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Plasma Light Source with Liquid Light Guide
Ø3 mm Liquid Light Guide
High-Power Plasma Light Source
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A hyperspectral imaging system built using Thorlabs' Cerna® Microscopy Platform, KURIOS-VB1 Tunable Bandpass Filter, and HPLS343 High-Power Plasma Light Source. For details, please see the Hyperspectral Imaging tab.
Thorlabs' HPLS343 and HPLS 345 high-power light sources are convenient and configurable illumination systems built around the long-lived and user-replaceable Luxim® Light Emitting Plasma (LEP)™ bulb module. These light sources are designed for long-term operation, and their optical output power is typically stable to 0.5%. Each is designed to optimally couple light from the bulb into a liquid light guide (LLG), which homogenizes the transmitted bulb emission and produces a uniform output light field. The broadband wavelength spectrum extends down to 350 nm and overlaps with the common DAPI, FITC, and TRITC filter sets used in biological imaging, which makes these sources well suited for fluorescence microscopy. In addition, the wide spectrum of these sources is important for hyperspectral imaging, as explained in the Hyperspectral Imaging tab, endoscopy, and other lighting and inspection applications.
Liquid Light Guides
These light sources use thermoelectric coolers to control the temperature of the LLG tip closest to the bulb, which extends the lifetime of the LLG. 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 bulb. Accumulated exposure to the UV portion of the bulb's specturm 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.
Optical Output Intensity
Front Panel Display
*Long Life Bulb Module: ≥10 000 hours
Thorlabs plans to offer replacement bulb modules for individual purchase in the future.
Mechanical Drawings of the HPLS343
The mechanical drawings of the HPLS345 differ from those of the HPLS343 only in the size of the LLG Port. This port on the HPLS345 is sized to accept the LLG05-4H.
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HPLS Series High-Power Plasma Light Source
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HPLS Series High-Power Plasma Light Source
|Graphs of Optical Intensity Measured at the Input and Output Endfaces of the LLG, Open and Closed Loop Operation, 48 Hour Duration|
External control of the light source is enabled by pressing the button labeled "External," which is located above the LCD display on the front panel of the instrument. After the button is pressed, it illuminates and stays illuminated while External mode is active. Enabling External control disables both software (PC) and front panel control, with the exception of the shutter. Both the shutter button on the front panel and software control of the shutter remain active for safety reasons; however, using one of these methods to toggle the shutter will automatically disable External control and return the instrument to Local control, in which the front panel and PC control are active.
External control of the light sources is performed by sending signals to a trio of female BNC connectors of the back panel of the instrument (Shutter Control, Analog IN and Trigger IN). The back panel also includes a pair of female SMA output connectors that provide access to status information (Analog OUT and Trigger OUT). Please see the Front & Back Panels tab for information about the Back Panel connectors.
The liquid cores of LLGs gradually become less transmissive with increasing exposure to UV light. As the Luxim® LEP™ bulb spectrum extends into the UV, the LLGs used to transmit light from these high-power 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 LEP bulb module 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 LEP bulb's light into the LLG.
While all of Thorlabs' standard Ø3 mm (Ø5 mm) liquid light guides are compatible with the HPLS343 (HPLS345), the LLG03-4H (LLG05-4H) are recommended for these light sources. These LLGs feature a yellow band near one end. The yellow band acts as a visual indicator that helps the user determine when the LLG is properly seated in the light source. When a 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 Figure 1. The LLG is fully inserted when the edge of the yellow marker ring is flush with the front panel, as shown in Figure 2. To remove the LLG, press up on the LLG Release switch and pull out the LLG, as shown in Figure 3. The light sources detect when a 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 a 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 section following Figures 1 through 3.
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 HPLS343 and HPLS345 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 a LLG with a high-power and broadband light source include:
The limitations of LLGs include a maximum operating temperature of 45 °C for long durations and 60 °C for durations of less than an hour. The HPLS343 and HPLS345 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. The LLG can operate indefinitely at temperatures below 45 °C. At higher temperatures, bubbles form in the liquid, which degrades the transmission properties of the LLG. These bubbles can be reabsorbed by the liquid if the temperature of the LLG exceeds 45 °C, but is no more than 60 °C, for less than an hour, and if the LLG is allowed to cool after being subjected to these elevated temperatures. We recommended a cool-down time of no less than 30 minutes. Temperatures in excess of 60 °C can result in permanent bubbles forming in the liquid, which 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 LEP bulb spectrum extends into the UV, the LLGs used with the HPLS 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, Teflon™, 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.
Liquid Light Guide Dimensions and Minimum Bend Radius:
|Active Core Diameter||Standard End Fittings||Protective Sleeve||Min. Bending Radius|
|3 mm||5 +0/-0.1 mm||20 ± 0.1 mm||9 ± 0.1 mm||24 ± 0.1 mm||7 ± 0.1 mm||40 mm|
|5 mm||7 +0/-0.1 mm||20 ± 0.1 mm||10 ± 0.1 mm||24 ± 0.1 mm||9.5 ± 0.1 mm||60 mm|
The drawing and photograph below illustrate the dimensions given in the table above. 180 ± 1° indicates the flatness tolerence between the metal and black material in the segment labled l2.
