Lambda DG-4 / DG-5 Ultra High Speed Wavelength Switcher
The Lambda DG-4 offers unprecedented speed and versatility for experiments requiring rapid light wavelength switching. It offers all the advantages of interference filter-based systems, yet eliminates the temporal constraints imposed by filter switching devices. Switching between any two wavelengths is achieved in less than the 1.2 msec vertical retrace period of a video signal, allowing you to perform real-time video imaging. For dual wavelength ratio imaging studies, the Lambda DG-4 enhances your ability to follow fast changes in ion concentrations by acquiring a ratio pair in two consecutive video frames.
Narrow bandpass systems, such as single cavity interference filters, grating monochromators, and A.O. modulators, will, by their nature, pass harmonics of the desired wavelength. With variable wavelength devices, it is not always possible to obtain sufficient blocking of out-of-band wavelengths. Modern interference filters, as used in the Lambda DG-4, have integral blocking characteristics 1000 times better than typical monochromator systems. In addition, it is difficult to adjust the intensity of one wavelength relative to another in a traditional system with a single optical path and a variable wavelength device. The dual galvanometer design of the Lambda DG-4 eliminates this problem.
How It Works
This unique optical design of the Lambda DG-4 is based on dual scanning galvanometers. The wavelength selection is done by interference filters.
The standard version of the instrument, the Lambda DG-4, can host up to four 25mm interference filters. The Lambda DG-5, a five filter version with two 25mm and three 18mm filters, is also available.
The light coming from the 175W xenon arc lamp is focused on the first galvanometer mirror. The light is then directed, via a parabolic mirror, through one of the optical channels that may contain an interference filter. The light passing through the filter is collected by another parabolic mirror and focused on a second scanning mirror that directs it to a liquid light guide.
The light guide can be coupled to the illumination port of an instrument. (e.g. epi-illumination port of a microscope). The intensity of the output can be modulated by controlling the relative orientation of the two scanning mirrors. Thus this system can provide narrow band excitation at selected wavelengths over a range of intensities or can rapidly cut off the light source. Dwell time at any wavelength is arbitrarily set by the user. Transitions are achieved in less than 1.2msec.
Complete System for Wavelength Switching
A built-in 175 Watt ozone-free xenon arc lamp makes the Lambda DG-4 a complete excitation system and eliminates problems associated with device integration. Four or five interference filters can easily be installed in the DG-4 or DG-5, respectively. The light guide output from the Lambda DG-4 provides uniform spatial illumination, as well as vibration isolation from your microscope.
Integral Shuttering Function
The Lambda DG-4 provides a high speed shutter function with open/close times of 500µs. The shutter can be enabled between filter transitions to prevent light transmission through intermediate filters.
Intensity Attenuation Function
The light intensity can be adjusted by offsetting the output galvanometer such that light is not centered on the liquid light guide. Up to 15 logical filters can be defined with this method. Due to the scrambling effect of the light pipe, the output still has excellent uniformity. Direct insertion of neutral density optical filters is also possible in any of the four filter holders. A final neutral density optical filter can also be placed in the exiting light path which will reduce the light output from all 4 optical channels.
Two Outputs for Monitoring Filter Position
A 4 bit TTL signal transmits the current optical channel (filter) position. A digital-to-analog converter (DAC) output produces a voltage showing which filter is in use.
Computer control of the instrument is possible via parallel or serial port.