Brewster Windows Research Articles

Generating vector beams by modulating and superimposing multiple polarization modes within a helium-neon resonant cavity

In recent years, vector beams, which have greater control freedom due to their non-uniform spatial polarization distribution, have received extensive attention from scholars. In this paper, we present a straightforward intracavity modulation method by increasing the volume of the gas gain medium inside the cavity to induce multimode oscillation. Subsequently, Brewster windows and a curved-output mirror are used to achieve polarization control and superposition of multiple modes within the cavity to generate stable and controllable vector beams. In addition, the polarization purity of the radial vector beam and the angular vector beam can reach 87.98% and 85.52%, respectively. This work can not only break the understanding of the traditional vector beam generation method and deepen the understanding of laser cavity regulation technology but also play a guiding role in designing compact vector lasers.

Portable diagnostic package for Thomson scattering and optical emission spectroscopy on Princeton field-reversed configuration 2 (PFRC 2).

An Advanced Research Projects Agency-Energy funded diagnostic system has been deployed to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The Portable Diagnostic Package (PDP), designed at Oak Ridge National Laboratory, allows for the measurement of Thomson Scattering (TS) for electron density and temperature and Optical Emission Spectroscopy (OES) for ion temperature, impurity density, and ion velocity. A tunable spectrometer on the PDP with three gratings provides the flexibility to measure low (1eV) and high (1000eV) electron temperature ranges from TS. Additionally, using a second spectrometer, the OES diagnostic can survey light emission from various ion excitation levels for wide wavelength ranges. The electron density (<2 × 1019m-3) of plasmas generated in PFRC-2 has been below the PDP TS discrimination threshold, which has made TS signal detection challenging against a high-background of laser stray light. The laser stray light was iteratively reduced by making modifications to the entrance and exit geometry on PFRC-2. Rayleigh scattering experiments on PFRC have yielded the TS discrimination sensitivity to be >1 × 1020m-3 for the PDP. A recently implemented narrow-band notch spectral filter that masks the second harmonic 532nm Nd:YAG laser wavelength has increased the system's TS light discrimination sensitivity 65 times compared to the instance when the notch filter was not implemented. The hardware implementation including design changes to the flight tubes and Brewster windows will be discussed, along with results from Rayleigh and rotational Raman scattering sensitivity analyses, which were used to establish a quantitative figure of merit on the system performance. The Raman scattering calibration with the notch filter has improved the PDP electron density threshold to 1 ± 0.5 × 1018m-3.

A simple method for astigmatic compensation of folded resonator without Brewster window

A folded resonator requires an oblique angle of incidence on the folded curved mirror, which introduces astigmatic distortions that limit the performance of the lasers. We present a simple method to compensate the astigmatism of folded resonator without Brewster windows for the first time to the best of our knowledge. Based on the theory of the propagation and transformation of Gaussian beams, the method is both effective and reliable. Theoretical results show that the folded resonator can be compensated astigmatism completely when the following two conditions are fulfilled. Firstly, when the Gaussian beam with a determined size beam waist is obliquely incident on an off-axis concave mirror, two new Gaussian beam respectively in the tangential and sagittal planes are formed. Another off-axis concave mirror is located at another intersection point of the two new Gaussian beams. Secondly, adjusting the incident angle of the second concave mirror or its focal length can make the above two Gaussian beam coincide in the image plane of the second concave mirror, which compensates the astigmatic aberration completely. A side-pumped continues-wave (CW) passively mode locked Nd:YAG laser was taken as an example of the astigmatically compensated folded resonators. The experimental results show good agreement with the theoretical predictions. This method can be used effectively to design astigmatically compensated cavities resonator of high-performance lasers.

Detectivity enhancement in THz electrooptical sampling

We demonstrate and discuss a simple scheme that significantly enhances the detectivity of THz electro-optical sampling by introducing a sequence of Brewster windows that increases the ellipticity of the probe beam. By varying the window material or the number of Brewster windows, the enhancement factor can be adjusted; we demonstrate an enhancement factor of ≈20 with four ZnSe Brewster windows. The scheme is particularly useful when very small THz fields are to be measured in connection with low-repetition rate amplified Ti:S laser systems.

