High-Power Xenon Light Sources with Liquid Light Guides

Click to Enlarge
These high-power light sources incorporate xenon short-arc lamps and feature LLG-coupled outputs.

Click to Enlarge
Click Here for Raw Data
The typical spectral power distribution for the SLS603 & SLS605 High-Power Light Sources measured prior to the LLG. The blue-shaded region indicates the -10 dB power operating wavelength range.

Features

• Output Spectrum: 380 to 780 nm
• Liquid Light Guide (LLG) Coupled Output
  • Compatible LLG Included with Each Source
  • Input Tip of LLG is Cooled Using Thermoelectric Coolers (TECs) to Extend LLG's Lifetime
• Independent Shutter Toggled via Automated and/or Manual Controls
• Location-Specific Power Cord Included

Optional Accessories

• Replacement Lamps
• Collimating Adapters for Microscopy
• Additional LLGs

Thorlabs' SLS603 & SLS605 High-Power Xenon Arc Light Sources with Liquid Light Guides provide stable illumination from 380 to 780 nm. The emitted light is coupled into a liquid light guide (LLG), which homogenizes the transmitted bulb emission and produces a uniform output light field. The broad output spectrum extends down to 380 nm and overlaps with the common DAPI, FITC, and TRITC filter sets used in biological imaging, making these high-power sources well suited for fluorescence microscopy. In addition, the wide spectrum of these sources is important for hyperspectral imaging, endoscopy, and other lighting and inspection applications.

The front panel of each high-power light source features controls and an LCD screen for full control of the source power, light intensity, shutter, and enabling or disabling external trigger inputs. The back panel features BNC connectors for external triggering and power modulation inputs, as well as a monitor output and USB port for computer control. The software GUI available for download on the Software tab offers full remote control mirroring the functionality available on the front panel. Command line operation is also available using USB connectivity and a terminal emulator or a user-created program.

Liquid Light Guides
The SLS603 and SLS605 high-power light sources are designed to couple light from the xenon lamp into the included LLG with a Ø3 mm or Ø5 mm core, respectively (the sources will not operate without a compatible LLG properly inserted). The advantages of LLGs include a transmitted beam free of dead spots, flexibility that allows them to be coiled, a large core size, and a high numerical aperture. Please see the LLGs tab for additional information. The Ø3 mm light guide provides a beam with higher brightness, while higher total power is coupled into the Ø5 mm LLG. It is possible to focus the beam from the Ø3 mm guide into a smaller spot, and under certain conditions this smaller core diameter may result in more power being coupled into a microscope. Coupling light from the endface of the LLG to a variety of microscopes can be enabled by using the collimation adapters available below. Thorlabs also offers LLG-to-SM1 adapters for both Ø3 mm and Ø5 mm core LLGs (Item #s AD3LLG and AD5LLG).

These high-power light sources use thermoelectric coolers to control the temperature of the LLG tip closest to the bulb, which extends the lifetime of the LLG. Also, the lamp in these sources is designed for continuous operation. It is advisable to refrain from frequent cycling of the lamp between ON and OFF states, as this may significantly reduce its lifespan. For optimal performance, it is recommended to allow 45 minutes to one hour for the lamp to reach thermal equilibrium after being switched on. It is recommended to use the shutter to turn the light output off and on instead of frequently powering the lamp off and back on. Closing the shutter during periods when the output emission of the light source is not needed will also extend the lifetime of the LLG, because this reduces its exposure to the UV radiation from the lamp. Accumulated exposure to the UV portion of the lamp's spectrum increases the attenuation of the LLG, and the LLG should be replaced when transmission levels drop below those required by the application. We recommend the LLGs offered below, which differ from our standard LLG offerings only in that these have a yellow band that acts as a visual guide that indicates when the LLG is correctly installed in the LLG Port of the light source.

Click to Enlarge
As shown above, the LLG is correctly installed when the majority of the marking ring is within the LLG port.

Liquid Light Guides for SLS603 & SLS605 Light Sources

The liquid cores of LLGs gradually become less transmissive with increasing exposure to UV light. As the xenon lamp spectrum extends into the UV, LLGs used to transmit light from these light sources will gradually become more absorptive with use. When the transmission properties of an LLG drops below usable levels, the LLG should be replaced. This will occur before the xenon lamp reaches its end-of-life. Closing the shutter during periods when the output emission of the light source is not needed will extend the lifetime of the LLG by blocking the coupling of the lamp's light into the LLG.

The dust cap on the output end of the LLG may burn if exposed to the intense light emitted by the LLG. To protect the LLG, and for safety, remove the dust cap before powering on the light source.

Installing and Removing a Liquid Light Guide

While all of Thorlabs' standard Ø3 mm (Ø5 mm) liquid light guides are compatible with the SLS603 (SLS605) light source, the LLG03-4H and LLG3-xH (LLG05-4H and LLG5-xH) LLGs are recommended. These LLGs each feature a yellow band near one end that acts as a visual indicator to help the user determine when the LLG is properly seated in the light source. When an LLG without the yellow band is used with these sources, it can be difficult to know when the LLG is correctly installed in the light source.

