Four-plate birefringent filter for high-gain pulsed dye laser tuning

A complete quantitative analysis of a multistage birefringent filter has been used to design a four-plate filter for a high-gain dye laser. It is shown that both S and P polarization modes must be considered at all stages. The four-plate design, with thickness ratios of 1:2:4:8, succeeds where typical commercial designs (1:2:15 and 1:4:16) fail when used in a high-gain cavity. Calculations have been verified by performance measurements for a quartz filter. Design specifications are presented.     

Compact stacking of diode lasers for pulsed light sources of high brightness

A compact stacking architecture for high-power diode-laser arrays is proposed and compared with traditional stacks. The objective of compact stacking is to achieve high brightness values without the use of microlenses. The calculated brightness for a compact stack is over 300 W mm(-2) sr(-1), which is approximately 40 times higher than that of a traditional stack made of similar laser emitters. Even higher brightness values of over 600 W mm(-2) sr(-1) were reached in practice. A laser head was manufactured in which the light from several compact laser stacks could be fiber coupled or the light could be transformed to a highly uniform beam.     

Precisely tunable, narrow-band pulsed dye laser

Anarrow-band, precisely tunable dye laser pumped by an injection-seeded YAG laser is described. The laser achieves an output of 100 mJ/pulse and 40% efficiency when one uses Rhodamine 6G dyes. The output pulse is Gaussian both in time and spatial profile. The laser oscillator employs an intracavity étalon that is repetitively pressure scanned over one free spectral range while the grating successively steps to consecutive étalon modes. We pressure scanned the étalon under computer control using a bellows. Methods are described for calibrating the tuning elements for absolute precision. We demonstrated that the laser has an absolute precision of ±0.4 pm over a 1.0-nm scan. This accuracy is achievable over the wavelength range of a dye.     

Application of a galvanometric amplifier for measuring weak signals

Conclusions An amplifier containing in its input circuit an overdamped galvanometer possesses for equal fluctuation sensitivity thresholds a smaller reading stabilization time than a tuned amplifier stage either with electron tubes or transistors. This is particularly noticeable in recording extremely small dc emfs and in measuring 10 Hz signals.     

Design and testing of a large-aperture, high-gain, Brewster 's angle zigzag Nd:glass slab amplifier

At the University of Rochester we have constructed and tested a large-aperture, (1.0 x 6.5 cm), high-gain (8) Brewster 's angle zigzag Nd:glass amplifier with a repetition rate of 2 Hz. This amplifier has a gain uniformity of +/-3 % and a maximum stress-induced depolarization <2.5 %.     

Compact all-fiber pulsed coherent Doppler lidar system for wind sensing

A compact 1.5 microm all-fiber pulsed coherent Doppler lidar system for wind sensing, which includes the functions of variable pulse width and automatic polarization control has been developed. The system configuration is introduced and key components used in the system are explained. Theoretical performances of the system in wind sensing are estimated and compared with experimental results. The measurable range corresponding to the detection probability of >80% is approximately 1 km or more in the case of 150 m range resolution under the normal atmospheric conditions.     

微小电压测量放大电路的抗共模噪声设计方法

测量仪器性能的好坏在很大程度上取决于其前端放大电路的性能,常选择具有较强噪声抑制能力和较大输入阻抗的运算放大电路和仪用放大电路.在微小电压的精密测量时,仪用放大电路的对称性很难完全保证,在强噪声的环境中,在仪用放大电路中加入共模电压的负反馈电路可抵消共模噪声或其中的一部分;在长距离信号传输时,在电路输入端加入跟随器电路可很好地克服由于测量电缆较长造成的输入电路不平衡而引入的测量误差.实验测试结果表明:改进型的仪用放大电路噪声抑制效果良好.     

The optimal measurement time for short-lived weak radioactive sources

It is shown that an optimal measurement time can be simply determined for short-lived weak sources. The calculated values are presented in a widely applicable graphic form.     

Beryllium neutron activation detector for pulsed DD fusion sources

A compact fast neutron detector based on beryllium activation has been developed to perform accurate neutron fluence measurements on pulsed DD fusion sources. It is especially well suited to moderate repetition-rate (<0.2 Hz) devices, such as the plasma focus or Z-pinch. The detector comprises a beryllium metal sheet sandwiched between two large-area xenon-filled proportional counters. A methodology for calculating the absolute response function of the detector using a “first principles” approach is described. This calibration methodology is based on the ⁹Be(n,α)⁶He cross-section, energy calibration of the proportional counters, and numerical simulations of neutron interactions and beta-particle paths using MCNP5. The response function R(E_n) is determined over the neutron energy range 2-4 MeV. The count rate capability of the detector has been studied and the corrections required for high neutron fluence measurements are discussed. For pulsed DD neutron fluencies >3×10⁴ cm⁻², the statistical uncertainty in the fluence measurement is better than 1%. A small plasma focus device has been employed as a pulsed neutron source to test two of these new detectors, and their responses are found to be practically identical. Also the level of interfering activation is found to be sufficiently low as to be negligible.     

