Polyimide Windows Research Articles

Double‐Sided Indium Tin Oxide Photonic Crystal Glazing for All‐In‐One Multifunctional Rigid and Flexible Windows

AbstractFuturistic and high‐performance windows are required to perform multiple functions, occasionally including photo‐ and electricity‐associated functions. For each function, suitable components must be added, but this might result in complicated window structures that can impede the basic window function: high visibility. Therefore, platform technology is necessary to simplify window structures with minimal components for basic functions while adding specific desirable functions. This study proposes non‐close‐packed indium tin oxide (ITO) photonic crystals coated on both sides of rigid and flexible windows. Their photonic bandgap frequencies (stopbands) are tunable through the modulation of the ITO thickness or lattice constant, thereby manipulating the window light transmittances. When the stopband lies in bluelight (400–500 nm), the window can simultaneously block the bluelight and exhibit high transmittance (antireflection function) at 500–1500 nm. The dual functions are enhanced with double‐sided photonic crystal windows: the optical contrasts in solar irradiance transmittances (ΔTsol) between 500–1500 and 280–500 nm are maximally 37.1% and 47.2% for the glass and polyimide windows, respectively. Additionally, the windows can have dual stopbands. Moreover, the window stopbands can enhance the photoluminescence intensities of quantum dot films. This simplistic window is applicable to houses/buildings, automobiles, electronics, displays, and energy industries.

Deflection and Burst Properties of Polyimide Windows for High Pressures

Thin polyimide (PI) windows are used to contain gases in a variety of targets including National Ignition Facility ignition targets. Magnetized liner inertial fusion targets shot on the Sandia National Laboratory Z-facility and on the University of Rochester OMEGA laser facility typically contain deuterium gas in the pressure range from a few to as many as 15 atm, with the window diameters ranging from a few tenths of a millimeter at OMEGA to several millimeters at the Z-facility. These pressures are generally higher, with larger plastic deformations, than previously investigated. We have fabricated and assembled PI windows and measured their deflections and burst pressures for these pressure and diameter ranges at room temperature. The results are dependent on PI formulation and the details of the window assembly geometry. We analyze the scaling behavior of these higher-pressure windows similarly to but with an extension of the analysis of Bhandarkar et al. [Fusion Sci. Technol., Vol. 70, p. 332] and show that predictions of pressure-induced deflection using this analysis applies to a more complex window geometry than previously reported.

Inferring the electron temperature and density of shocked liquid deuterium using inelastic X-ray scattering

An experiment designed to launch laser-ablation-driven shock waves (10 to 70 Mbar) in a planar liquid-deuterium target on the OMEGA Laser System and to diagnose the shocked conditions using inelastic x-ray scattering is described. The electron temperature (Te) is inferred from the Doppler-broadened Compton-downshifted peak of the noncollective (αs = 1kλD > 1) x-ray scattering for Te > TFermi. The electron density (ne) is inferred from the downshifted plasmon peak of the collective (αscatter > 1) x-ray scattering. A cylindrical layer of liquid deuterium is formed in a cryogenic cell with 8-μm-thick polyimide windows. The polyimide ablator is irradiated with peak intensities in the range of 1013 to 1015 W/cm2 and shock waves are launched. Predictions from a 1-D hydrodynamics code show the shocked deuterium has a thickness of ∼0.1 mm with spatially uniform conditions. For the drive intensities under consideration, electron density up to ∼5 × 1023 cm−3 and electron temperature in the range of 10 to 25 eV are predicted. A laser-irradiated saran foil produces Cl Lyαemission. The spectrally resolved x-ray scattering is recorded at 90° for the noncollective scattering and at 40° for the collective scattering with a highly oriented pyrolytic graphite (HOPG) crystal spectrometer and an x-ray framing camera.

Plastic Deformation and Helium Permeation in Thin Polyimide Windows

Indirect-drive ignition targets require that the hohlraums contain a gas of helium, hydrogen, or a mixture of the two. For this purpose, thin polyimide windows must cover the laser entrance holes and any other hohlraum ports. We have fabricated, assembled, and tested such windows and have measured their deflection as a function of applied pressure. We also measured the permeation of helium through them. We find that the deflection is approximately linear with pressure and that the two polyimide formulations that we tested are internally consistent as well as consistent with the earlier data of Powell and Lopez when scaled for geometry. We also find that the permeation is linear with pressure, despite the large increase in window area-to-thickness ratio that occurs during a measurement run that results from the window deflection and thinning as the pressure increases. The permeability of our spin-cast material is 0.65 × 10-13 sccs/cm·Pa, with an uncertainty of 15% (sccs = standard cubic centimeters per second).

