavity diode laser operating in the visible (lambda ~ 670 nm) for absolute distance measurements. Under laboratory conditions we achieve better than 1-mum standard uncertainty in distance measurements over a range of 5 m, but significantly larger uncertainties will probably be more typical of shop-floor measurements where conditions are far from ideal. We analyze the primary sources of uncertainty limiting the performance of wavelength-sweeping methods for absolute interferometry, and we discuss how errors can be minimized. Many errors are greatly magnified when the wavelength sweeping technique is used; sources of error that are normally relevant only at the nanometer level when standard interferometric techniques are used may be significant here for measurements at the micrometer level.     

Nonlinear optical and optical limiting properties of phthalocyanines in solution and thin films of PMMA at 633 nm studied using a cw laser

We present our results on nonlinear optical (NLO) and optical limiting properties of Tetra tert-butyl phthalocyanine and Zinc tetra tert-butyl phthalocyanine studied at 633 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. We have observed low power optical limiting, with low limiting thresholds, based on nonlinear refraction in both the samples. We also present results on the NLO properties of the same dyes doped in Polymethylmethacrylate (PMMA). These studies indicate that both the phthalocyanines are potential candidates for low power optical limiting applications.     

Direct frequency counting with enhanced beat signal-to-noise ratio for absolute frequency measurement of a He-Ne/I2 laser at 633 nm

We obtain a heterodyne beat signal between an iodine-stabilized He-Ne laser at 633 nm and a low power comb mode of an optical frequency synthesizer with an enhanced signal-to-noise ratio (SNR) up to approximately 35 dB. This is accomplished by the adoption of a fiber coupler and the reduction of the shot noise induced by adjacent comb modes. SNR is improved more than 15 dB compared with that of conventional methods. We measure the absolute frequency of the He-Ne laser mentioned above directly utilizing the enhanced SNR. A quantitative analysis of SNR and some information on experimental criteria for the correct frequency counting are given.