Study of the dependence of the photoacoustic signal amplitude from methane on different collisional partners

In a previous work we observed that the photoacoustic signal from methane in air decreases to one-seventh the figure obtained in mixtures with pure nitrogen. A close resonance between oxygen's first vibrational mode (ν) and the methane bending modes may be responsible for this phenomenon. Indeed, the long relaxation time of the ν mode (1554cm−1) causes the oxygen to store energy internally instead of releasing it to heat. In this work we study different collisional partners (Helium, C2Cl2F4) which may help transfer this vibrational energy to kinetic.In order to carry out the experiment we used the resonant photoacoustic technique by means of an OPO tuned at 3.3μm, which corresponds to the methane ν3 vibrational mode, and an aluminum acoustic resonator with rectangular cross section, Brewster windows at the resonance nodes of the second longitudinal mode at 2300Hz and Q-factor of 165. A rate-equation-based model, which describes the time evolution of the excited populations and the heating of the sample for the case of Helium, shows good agreement with the experimental results. The addition of C2Cl2F4 showed an increase of the methane PA signal up to values even higher than for methane-nitrogen mixtures.

Polarization sensitive near-complete reflection from photonic crystal slab in centered rectangular lattice

In this study, reflective properties have been systematically calculated for two-dimensional photonic crystal slabs in centered rectangular lattices with elliptical patterns for transverse electric polarization along perpendicular x- and y-directions. The slab structures can be geometrically optimized for a near-complete reflection over a broad wavelength range. The reflection from the photonic crystal slabs is polarization selective, allowing a complete reflection for one polarization and complete transmission for the other polarization, which could be useful for a laser cavity mirror without using Brewster windows. The dependence of the reflection on the slab thickness and the structural parameters demonstrates the effect of guided-mode resonances on the reflection.

A Michelson Interferometer for Relative Phase Locking of Optical Beams

A Michelson-type interferometer is built to dynamically lock the optical phase difference between the two-arm laser beams. The phase difference is tunable and allowed for continuous adjustments nearly by 160°. Under the best locking condition, a relative phase stability better than 0.1° is achieved starting from the original phase jitter of 10 to 15°. The interferometer is made by simply adding a pair of Brewster windows in one arm of the conventional setup, yet it provides much robust phase locking. It is readily applicable for optical lattice construction and nondestructive phase contrast imaging of ultracold atoms.

Toward an accurate frequency standard at 1.5 μm based on the acetylene overtone band transition

We have made a frequency standard operating at the 1.5 /spl mu/m region using the saturated absorption of the v/sub 1/+v/sub 3/ band of /sup 13/C/sub 2/H/sub 2/. To enhance the moderate power from a laser diode and to saturate a very weak molecular overtone transition, we used a Fabry-Perot (FP) cavity and inside of it we put an acetylene cell. In order to obtain a longer life time for the cell, we designed a new scheme consisting of a cavity with a ULE (ultralow expansion) glass spacer and a baked and sealed-off cell with Brewster windows. We observed the saturated spectrum having a 1 MHz spectral linewidth. The signal obtained using the same cell ten months later had the same signal-to-noise ratio (SNR) and spectral linewidth. We made two versions of the frequency standard and observed a beat note between these two lasers from which we derived the frequency stability, in terms of the square root of the Allan variance /spl sigma/(/spl tau/)=2.4/spl times/10/sup -13/ at an integration time /spl tau/=1000 s.

UV lasing on Cu/sup +/ in a Ne-CuBr pulsed longitudinal discharge

UV lasing on copper ion transitions in CuBr vapor laser has been obtained in a nanosecond pulsed longitudinal discharge with Brewster windows and external mirrors. A record small-signal gain per unit length has been achieved (up to 19%/m and 16%/m for the 238.6- and 270.3-nm transitions, respectively). Infrared (IR) laser action on Cu ions in a He-CuBr discharge and on Ag ions in a He-AgI (silver iodide) discharge has also been observed. A maximum average output power of 430 mW has been achieved multiline (740.4-780.8 nm) on the Cu+ IR transitions. A maximal gain of 58%/m has been obtained on the strongest 780.8-nm transition.