Thomson scattering from a shock front

We have obtained a Thomson scattering spectrum in the collective regime by scattering a probe beam from a shock front, in an experiment conducted at the Omega laser at the Laboratory for Laser Energetics. The probe beam was created by frequency converting a beamline at Omega to a 2ns pulse of 0.263μm light, focused with a dedicated optical focusing system. The diagnostic system included collecting optics, spectrometer, and streak camera, with a scattering angle of 101°. The target included a primary shock tube, a 20-μm-thick beryllium drive disk, 0.3-μm-thick polyimide windows mounted on a secondary tube, and a gas fill tube. Detected acoustic waves propagated parallel to the target axis. Ten laser beams irradiated the beryllium disk with 0.351μm light at 5×1014W∕cm2 for 1ns starting at to, driving a strong shock through argon gas at ρo=1mg∕cc. The 200J probe beam fired at t=19ns for 2ns, and at t=20.1ns a 0.3ns signal was detected. We attribute this signal to scattering from the shocked argon, before the density increased above critical due to radiative collapse.

In situ monitoring of polyimide windows for external ion microbeams

Damage of polyimide windows for external ion microbeams was monitored by analyzing backscattering protons from the window. A 1.5 MeV proton microbeam focused to approximately 50 × 50 μm 2 was transmitted through the polyimide window from vacuum to oxygen atmosphere. The changes in backscattering spectra of the window were monitored as a function of irradiation dose up to 2 × 10 18 H +/cm 2. For comparison, the polyimide window was irradiated in vacuum in the same way as the oxygen case. The backscattering spectra drastically changed in the case of oxygen. We observed that the carbon spectrum width, corresponding to the thickness of the window, substantially decreased with increasing the irradiation dose. The in situ monitoring of backscattering protons demonstrated the ability to detect the damage of the window and to predict the rupture of the window.

Thin-window high-efficiency position sensitive proportional counter for the vacuum flat crystal spectrometers on the Lawrence Livermore National Laboratory electron beam ion trap (abstract)

We have mounted 1 μm thick aluminized polyimide windows onto the position sensitive proportional counters employed by the wide-band flat crystal spectrometers at the Lawrence Livermore National Laboratory electron beam ion trap experiment. The aluminized polyimide, supported by thin wires across the short axis of the window, is used to isolate the detection chamber of the proportional counters, which operate at a pressure of 760 Torr, from the vacuum chamber of the spectrometer. The windows are modified versions of those developed for the proportional counters which were used during ground calibration of the Chandra X-ray Observatory. The transmission properties of these windows are, therefore, well known. The increased transmission efficiency of the polyimide windows relative to the 4 μm thick polypropylene window material previously employed by our proportional counters has extended the useful range of the spectrometer from roughly 20 to 30 Å at energies below the carbon edge, as well as increasing detection efficiency at wavelengths beyond the carbon edge. Using an octadecyl hydrogen maleate crystal with 2d=63.5 Å, we demonstrate the increased wavelength coverage by measuring the resonance, intercombination, and forbidden lines in helium-like N VII in two different density regimes. The thin polyimide windows have also increased the efficiency of the spectrometers entire wavelength range. To demonstrate the increased efficiency we compare the Fe XVII spectrum in the 15–17 Å band measured with the 1 μm aluminized polyimide windows to the 4 μm aluminized polypropylene windows. The comparison shows an average increase in efficiency of ∼40%. The polyimide windows have a significantly lower leak rate than the polypropylene windows making it possible to achieve approximately an order of magnitude lower pressure in the spectrometer vacuum chamber which reduces the gas load on the trap region.

DEVELOPMENT OF AN EXTERNAL MICROBEAM-PIXE SYSTEM USING THIN FILM WINDOWS

A external microbeam system using polyimide windows has been developed for PIXE (Particle Induced X-ray Emission) analysis in air. A beamline consists of a magnetic quadrupole-doublet lens, cylindrical objective slits and double-deflection scanning coils. Polyimide films with a thickness of 3.5 μm or 7.5 μm were used for the exit windows. Spot sizes in air were measured by beam-induced fluorescence of CsI scintillation plates. A minimum spot size obtained was about 10 μm for a 1.5 MeV proton beam. PIXE-mapping images of a Cu grid were successfully obtained in air.

Gas-Filled Hohlraum Fabrication

Los Alamos National Laboratory (LANL) researchers have fabricated and fielded gas-filled hohlraums at the Lawrence Livermore National Laboratory (LLNL) Nova laser. Fill pressures of 1--5 atmospheres have been typical. We describe the production of the parts, their assembly and fielding. Emphasis is placed on the production of gas-tight polyimide windows and the fielding apparatus and procedure.

The soft x-ray transmission properties of thin polyimide windows and their application to future detectors

The x-ray transmission properties of a very thin polyimide window in the range 7–310 Å have been investigated. The window is nominally 0.24 μm thick and is supported by a hexagonal polyimide grid. Transmission of over 60% and 80% at the oxygen Kα and carbon Kα lines, respectively, have been achieved. The use of such windows as the entrance window of a gas scintillation counter (GSPC) operating as a broadband spectrometer at XUV wavelengths is discussed. Overall detector efficiencies of greater than 10% for wavelengths less than 150 Å are possible to achieve.