Zoya M. Semichastnova

Femtosecond streak tubes designing, manufacturing, and testing

New generation of streak tubes intended for single-shot and synchroscan operations with femtosecond time resolution was computer modelled, designed, manufactured, tested and adopted for further application in laser research. The developed PV-FS type tubes provide close to 100 fs-time resolution in single-shot streak mode. It is important to note that the PV-FS tubes may be equipped with Peltier cooled S1-photocathodes and their spectral sensitivity may cover the range of 115 - 1550 nm. The developed photocathodes have very low surface resistance (tens of Ohm per square unit). New tubes offer a high (more than 50 line pairs/mm) spatial resolution when recording ultrafast optical images with femtosecond time resolution. Due to keeping the PV-FS external geometry similar to the well-known PV-type tubes it becomes possible to install new devices into available streak cameras (AGAT, Imacon 500, etc.).

Dynamic parameters evaluation for femtosecond streak tubes

Presented are the experimental results on femtosecond streak tubes measurements in dynamic mode. Several streak tube prototypes have been manufactured, with either distributed coaxial-strip line or capacitor-type photocathode-accelerating mesh assembly. Electrical field transition time in the photocathode-accelerating mesh gap was investigated. Tubes have been tested in a variety of regimes, in order to define the most efficient ones. Dynamic parameters of the developed femtosecond streak tubes were measured inside the streak camera prototype. The following dynamic parameters were evaluated: ultimate time resolution, dynamic range, and signal/noise ratio, spectral range, input sensitivity, streak speed and its nonlinearities, etc. The developed and optimized femtosecond streak tubes represent a reliable basis for design of streak cameras being required for photographic recording of ultrafast events in laser and plasma physics, time-resolved spectroscopy, laser interaction with matter, laser fusion, etc.

Sub-100 fs streak tube: computer-aided design, manufacturing, and testing

In the present communication we describe the design of the sub-100 fs streak-tube that may be used for commercial streak cameras manufacturing. Careful attention is paid to preparing of a very smooth input photocathode substrate on which a low surface resistance (1-5 Ohm/) photocathode of S-1 type is deposited. Our estimations have shown that the photocathode surface roughness of about tens of nanometers may restrict the ultimate time resolution at the level of 100 fs. This is the reason why the photocathode substrate surface has to be smooth within the units of nanometers. The curvature of the photocathode surface is also very important to compensate the difference in the time-of-flight of electrons emitted from the central and peripheral photocathode areas. Further modernization was conducted with a photocathode-accelerating mesh assembly. The assembly may operate with 2 - 3 ns (FWHM) electrical pulses of 12 - 15 kV amplitude. In order to improve the S/N ratio in the streaked images, a shuttering system was incorporated inside the tube. As the result, a completely new femtosecond streak tube of PV-FS-M type was designed, manufactured, and tested.

Large photocathode area picosecond streak tube

The paper reports on the development of a new streak image tube with accelerating mesh and large (18 mm) photocathode work area. The tubes temporal resolution is close to one picosecond. To govern photoelectronic images the tube possesses shutter and deflector plates. Its geometric design allows uniform spatial resolution (more than 25 lp/mm) along the entire photocathode work area at 1.3 electron-optical magnification and negligibly small distortion. Being a continuation of the well-known PV and PIF - type streak image tubes developed in due time in GPI, the tube represents a promising tool for taking pictures of ultrafast processes in wide radiation spectrum range.

Small-Size Meshless 50 ps Streak Tube

In contrast to the conventional image intensifier with large work area, a streak image tube should possess additional important feature - the comparatively small temporal distortion at the entire work area of the photocathode. With this additional engineering restriction taken into account, a novel small-size meshless streak image tube has been developed by means of numerical optimization. The tube with 25-mm wide work area contains a pair of deflection plates to sweep the electron image along the 25 mm output phosphor screen that is separated by 100 mm from the photocathode. The electron image can be shuttered with a 300 V blanking electric pulse. Electron-optical magnification of the tube is unit; spatial resolution reaches 30 lp/mm over the entire photocathode work area; temporal resolution lies in the 20 - 50 ps range, depending on the accelerating voltage (6 - 15 kV).

Investigation on EBI and secondary electron emission in streak tubes

The investigations of residual gas influence on EBI in streak tubes were continued. Model of the microdischarges in streak tubes, grounded on the theory of reciprocal ion emission is considered and it was shown, it is agree with experimental data on EBI fluctuations. The secondary electron emission from a material of an anode diaphragm was detected and investigated.

Experimental studies on residual gases and EBI in streak tubes

The composition of residual gases in streak tubes has been measured. The outgassing at supply of electrical voltage to the streak tube, at heating of Cr2O3 layer and at glass melting were investigated. The EBI fluctuations at pressure of 2 X 10-8 Torr and 10-6 Torr in streak tubes were examined.

Research and development on femtosecond cameras and diffractometers

Current GPI status on femtosecond cameras and diffractometers research and development is overviewed. Discussed are the key components of the femtosecond diffractometer which is now under design. The first experimental prototype of 20 - 40 kV, femtosecond photoelectron diffractometer is computer designed, manufactured and tested.

Streak tube designing in GPI

A variety of streak/framing/synchroscan image tubes are now under design and manufacturing in the Department of Photoelectronics, General Physics Institute. Among them are: a series of the well-known PV001 image tubes introduced into wide practice since 1978, a set of more advanced PIF001 tubes originally designed in 1979, specially developed femtosecond streak tubes of BSV-type, which were initially proposed in 1987, and finally a number of PF-type tubes placed in service last year. The whole set of these image tubes may cover the spectral range from 115 nm up to 1.55 micrometers , providing maximum sensitivity of 0.5 (mu) A/W at 1.55 micrometers (S1/IR) and up to 3 mA/W at 900 nm (S25/ER). Various input photocathode windows may be used: fiber-optics or borosilicate substrates which blue transparency starts at 350 nm. UV-glass windows (> 200 nm), MgF2 input window (> 115 nm). All tubes with photocathode- accelerating mesh geometry have photocathode area of 6 mm in diameter, while the tubes in non-mesh configuration (PV and PF0 have a rectangular photocathode area of not less than 4 mm by 18 mm. The described tubes may be supplied with any type of phosphor screen (red, orange, blue, green) deposited onto fiber-optics faceplate.