Specifications

Brief overview of specifications

- - Repetition rate: DC to 5 kHz
  - Pulse duration: variable between about 20 microsec and multiple millisec, up to continuous
  - Nozzle diameter: typically 150, 200 , 300 and 500 micrometer; other diameters on request
  - Nozzle shape: conical with 40 degrees opening angle or straight channel; rectangular micro-fabricated de Laval shape
  - Backing pressure: 0 to 10 Bar max (depending on nozzle diameter); typically 0 - 5 Bar
  - Operating temperature: typically room temperature

Full scientific reports

- - A short pulse (7 μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams, Review of Scientific Instruments 80 (2009), 113303 (pdf link)
  - In situ characterization of a cold and short pulsed molecular beam by femtosecond ion imaging , Physical Chemistry Chemical Physics 11 (2009), 3958 (pdf link)
  - Measurement of the density profile of pure and seeded molecular beams by femtosecond ion imaging, Review of Scientific Instruments 86 (2015), 023110 (pdf link)

Operating principle

Rotational temperature

The Amsterdam Piezo Valve is able to produce very cold seeded molecular beams. The rotational temperature of polyatomic molecules seeded in Neon at moderate backing pressures of about 4-7 Bar is typically around 1-1.5 Kelvin. See below a hexapole focusing spectrum of a pulsed molecular beam of CH3Br with either the Amsterdam Piezo Valve or the Parker (General) Valve (solenoid magnetic plunger type).

Pulse width

The Amsterdam Piezo Valve is able to produce short and intense pulses of gas. Depending on the carrier gas pulses with a FWHM of 10-20 microsec can be obtained. Below a graph is shown detecting NO+ ions after ionization with a nanosecond laser of two different skimmed and seeded beams of 0.1% NO in Helium and Neon. The delay between the laser firing and the valve trigger was scanned.

Beam density and brightness

(A) From gas load and pump speed measurements

(B) From measured beam density by Femtosecond Ion Imaging

In experiments by Congsen Meng and Maurice Janssen at LaserLaB VU Amsterdam the absolute beam density of a pulsed beam of Xe produced by the Amsterdam Piezo Valve was measured. The results using the novel technique of femtosecond ion imaging were published as:

Congsen Meng and Maurice H.M. Janssen, Measurement of the density profile of pure and seeded molecular beams by femtosecond ion imaging, Rev. of Scientific Instruments 86 (2015), 023110 (pdf link).

In the absence of skimmer interference we conclude that a pulsed expansion of 1 Bar Xenon results in a center line beam density of about 6*10¹³ cm^-3 at a position 16 cm downstream of the nozzle opening.

(C) Skimmer interference

One of the key findings from this 2015 RSI research in Amsterdam was that these pulsed molecular beams are so strong that careful consideration of the effects of (small) skimmers is needed. It was observed that the measured density at 16 cm downstream of the 200 micrometer nozzle was attenuated by a factor of 50-100, by using small skimmers of 1-1.5 mm diameter at relatively close distances from the nozzle.

Subsequent detailed simulations by Prof. Uzi Even confirmed quantitatively our findings, see the graphs below (unpublished calculations courtesy of Prof. Even, private communication). Shown are the density and temperature profile of an expansion with an initial density of 2*10²¹ m^-3 (= 2*10¹⁵ cm^-3), representing our measured density of a 1 Bar Xenon beam from a 200 micron nozzle, passing a 1.5 mm diameter skimmer located 3 cm downstream from the nozzle opening. These calculations by prof. Even show that the Xenon beam transmission through the 1.5 mm skimmer is reduced by a factor of 50.

This means that the high initial density results in strong skimmer interference and it is recommended to use large opening skimmers (4 mm) that are located at sufficiently large distances from the nozzle (> 8-10 cm) to avoid these effects on supersonic beam transmission and temperature.

For a full discussion of the effects of skimmer interference in strong pulsed expansions see the following publication:

U. Even, Pulsed Supersonic Beams from High Pressure Source: Simulation Results and Experimental Measurements, Advances in Chemistry (2014), 636042 (pdf link)

Density map for a beam of Xenon atoms with initial density of 2*10¹⁵ cm^-3 entering a skimmer with opening diameter of 1.5 mm. Unpublished calculations, courtesy of prof. U. Even.

Density along the center line for a beam of Xenon atoms with initial density of 2*10¹⁵ cm^-3 entering a skimmer with opening diameter of 1.5 mm. Unpublished calculations, courtesy of prof. U. Even.

Temperature map for a beam of Xenon atoms with initial density of 2*10¹⁵ cm^-3 entering a skimmer with opening diameter of 1.5 mm. Unpublished calculations, courtesy of prof. U. Even.

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