Ultranarrow-linewidth, efficient amplification of low-power seed sources by a fiber amplifier

We report efficient amplification of an external cavity diode laser in the 1.06-mum range. The diode laser radiation is coupled into a Nd-doped silica fiber. The fiber is pumped by a diode array with up to 6.15 W of power. After a single pass of the seed radiation through the fiber amplifier, we observe up to 1.74 W of single-mode, narrow-linewidth laser radiation that is tunable over a relatively wide range of 1.060-1.067 mum. The output from our amplifier has the same spectral characteristics as the seed beam.     

Experimental and theoretical investigation of a multipass, plane mirror, femtosecond dye laser amplifier

Femtosecond pulses of a passive mode-locked Rhodamine-6G dye laser are amplified in a double-stage, three-pass, plane mirror, Sulforhodamine-101 amplifier system. Saturable filters (Schott glass RG645 and Malachite Green) are used to suppress amplified spontaneous emission. Input pulses of 110-fs duration are broadened to 240 fs in the amplifier system and recompressed to 75 fs in a prism-pair compressor. Using a 20-Hz Q-switched Nd:YAG pump laser of 50-mJ second-harmonic output energy, we obtained amplified and recompressed pulses of 180-μJ energy at 625 nm starting with 40-pJ input pulses. The small-signal amplification dynamics is studied numerically. Relevant gain dye and saturable filter parameters are derived. The influence of amplified spontaneous emission is analyzed.     

A macromodel of an operational amplifier for modelling measurement circuits with pulsed signals

A modified macromodel of an operational amplifier for the PSpice program and a method of calculating its parameters are considered. The macromodel enables one to reproduce authentically specified values of the asymmetrical maximum rate of growth of the output voltate of an operational amplifier. Translated from Izmeritel'naya Tekhnika, No. 9, pp. 26–29, September, 1999.     

Test of adiabatic spin flippers for application at pulsed neutron sources

Experimental results on the flipping efficiency are shown for a set of 2 V-coils as spin flipper and for a high-frequency flipper with adiabatic transition. The influence of the adiabaticity parameter is discussed. The merits of these adiabatic flippers are compared with the use of “monochromatic” flippers, when operated in a beam from a pulsed neutron source. It is concluded that for “long pulse” sources adiabatic flippers will be superior.     

Features of the pulsed inductive discharge formation for pumping gas-discharge radiation sources

The process of pulsed transverse inductive discharge formation has been experimentally studied depending on the parameters of an active gaseous medium and a discharge excitation circuit. It is established that optimum conditions for obtaining inductively coupled plasma in a transverse vortex field that excites the gaseous medium are achieved by excitation inductors with inductances of 50–300 nH, to which up to 30% of the energy of a pumping LC oscillator can be transferred. It is concluded that the energy stored in these excitation inductors can be effectively used in spontaneous and coherent radiation sources.     

First experimental implementation of pulse shaping for neutron diffraction on pulsed sources

One of the central issues in the design and the use of pulsed neutron sources is the control of pulse length in elastic scattering experiments, most significantly diffraction on crystalline matter. On the existing short pulse spallation sources the strongly wavelength dependent source pulse length that determines the resolution is permanently fixed on each beam line by the type of the moderator it faces. We have experimentally implemented for the first time the wavelength frame multiplication (WFM) multiplexing chopper method, an earlier proposed variant of the by now fully tested repetition rate multiplication technique for inelastic scattering spectroscopy on pulsed neutron sources. We have operated the time-of-flight diffractometer at the continuous reactor source at BNC in an unconventional multiplexing mode that emulates a pulsed source. As a full proof of principle of the WFM method we have experimentally demonstrated the extraction from each source pulse a series of polychromatic, chopper shaped neutron pulses, which can continuously cover any wavelength band. The achieved 25 μs FWHM pulse length is shorter than that can be obtained at all at short pulse spallation sources for cold neutrons. The method allows us to build efficient, high and variable resolution diffractometers at long pulse spallation sources.