To insert the LLG, slide it into the LLG port as shown in the photo to the right. The LLG is fully inserted when the majority of the yellow marking ring is within the LLG port. To remove the LLG, press up on the Release switch and pull out the LLG. The light sources detect when an LLG is installed in the LLG Port. If there is no LLG present, the light source closes the shutter, and the shutter cannot be opened until an LLG is in place. This protects the user from exposure to the intense light emitted by the source.

To protect the tips of the LLGs from damage and to keep them as clean as possible, cover exposed LLG tips with their dust covers. Ensure that the tip of the LLG is free of grease, dust, and other contaminants before inserting it into the light source. For information on how to clean the tip, see the Cleaning section below.

Liquid Light Guide Overview

Click to Enlarge
Figure 4: Plotted are typical transmission data for a Ø3 mm core, 4' long LLG, with the recommended operation wavelength range shaded blue. As a function of length, only minimal variations (<2.3%) are expected between our 4' (1.2 m), 6' (1.8 m), and 8' (2.4 m) long liquid light guides.

Click to Enlarge
Figure 5: Plotted are typical transmission data for a Ø5 mm core, 4' long LLG, with the recommended operation wavelength range shaded blue. As a function of length, only minimal variations (<2.3%) are expected between 4' (1.2 m), 6' (1.8 m), and 8' (2.4 m) long liquid light guides.

A variety of applications benefit from the heat and vibration isolation achieved by routing the optical power output by a light source from a distant location to where it is needed. The SLS603 and SLS605 light souces have been designed to accept liquid light guides (LLGs) with Ø3 mm and Ø5 mm cores, respectively. LLGs are flexible light pipes fabricated from a polymer tube filled with a transparent, non-toxic, and non-flammable liquid. The tips of the tube are sealed with fused silica caps, which also act as optical end faces. Transmission through the LLG homogenizes the light field across the diameter of the core, which produces an output beam with uniform intensity. The many advantages of pairing an LLG with a high-power and broadband light source include:

• A Homogenous Transmitted Beam Free of the Dead Spots that Characterize the Light Field from a Silica Fiber Bundle
• The Ability to Coil and Arrange the LLGs, in Contrast to Silica Rods of Comparable Diameters that Break if Bent
• The Large Core Size and High Numerical Aperture of the LLG
• Excellent Transmission over the Entire Visible Spectral Range (Figures 4 and 5)

When used with the SLS603 and SLS605 light sources, the gasket of the LLG should not exceed 45 °C for long durations and 60 °C for durations of less than an hour. The gasket is indicated by the change in the fitting from chrome metal to a black color, as shown in the figure to the lower right. These LLGs are designed to operate at temperatures between -5 °C to 35 °C. The SLS603 and SLS605 light sources protect the LLG against excessive temperatures by monitoring the temperature of the tip of the LLG closest to the bulb, cooling the tip as required using a combination of thermoelectric coolers and fans, and powering down the light source if necessary. At higher temperatures, bubbles form in the liquid, which degrades the transmission properties of the LLG. If the temperature of gasket is between 45 °C to 60 °C for less than an hour, the bubbles can be reabsorbed by the liquid if the LLG is allowed to cool. We recommended a cool-down time of no less than 30 minutes. If the temperature of the gasket exceeds 60 °C, the LLG can be permanently damaged; the bubbles in the liquid will have a severe negative impact on the transmission properties of the LLG, and these high temperatures can also cause structural damage by degrading the seals between the various structural components of the guide.

LLGs, while flexible, also posses minimum bend radii. See the table below for the minimum bend radii of these LLGs. The tubes will develop permanent kinks if forced into a bend tighter than the minimum specification.

Reduction in Transmission with Exposure to Ultraviolet Light: The liquid in LLGs gradually becomes less transmissive with increasing exposure to UV light. As the xenon lamp spectrum extends into the UV, the LLGs used with SLS603 and SLS605 light sources will gradually become more absorptive with use. When the transmission properties drop below usable levels, the LLG should be replaced.

Cleaning the Optical End Faces of Liquid Light Guides: The fused silica, PTFE, and metal (either aluminum, chrome plated brass, or stainless steel) materials composing LLGs are resistant to common cleaning solvents; however, the tips of the LLGs should not be submerged in solvent, and neither should a heavily soaked cleaning pad be applied to the tip. Saturating the tip with solvent can result in the solvent penetrating the seal between the silica end face and the polymer tube and damaging the guide. If debris cannot be removed from the end face by wiping it with solvent, a razor blade, handled gently, can be used to clean the tip. If a razor blade is used, ensure that it does not chip the edge of the fused silica glass end face.

Figure 6: Diagram of an LLG Tip, with End Face at Left

Figure 7: End portion of an LLG with Key Dimensions Labeled.

SLS60x GUI Software

The SLS60x software GUI’s controls duplicate most front panel functions, including intensity adjustment, turning the light source on/off, opening and closing the shutter, and activating/deactivating the ports on the back panel.