Generation of 275.4-nm UV output from a large-frame argon-ion laser for fluorescence detection in capillary electrophoresis

A standard, relatively old, large-frame argon-ion laser, which is available in many laboratories, was modified to produce output in the deep-UV (275–306 nm) region by installing a set of inexpensive, commercially available laser mirrors. The deep-UV output is generally applicable as excitation wavelength in the field of biochemical and environmental analysis. However, it has received little attention in the literature, probably because a complete laser set-up normally requires a high investment. The modification described, which includes a thorough cleaning of the Brewster windows of the laser tube and a careful alignment of the laser, is a good alternative to this investment. In daily operation, only some minor realignments are required. As an illustration of the applicability, excitation with the 275.4-nm line was used for laser-induced detection of native fluorescent aromatic sulphonates in capillary electrophoresis.

High-gain ultraviolet Cu-II laser in a segmented hollow cathode discharge

We report measurements of the discharge and laser characteristics of an ultraviolet (UV) copper ion laser radiating on the 248.6- and 270.3-nm transitions. Our 50-cm active length laser operates in a high-voltage segmented hollow cathode discharge with Brewster windows and external mirrors. The lowest threshold currents were 7.3 and 5.6 A for the above transitions, respectively. The threshold current was found to increase with decreasing active length. We obtained superior gain characteristics (to 11.2 and 8.8%/m gain for the 248.6-and 270.3-nm transitions, respectively, at 0.3 A/cm linear current density) compared with previous studies on UV Cu ion lasers in conventional hollow cathode discharges.

A forced gas-cooled single-disk window using silicon nitride composite for high power CW millimeter waves

Silicon nitride composite as a candidate of a window material for high power CW (Continuous Wave) millimeter-waves was high power tested especially with a surface cooling by impinging gas nitrogen jets on the single-disk surface. Gas-cooling dramatically suppressed the temperature of the window disk even with gas flow rate of around 100 l/min. With gas cooling of 465l/min., 130kW CW power of HE11 mode could be transmitted through the silicon nitride window with a diameter of 88.9mm. The peak window temperature was completely saturated on 123.6 °C. Without gas-cooling it did not saturate and reached 323 °C during 30 seconds pulse. A possibility of 1MW CW single disk Brewster windows with a forced gas-cooling is discussed, resulting in convinced prospects of the windows with realistic size and thickness.

A compact, highly stable CW CO2 laser without brewster windows

We describe an open resonator, quasi sealed-off; 70cm cavity length CO2 laser with very high stability of power and frequency, which lases on 96 lines from 9R42 (2W) to 10P52 (5W) with a power of >11W on 9R20, 9P20, 10R20 and 10P20, plus on 18 hotband lines with ≈2W. This laser was used successfully to pump an FIR ring laser [1] enabling an FIR power stability of ΔP/P ≈ 10−4 by use of a simple PI control loop, thus demonstrating its superb frequency stability.

All-fiber Brewster windows made with extremely weakly fused asymmetric coupler

New type of fiber-optic Brewster windows made with extremely weakly fused asymmetric couplers is reported. The first polarization modulation waist point in the power transfer curve of the asymmetric coupler was taken as the stopping point in the coupler drawing process. A 20-percent power with 26.4-dB extinction ratio at the coupled port and a 80-percent power with 2.5-dB extinction ratio at the throughput port at the designated wavelength have been achieved, with the Brewster bandwidth being 38 nm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cw He-Kr+ laser with transverse radio frequency excitation

A cw He-Kr+ laser was excited with a capacitively coupled transverse radio frequency discharge. The laser was operated in a simple 40-cm active length alumina oxide tube which ends off via ceramic glass transitions in Brewster windows. Transformation of the laser discharge tube impedance to the 50 Ω output resistance of the rf source and symmetrization of the rf voltage were performed by a special matching network. cw lasing was obtained at 469.4, 458.3, 438.7, and 431.8 nm. The output power of all lines amounts to 35 mW at an input power of 600 W. The rms noise of the laser intensity did not exceed 0.6%.

