Fixed-wavelength operation of a copper-laser-pumped dye laser injection seeded by low-power He-Ne lasers

The design and operating characteristics of a dye laser pumped by a 3-W copper-vapor laser (CVL) and injection seeded by low-power (1-5 mW) He-Ne lasers at 633 nm are reported. An extremely simple optical arrangement is used wherein the output mirror of the He-Ne laser and a third mirror form the dye laser cavity. Laser efficiency in fixed-wavelength operation has been investigated for variable CVL pump power, He-Ne injection power and polarization, and cavity output coupling for a standard Rhodamine 590/Rhodamine 640 dye solution. Over 90% of free-running (unseeded) laser power is obtained in fixed-wavelength (seeded) operation at low CVL pump powers (≤1 W), dropping to approximately 60% at 3-W pump power. Maximum CVL pump to dye laser optical conversion efficiency in narrow-band, fixed-wavelength operation at 633 nm was 12%.     

Design and test of a simple high-temperature laser microrefractometer

The design of a laser microrefractometer that is suitable for temperature-dependent measurements is described. The refractive index of methylene iodide is measured in the temperature range of 22-92 °C for laser wavelengths covering almost the entire visible range of the spectrum: 442, 488, 515, 543, 594, and 633 nm. A detailed analysis of the temperature-related experimental error is made.     

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.     

Infrared and laser spectroscopic characterization of aluminium defects in cultured quartz

Optical absorption at He-Ne and argon laser frequencies has been used to map the distribution of aluminium-hole centres, Al-H(+), in irradiated and vacuum swept quartz. The absorption band associated with Al-h(+) has a strong peak centered at 435 nm and a weaker one at 633 nm. Argon laser lines at 488 and 514.5 nm are close to the wavelength of the stronger peak, while the He-Ne line at 632.8 nm is nearly coincident with that of the weaker peak. Large variations in Al-h(+) absorption for irradiated and vacuum swept crystals correspond to visually observed changes in coloration. The laser method is sensitive and nondestructive, and gives a quantitative measurement adaptable to computerized scanning and recording of data. Measurements of both Al-h(+) and infrared-active aluminium hydroxide centres, Al-OH(-), are used to evaluate the distribution of aluminium-associated defect centres and determine aluminium variations over an entire crystal.     

An International Comparison of Absolute Radiant Power Measurement Capabilities

We report the results of an intercomparison of monochromatic radiant power measurement capabilities recently completed by 11 national laboratories. The intercomparison radiometers, distributed in pairs, included an amplifier with six decades of precision gain and one of two types of silicon photodiode (pn or np-type construction). Eleven of the laboratories measured the absolute responsivity of the radiometers at 633 nm and nine at 488 nm. The standard deviation of the overall difference was 0.36% at both wavelengths. The agreement between the various participating laboratories and NIST was within the measurement accuracy stated by the participants.     

A Radiometer for Precision Coherent Radiation Measurements

A radiometer has been designed for precision colierent radiation measurements and tested for long-term repeatability at wavelengths of 488 and 633 nm. The radiometer consists of a pn silicon photodiode maintained in a nitrogen atmosphere with a quartz window designed to eliminate interference problems. Ratio measurements between the radiometer and an absolute type detector were made over a period of 215 d. At 0.5 mW, the standard deviations were 0.008% and 0.009% at 488 and 633 nm, respectively. The maximum deviations from the mean were 0.016% and 0.015% at the respective wavelengths. Measurements were also made on the radiometer with respect to angular and spatial uniformity and linearity. The high precision, simplicity, and portability of the radiometer suggest it for use as a transfer standard for radiometric measurements.     

