Holographic film exposure time curves for common integrated light sensors

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See also the do it yourself kit incl PCB for a simple but reasonably accurate light meter.

This is an interactive interface for generating exposure diagrams for use with inexpensive and easily available integrated light sensors together with familiar holographic emulsions; these diagrams are ready to use and take all the relevant factors (like wavelength-dependent sensor and film sensitivities) into account.

In principle, the optimal values (which may also depend on developer, film age, etc) should be obtained by trial and error, starting from the these data as a first approximation. However, I found these values to be sufficiently accurate as they are, for the sensor/film combinations I tried out.  There is some considerable margin in the exposure time, so that some tens of percents of variation are hardly noticeable in the final hologram. Some crude estimates for tolerable margins (30%) are indicated by the dashed lines in the figures.

Explanation of the possible settings

Light sensors:

Most entries are for common, easily available light sensors that combine photodiodes with integrated amplifiers, and give an output voltage that is linear with the illumination over a wide range. Their sensitivity is just right for the intensities typically used in holography. They thus provide a cheap and extremely simple way to build photometers for holography with sufficient accuracy.

See here for a more detailed description of various monolithic light sensors, and a simple do-it-yourself circuit based on the familiar sensors OPT101/OPT202.

I added also an entry for the wide area PIN diode UDT PIN10-AP used with an external amplifier. This refers to my old-but-proven photometer circuit described here. Moreover, I also added an entry for the Thorlabs Silicon Power Meter S20MM.

Film types and wavelength:

Pretty much self-explaining. More emulsion types can easily be added upon request. For the Slavich products the center line corresponds to the illumination density associated with the highest diffraction index, as listed in their data sheet (corresponding to optical density OD=2, approx).

Reference beam incidence angle:

When the reference beam hits the film plane at an angle (typically the Brewster angle, which is ca 56 degrees with respect to the normal), the actual intensity per square cm on the film plane is less (by a factor of 1/cos(alpha) = 0.55) than what a light sensor aiming straight into the reference beam suggests. Thus we provide an option for automatically taking this factor into account. Obviously, for holograms with perpendicular reference beam, the zero degree incidence angle option should be chosen.

We consider the reference beam because it is stronger than the object beam. The readings need to be modified if one has a high object intensity. For zero incidence ref beam angle, simply add the average object beam mV reading to the ref beam reading. For 56 degree ref beam angle, add twice the object beam mV reading; in particular, for the usual 1:4 object/ref beam intensity ratio, add 50% extra to the mV reading of the sensor.

Example 1 - transmission hologram (using the default settings above)

Assume you use a TSL250R at 633nm with a PFG-01 film, and when aiming into the reference beam at Brewster angle, you get a reading of 1V. If the object light is very weak, then the exposure time should be around 26sec. If the object intensity is, say 250mV (so you have a 1:4 ratio), then you add twice this value to the reference beam value, which makes 1.5V. From the diagram you see that the exposure time should be around 17sec.

Example 2 - Denisyuk hologram

Assume you use an OPT202 at 532nm with an Ultimate 08 plate, with a single beam setup where the reference beam hits the plate at near right angle. Assume that when aiming into the reference beam, you get a reading of 80mV while the object light gives 20mV. From the diagram you see that the exposure time for 100mV total should be around 90sec.

Example 3 - H2 image plane reflection copy from transmission master

Assume you use an OPT301M at 514nm with an Ultimate15 plate, with a reflection setup where the reference beam hits the plate at the Brewster angle, and the real object image intersects the plate. The intensity of the object light will thus be much higher as for a transmission setup, and my rule of thumb is to find the brightest spot and aim for a reference/object ratio of 1.5-2 at this spot. In a concrete example, the maximal object intensity was 80mV and the reference was 170mV. So alltogether we count 2x80+170=330mV, which yields approx 6s exposure time according to the diagram. These are the actual data that were used to create the ultra-bright reflection copy shown here.

Note added:

I made some precise measurements and found that all detectors I used (TSL250R, TSL251R, OPT101, OPT202, OPT301M, UDT PIN-10) gave consistent answers within 20%. Specifically, for the sensor OPT301M and film VRP-M developed with JD-2, I achieved an optical density of OD=2 right on the line of the relevant plot (and OD=1 on the dashed line to the left) - precisely as it is supposed to be !