The user-replaceable Luxim® Light Emitting Plasma (LEP)™ bulb module at the core of the HPLS343 and HPLS345 is an intense source of full-spectrum white light and has a lifetime of at least 10 000 hours. A major contributing factor to its long life, which is ten times that of a xenon bulb, is a design that includes no electrodes and is strikingly different than the design of metal-halide discharge lamps and other conventional light sources.
The sketch in Figure 1 depicts the architecture of the LEP bulb module. Contained within the ceramic resonator are two antennas, and the sealed quartz bulb is positioned at the center. The bulb is contains a small amount of a halide salt mixture as well as inert and other gasses. The radio frequency (RF) driver is connected to the power input and feedback antennas using low-loss coaxial cables. When operating, the electric circuit generates an RF field, which is amplified and concentrated by the structure of the ceramic resonator. The bulb position coincides with the most intense region of the RF field, and the energy of the field ionizes the gasses and vaporizes the halides contained in the quartz bulb. The ionized gases transfer energy to the metal halide salts, which form an intense plasma column at the center of the bulb. This is the highly-efficient source of the intense full-spectrum white light. A reflective material located at the back of the lamp is used to direct all generated light into the forward direction.
In conventional metal-halide discharge lamp designs, a plasma is formed inside the bulb by transmitting a high-energy pulse across the two electrodes. Each pulse not only creates a plasma in the bulb but also vaporizes some of the electrode material, which both erodes the electrodes and deposits a metal on the bulb. This degrades the performance of the lamp and leads to its failure. In addition, the electrodes act as heat sinks that draw power away from the bulb. The driving energy applied to the bulb must be high enough to overcome these losses.
The LEP bulb module, by energizing a plasma arc without using filaments or electrodes, elininates all failure modes and inefficiencies of traditional broadband light sources, which results in an incredibly bright and stable source with long life span comparable only to light emitting diodes (LEDs).
The LEP bulb module is considered to be at the end of its life when, for a given driving current, the optical output intensity of the bulb drops to 50% of the intensity it produced when it was new. The bulb module package includes the ceramic resonator, quartz bulb, and heatsink. Replacing the bulb module package is a straight-forward procedure that can be performed by the user. Each bulb module has its own serial number that is read by the HPLS343 and HPLS345, and lifetime information for up to two bulb modules is stored in memory. This allows users to swap between two operational bulb units while preserving information about how long each has operated (the lifetime countdown).
An external host PC can control the operation of the HPLS343 and HPLS345 high-power plasma light sources. Users can choose to operate the source through a GUI or by writing and running custom programs. The drivers and software that enable both methods of control can be downloaded by clicking on the following link. An image of the GUI is shown in the image to the right and described in Chapter 7 of the manual, while the command-line language used to write custom programs is described in Chapter 8. Prior to running a custom program via the command-line interface, the downloadable drivers should be installed, the instrument should be powered on, and a USB cable should be connected between the host PC and the USB type B port on the back panel of the light source.
The basic command structure is a keyword, followed by an equals sign (=), followed by a character string, and terminated by a carriage return (CR). An example of a command is LAD=3 (CR), which sets the operation mode of the light source to Eco mode. The query command structure is a keyword, followed by a question mark (?), and terminated by a carriage return. An example of a query is LLG? (CR), which will return the temperature of the tip of the liquid light guide.
In hyperspectral imaging, a stack of spectrally separated, two-dimensional images is acquired. This technique is frequently used in microscopy, biomedical imaging, and machine vision, as it allows quick sample identification and analysis.
Hyperspectral imaging obtains images with significantly better spectral resolution than that provided by standalone color cameras. Color cameras represent the entire spectral range of an image by using three relatively wide spectral channels—red, green, and blue. In contrast, hyperspectral imaging systems incorporate optical elements such as liquid crystal tunable bandpass filters or diffraction gratings, which create spectral channels with significantly narrower bandwidths.
Thorlabs' Cerna® microscopy platform, Kurios® tunable filters, and scientific-grade cameras are easily adapted to hyperspectral imaging. The Cerna platform is a modular microscopy system that integrates with Thorlabs' SM lens tube construction systems and supports transmitted light illumination. Kurios tunable filters have SM-threaded interfaces for connections to the Cerna platform and our cameras. In addition, Kurios filters include software and a benchtop controller with external triggers, which enable fast, automated, synchronized wavelength switching and image capture.
