Frequently Asked Questions - illumination
LED Light Sources
The OptoLED can produce arbitrary pulse durations when driven by an external frequency generator.. So can the OptoFlash, but it ALSO has an internal timing circuit that can produce pulses anywhere between 50 microseconds and 100 milliseconds.
What the OptoLED has, and the Optoflash has not, are
1. Two channels rather than one (of course).
Yes, it's pretty straightforward. The only thing to bear in mind is that since both the diameter and radiation solid angle of the LED chip will be greater than a 100 micron fibre can accept, there will inevitably be a fair amount of light loss. However, a lot of light will still get through, and since the illuminated area at the other end of the fibre will be correspondingly smaller, the illuminated area is likely to be just as bright as you could get for direct illumination. Although you could in principle attach the fibre directly to the LED, in practice it's likely to b
In order to efficiently couple to a high Numerical Aperture (NA) objective lens, as required for epi-fluorescence measurements, it is crucial that the light is well collimated as it enters the back aperture of the lens. In order to achieve this with the appropriate magnification the light must come from a small point, historically an arc lamp which is a reasonable approxiamtion of a point source. Intense LEDs with emitters of approximately 1mm square work very well for this application.
"White" LEDs typically comprise of a blue LED with a peak at approximately 445nm which is coated with a broadband phosphor centered in the green section of the spectrum. Part of the blue emitted by the primary LED is absorbed and re-emitted at lower energy by the phosphor. This combination of blue primary and green / red secondary emission appears white to the human eye. Variants are sometimes described as cool white, neutral white or warm white reflecting respectively increased red output from the phosphor. For fluoresecence applications both the primary a
The OptoLED can switch wavelengths in approximately 100 nanoseconds; effectively instantaneously in terms of biological measurements. The Lite version has sub-millisecond performance which is sufficient for most applications.
The OptoLED controls two LEDs independently, and it also give a very stable optical output thanks to its optical feedback option. The LEDs can also be pulsed on and off extremely rapidly, with switching times on the order of 100 nanoseconds. LED intensity is controllable either by varying a continuous current, or by varying the lengths of high-frequency current pulses, or some combination of the two.
150W Lamps are less bright at lower/medium bandwindths with the Optoscan than with the specific 50W - 80W lamp that we recommend. For HBW >20nm then the 150W is better and we are happy to supply this, but in our opinion this defeats the purpose of a monochromator. Approximately 3 years ago Ushio developed an ultra-stable ultra-bright long-life lamp to operate at 50W. We sought permission to run these lamps at 75W - 80W and Ushio's engineers confirmed that this was within specification.
The Cairn Optoscan Monochromator has both an entrance and an exit slit, each having an independently settable width. The exit slit width, defines the bandwidth ONLY ASSUMING that the light passed into the monochromator is a beam of zero size. This has a maximum of 30 nm.
Up to 150W for the light source and 250W for the Optoscan monochromator system.
Arc light sources
Please follow the following procedure:
(1) Check that the bulb is well within its rated lifespan. The published figures are guidelines only so although a 400 hour lamp will usually last 500 - 600 hours, if a bulb does fail at 300 hours it probably just needs replacing.
(2) Disconnect the power cable from between the lamphouse and the power supply. Inspect the cable throughly at both ends and if any of the pins have become unseated then push them back and ensure that the cable is free from stress when replaced.
This does sound like a faulty power supply. Please contact us to arrange to have it returned and checked out. Please do not discard the "faulty" bulbs as they may well function correctly when the power supply has been repaired. Brand new lamps are easier to strike so if the fault is marginal then it can appear to be an issue with the bulbs.
Our microscope couplings have individual X-Y centering and Z focussing control on all LED and light guide input ports. For critical applications where it is vital that the light leaving the coupling is completely on-axis, or needs to be translated (e.g. a moving spot for photolysis) we can also add a tip / tilt control to the mirror cube. This is the same mechanism that we use for pixel alignment of two cameras in our TwinCam and can be fitted to any reflected port.