Instrumentation for multistep excitation of lithium atoms to Rydberg states

We have developed a diode laser apparatus to excite Li from its ground 2S state, through 2P and 3S, to its Rydberg states with three cw diode lasers operating at λ = 671 nm, 813 nm, and 630-635 nm. A He-Ne laser at λ = 633 is sometimes used in place of the 635-nm diode laser for the last step. The output power of each of these lasers was ~1 mW. We describe our technique of locking the first two lasers on Li resonance lines by obtaining a fluorescent signal from the second decay (3S ? 2P) that is normally overpowered by a strong background of fluorescent light from the first decay (2P ? 2S). We used two balanced photodiodes to reject the strong fluorescent light without loss of collection efficiency. A rejection ratio as high as 100 has been obtained.     

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.     

Results of International Comparisons Using Methane-Stabilized He-Ne Lasers at 3.39 ?m and Iodine-Stabilized He-Ne Lasers at 633 nm

The results of international comparisons of methane-stabilized He-Ne lasers at ? = 3.39 ?m and iodine-stabilized He-Ne lasers at 633 nm, made by beat frequency techniques, between Bureau International des Poids et Mesures (BIPM) and eleven national laboratories are presented. Generally, the measured frequency differences were inside ±4 × 10-11; but greater frequency differences were observed with some iodine cells (probably as a result of contamination) or when the output power of one laser was two or three times greater than the power of the other laser.     

635/808双波长低强度照射对术后创口愈合的影响(英文)

本文通过评估635/808双波长低强度激光照射对术后病人创口愈合的影响,以给临床应用提供病例参考。随机选取外科手术治疗的非恶性肿瘤患者60例,试验组和对照组各30例。试验组使用635nm/808nm双波长激光辅助切口治疗,对照组以波长635nm的He-Ne激光辅助治疗。激光器发出两路激光对受试者切口部位进行照射治疗,一路波长为(635±5)nm,光功率密度1～6.5mW/cm2,另外一路波长为(808±5)nm,光功率密度为11～32mW/cm2。激光照射治疗开始于手术结束24h之后,每天一次,每次照射15min,至治疗终点(出院或切口愈合拆线),双波长激光器最大功率密度控制在40mW/cm2以下(可调节),最大能量密度在36J/cm2以下(可调节)。He-Ne激光器输出功率最大为100mW,每天一次,每次照射15min,至治疗终点(出院或切口愈合拆线)。试验表明,635/808双波长低照度照射能够促进创口愈合,治疗效果好于He-Ne激光器。     

Two-longitudinal-mode He-Ne laser for heterodyne interferometers to measure displacement

We propose a new configuration for a high-resolution heterodyne interferometer that employs a two-longitudinal-mode He-Ne laser with an intermode beat frequency of 600-1000 MHz. The high beat frequency is downconverted to 5 MHz such that the phase change of the interferometer output is precisely measured with a displacement resolution of 0.1 nm. A thermal control scheme is adopted to stabilize the cavity length of the He-Ne plasma tube such that a frequency stability of 2 parts in 10(9) is obtained by suppression of frequency drifts caused by t he phenomena of frequency pulling and polarization anisotropy. This two-longitudinal-mode He-Ne laser yields a high output power of 2.0 mW, which permits multiple measurements of as many as 10 machine axes simultaneously.     

Frequency shifts of iodine stabilized He-Ne lasers at higherharmonic order stabilization

The frequency shifts of an ¹²⁷I₂ stabilized He-Ne laser at 633 nm have been measured at the third, fifth, and seventh harmonic stabilization using a digital signal processing lock-in amplifier. The observed frequency shifts confirmed the previous theoretical prediction that the laser frequency depends on the harmonic order of stabilization. The lower effects of modulation amplitude shift, power shift, and iodine pressure shift at the fifth harmonic stabilization indicate a potential improvement of the frequency reproducibility of the laser standard. A model is suggested to describe the power shifts of the laser. The mechanism explains the lower power shift of some lasers when they are operated at relatively high intracavity power     

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.     

Long-term frequency-stabilized Ar-ion laser system for high-resolution Raman spectroscopy of gases

An Ar-ion laser with a measured single-mode linewidth of 5 MHz at 488 nm has been stabilized to approximately 1 MHz. The stabilization has been obtained by means of a Fabry-Perot interferometer as wavelength reference and a solid étalon as mode selector. The error signal is generated by modulation of the length of the laser cavity. The stabilization system is able to keep the wavelength fixed for periods of more than 100 h.     