Development of a tunable diode laser absorption spectrometer for measurements of the [formula omitted] ratio in methane

A tunable diode laser absorption spectrometer (TDLAS) for measuring the 13 C 12 C ratio in methane has been developed. Using a triple path arrangement the spectra of the CH 4 sample, a 13 CH 4 12 CH 4 isotope standard and pure 13CH 4 are recorded simultaneously and compared to evaluate the 13 CH 4 12 CH 4 ratio of the sample, using a 13CH 4 12CH 4 absorption line pair near 3007 cm −1. Systematic effects due to variations in temperature, pressure, and optical density were measured for this rotational-vibrational transition pair. Optical interference effects are effectively suppressed by linearly polarizing the laser beam and using Brewster windows for gas cells and detectors. The overall δ 13C accuracy vs. the PDB scale is about ± 1 ‰ for a CH 4 concentration of 2.5 % (sample size: 5 μmoles = 0.11 STP cm 3 CH 4) using 36 cm long absorption cells. The future application of a multipass cell should allow measurement concentrations of CH 4 down to about 50 ppm. The main advantages of the new method are the short measurement time of 10–15 min for one sample and the direct measurement on the CH 4 molecule without the need to chemically convert it to CO 2. With the present accuracy the new method should be useful for the measurement of CH 4 sources, allowing a greater sample throughput compared to the conventional mass spectrometry technique.

Operational efficiency increase in copper vapor laser due to the replacement of vacuum jacket Brewster windows with flat windows

The vacuum integrity of the discharge tube of a copper vapor laser (CVL) is normally protected by Brewster angled windows. In an attempt to increase the operating efficiency of the CVL, flat windows were used to replace the Brewster windows. Experimental data confirm that the overall efficiency of the CVL does increase when such windows are used. The experimental results are discussed in terms of a computer model found in the literature. The cause of the efficiency increase appears due to a double optical cavity set up by the flat windows. However, the variation of the efficiency due to changes in the pulse repetition frequency (PRF) and buffer gas pressure are less well understood.

The Influence of Sol-gel Glass Technology on Coherent and Partially Coherent Optical Imaging Systems

AbstractThis paper addresses developments in the understanding of intra-cavity elements in ion lasers using sol-gel prepared silica. Growing interest centres around the generation of coherent light in the near u.v. spectrum. Sol-gel silica offers unprecedented levels of purity and homogeneity for critical intra-cavity applications and may well solve the problem of creating colour-centre free Brewster windows for use in the u.v.We also report new work which makes use of the porous phase of such material and show how it is directed at one of the early bastions of photographic science – Lippmann's photography.

Calibration and service procedures for argon and krypton ophthalmic lasers

Aspects of the routine calibration and servicing of argon and krypton ophthalmic lasers are discussed. The function and service problems typically encountered with the various stages within each system—slit lamp delivery system, fibre-optic cable and coupling unit, aiming beam and shutter assembly, and the laser power generation unit—are described. Procedures outlined include the cleaning of optical surfaces such as the Brewster windows of the laser tube and its associated lasing mirrors. Also, more general aspects of calibration and performance assessment of such lasers are outlined. Consideration is also given to the clinical relevance of such procedures.

A powerful and stable CO 2 laser for CH 3OH FIR laser optical pumping

A CO 2 laser for optical pumping of a CH 3OH molecular laser has been developed. The laser design has the aims of high power [ $ ̃ 40W on the 9P(36) line], long-term stability (more than 30 min) and single-mode operation (TEM 00) at 20 MHz from the line centre. Operation with one and two Brewster windows and with different internal diameters has been achieved experimentally.