Photons flux density

Figure 19. PMC potential and photocurrent-potential curves for an Si-MOS device (2 nm Si02) at different photon flux densities (indicated for photocurrents).

Fig. 1. Rates of CO2 assimilation, A (/miol s ) leaf conductance, g (mol m s ) intercellular partial pressure of CO2, Pi (Pa) soil water potential and leaf water potential, xp (MPa) during gas-exchange measurements of a 30-day-old cotton plant, plotted against day after watering was withheld. Measurements were made with 2 mmol m sec" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure difference between leaf and air (S.C. Wong, unpublished data).

Fig. 2. Rates of CO2 assimilation,. 4, and leaf conductances, g, as functions of intercellular partial pressure of CO2, p in Zea mays on various days after withholding watering. Measurements made with 9.5,19.0,30.5, and 38.0 Pa ambient partial pressure of CO2, 2 mmol m" s" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure differences between leaf and air. Closed symbols represent measurements with 30.5 Pa ambient partial pressure of COj. Leaf water potentials were 0.05, - 0.2, - 0.5 and - 0.8 MPa on day 0, 4, 11 and 14, respectively (after Wong et al., 1985).

Procedure Chlorophyll was excited for 2 sec by actinic light with a photon flux density of 200 mmol m 2 s Prior to measuring the chlorophyll,... 

Observations The apparatus allows the adjustment of excitation time to 4 sec or longer. Also, photon flux density of 200gmol m2 s 1 can be elevated to 400 or 600 gmol m 2 s, which depends on plant species or measuring conditions. 

Nonlinear light-matter interactions have been successfully applied to create new visualization contrast mechanisms for optical microscopy. Nonlinear optical microscopy employs femtosecond and picosecond lasers to achieve a high photon flux density by focusing the beam onto a sample with a high numerical aperture (NA) microscope... 

Monson, R. K., A. J. Hills, P. R. Zimmerman, and R. Fall, Studies of the Relationship between Isoprene Emission Rate and C02 or Photon-Flux Density Using a Real-Time Isoprene Analyzer, Plant Cell Environ., 14, 517-523 (1991). 

To complete the two-photon transition, the two photons must arrive at the absorber within the virtual state lifetime r. For classical uncorrelated photons the probability of accidental overlap increases with photon flux density. Therefore excitation by short, tightly focused laser pulses is needed for the TPA. Probabilistic analysis gives the two-photon transition rate ... 

The two contributions have different dependencies on the photon flux density. Eor entangled photons the TPA rate is proportional to the flux density, whereas for classical photons it is proportional to the square of the flux density. These dependencies result in two different exposure regimes depending on the photon flux density. The critical photon flux density, separating these regimes is defined using the condition R = R2 ... 

Photon flux density and the average power of the incident beam were varied in a wide range that exceeded the current possibihties. Highest estimates of the photon-pair yields from SPDC sources, given in the hterature, are in the megahertz range [74]. Therefore we assiune an overestimated pair rate of 10 s which corresponds to the photon flux density of 4 x 10 cm s for a circiflar area with diameter of 0.8 pm. 

Figure 16 illustrates that the model source providing an entangled photon pair rate of 10 s and photon flux density of x 10 cm s in the area... 

Fig. 17 TPA and single-photon absorption rates versus incident photon flux density calculated using parameters from Table 1 for the case of excitation by pulsed SPDC soimce. Diameter of the irradiated area is 0.8 xm. The dashed lines emphasize the photon flux density and the entangled photon TPA rate provided by the model source...

Cucumber seedlings (Cucumis sativus Long Green Improved ) were grown in a growth chamber maintained at a temperature of 25°C and a photon flux density (PFPD) of 200 pmol s"1 m 2 continuous illumination. Electrolyte leakage induced by compounds was determined using 4 mm cotyledon discs as described by Kenyon... 

Two-photon excitation of a fluorescent within the cross section of the day molecule about 10 16 cm2, is an induced probe for time about 10"15 s by laser light in the visible or near UV spectral range (Denk et. al., 1990). Such an excitation requires instaneous photon flux densities ofthe order of 1031 photons/cm2. 

For many purposes in plant studies, it is important to know the photon flux density. For instance, the rate of photosynthesis depends on the rate of absorption of photons, not on the rate of absorption of energy. Some instruments are sensitive only to photosynthetically useful photons (e.g., wavelengths basically from 400 to 700 nm), the so-called photosynthetic photon flux (PPF) or photosynthetic photon flux density (PPFD), both of which are expressed in jimol m-2 s-1 (Fig. 4-4b). 

Fluencerate is the fluence per unit time,e.g., the photon fluence rate (mol m-2 s-1) is thesameas the photon flux density. 

Relative photon flux density per unit wavelength interval... 

C. A certain optical filter, which passes all wavelengths below 600 nm and absorbs all those above 600 nm, is placed over a radiometric device. If the meter indicates 1 W m-2, what is the maximum photon flux density ... 

A. What is the minimum photon flux density in pmol m-2 s-1 at 680 nm ... 

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