Iodine-stabilized extended cavity diode laser at λ=633 nm

An extended cavity diode laser at 633 nm has been frequency stabilized to I₂-Doppler-free absorption signals of the P(33)6-3 transition using a third-harmonic detection technique. The frequency was measured by the beat-frequency technique with an iodine-stabilized He-Ne laser as reference. A minimum value for the two-probe relative standard uncertainty of 1× 10^-11 (5 kHz) is reached after 100 s. We also report measurements of the hyperfine splittings of the P(33)6-3 transition and laser frequency dependence on modulation amplitude and iodine pressure     

天津牌医用氦氖激光CT胶片

天津牌医用氦氖激光CT胶片，又称数字技术医用胶片，对633nm-670nm波长光谱有很高的灵敏度，主要适用于医疗诊断中的氦氖激光扫描仪，以记录CT、MRI、DSA等图像信息，也可用于固态红色激光二极管为光源的激光扫描仪。该胶片的乳剂颗粒细而均匀，影像分辨率高，清晰度好，信息容量大，而且性能稳定，保存性好，显影宽容度大，质量已全面达到一些国际名牌的同类产品水平。     

Comparison between the 127I2 Stabilized He-Ne Lasers at 633 nm and 612 nm of the BIPM and the IMGC

In November 1981, a comparison between BIPM and IMGC He-Ne lasers stabilized to saturated absorption lines of 127I2, at the wavelengths ? = 633 nm and ? = 612 nm has been made at the BIPM. At 633 nm, a repeatability and a reproducibility within +1 × 10-11 · ? have been obtained. At 612 nm, a repeatability within a few 10-11 · ? only for one laser and a reproducibility of ± 2 × 10-10 · ? have been obtained.     

Iodine stabilized dye laser system for frequency measurements in the visible and near IR region of the spectrum

An iodine stabilized dye laser system is described that provides traceable measurement of reference frequencies in the visible spectrum from 540 to 670 nm and in the near infrared at 1.15 /spl mu/m. The system allows calibration of the widely used 633 nm, 612 nm, and 543 nm HeNe laser systems. Also, frequency measurements of a polarization stabilized 1153 nm HeNe laser have been performed via frequency doubling and comparison with the dye system operating on the corresponding 576 nm lines. Studies of the shift sensitivities of the system at various wavelengths of interest are described for variation of iodine cell pressure, laser modulation amplitude, and optical saturation power. The dye system was also stabilized to hyperfine components associated with the 6-3 P(33) iodine transition and compared with a 633 nm iodine stabilized HeNe standard.     

Calculating parameters of high-power He-Ne Lasers operating at λ = 0.63 μm

The existing methods of calculation of the parameters of He-Ne lasers agree with experiment for laser powers not exceeding 30–50 mW. We propose a method applicable to lasers operating at λ = 0.63 μm with a maximum output power exceeding 100 mW.     

Thermal and optical properties of polymer hosts for solid-state dye lasers.

We present measurements of thermal and optical properties of poly(methyl methacrylate) (PMMA), PMMA modified by the addition of ethanol (MPMMA), and copolymers of methyl methacrylate with 2-hydroxyethyl methacrylate [P(HEMA:MMA)]. Spectral transmission of the polymers is excellent (alpha = 0.5 cm(-1) at 400 nm, decreasing to 0.04 cm(-1) at 633 nm). Measured laser damage thresholds of MPMMA and P(HEMA:MMA) show at least a twofold increase over PMMA. Thermal lensing measured in these hosts doped with Rhodamine 6G is shown to be similar (f = -450 mm for pump power of 200 mW in a 2-mm-diameter spot, scaling with pump intensity). Compared with MPMMA, P(HEMA:MMA) offers an improved surface quality and a more uniform dye distribution.