Example Image Stack
The data in the images and video below demonstrate the hyperspectral imaging technique. Figure 1 depicts two images of a mature capsella bursa-pastoris embryo (also known as shepherd's-purse) taken with a Kurios filter set to center wavelengths of 500 nm and 650 nm. These two images show that an entire field of view is acquired at each spectral channel. Figure 2 is a video containing 31 images of the same sample, taken at center wavelengths from 420 nm to 730 nm in 10 nm steps. (10 nm is not the spectral resolution; the spectral resolution is set by the FWHM bandwidth at each wavelength.) In Figure 3, images from each spectral channel are used to determine the color of each pixel and assemble a color image. Figure 3 also demonstrates that a broadband spectrum is acquired at each pixel, permitting spectroscopic identification of different sample features within the field of view.
Kurios tunable filters offer a number of advantages for hyperspectral imaging. Unlike approaches that rely upon angle-tunable filters or manual filter swapping, Kurios filters use no moving parts, enabling vibrationless wavelength switching on millisecond timescales. Because the filter is not moved or exchanged during the measurement, the data is not subject to "pixel shift" image registration issues. Our filters also include software and a benchtop controller with external triggers, making them easy to integrate with data acquisition and analysis programs.
Figure 2: This video shows the image obtained from the sample as a function of the center wavelength of the KURIOS-WB1 tunable filter. The center wavelength was incremented in 10 nm steps from 420 nm to 730 nm. (10 nm is not the spectral resolution; the spectral resolution is set by the FWHM bandwidth at each wavelength.)
Below is a selection guide for all of our white-light, broadband illumination sources (or lamps). In addition to these sources, Thorlabs also offers an unmounted white-light LED, five white-light mounted LEDs, two white-light fiber-coupled LEDs, and three high-powered, white-light Solis™ LEDs.
|Lamp Selection Guide|
|(Click Representative Photo to Enlarge; Not to Scale)|
|Type||Plasma||Tungsten-Halogen||Tungsten||Globar||Tungsten-Halogen||Xenon Arc||Mercury-Xenon Arc||Tungsten-Halogen||Quartz Tungsten-Halogen||LED||Mercury Arc|
|Wavelength||350 nm - 800 nm||360 nm - 2600 nm||450 nm - 5500 nm||500 nm - 9000 nm||360 nm - 3800 nm||240 nm - 2400 nm||400 nm - 1300 nm||400 nm - 2200 nm||370 nm -
|340 nm -
|Output Coupling||Liquid Light Guide||Fiber Coupled (SMA),
Liquid Light Guide, or
|Free Space||Free Spacea||Fiber-Coupled Fiber Bundle||Free Space||Free Space||Liquid Light Guide|
|Output Power||4 Wb (Typ.)||7 Wb (Typ.)||10 mWc
|>1.5 Wd||>1.6 Wf||>1.3 Wf||1.4 Wg||50 mWh
|Not Available||Not Available|
|-||9 W||7.2 W||24 W||150 W||150 W||10 W||Not Available||Not Available|
|6000 Ki||2796 K||1900 K||1500 K||3400 K||5800 K||6000 K||3200 K||2800 K||Not Available||Not Available|
|Lifetime||10 000 hj||10 000 h (Avg.)||10 000 h (Avg.)||10 000 h (Avg.)||1000 hk (Avg.)||2000 hj||1000 to
10 000 h
to 50% Brightness
|2000 h||>25 000 h||>2500 h (Typ.)|
|QTH10B||Not Available||Not Available|
These sources are designed to be used with liquid light guides and can be controlled via front panel controls, a host PC, or by sending voltage signals to connectors on the back panel. Controls include the ability to continuously adjust the amount of light coupled from the bulb into the LLG and to independently toggle the shutter state. When a PC is used to control these light sources, the operator has access to commands and controls not accessible otherwise, including the ability to change the operation mode.
Each of the three operation modes is optimized for different application requirements. Open Loop mode, which is the default, drives the bulb module with current that is near the maximum specified current limit. This gives the user access to the maximum available optical output power, but does not attempt to stabilize the optical output power. Closed Loop mode uses a feedback loop to stabilize the optical output power at 80% of the maximum power achievable in Open Loop mode. Stabilization is performed by adjusting the current level driving the bulb module. Eco mode uses the Closed Loop feedback technique, but it stabilizes the optical output power at 50% of the power achievable in Open Loop mode. As Eco mode drives the bulb module at lower currents, the bulb is subjected to less heat stress; operation in this mode is expected to lengthen the lifetime of the bulb module beyond the typical 10 000 hours lifetime.
Thorlabs' Liquid Light Guides (LLGs) offer outstanding transmission from 340 nm to 800 nm for white light illumination applications. For large core diameters, liquid light guides are a more efficient transmission solution than fiber bundles as they eliminate the packing fraction loss (dead space) in the light fields transmitted by optical fiber bundles. For more information about LLGs, please see the LLGs tab.
The LLGs designed to be used with the HPLS343 and HPLS345 high-power plasma light sources feature a yellow band near one tip. The purpose of this band is to indicate when the LLG is inserted to the correct depth in the LLG Port of these light sources. With the exception of the yellow band, the LLG03-4H and
Thorlabs offers collimation adapters with AR-coated aspheric condenser lenses (EFL = 40 mm) for collimating the output from our High-Power Light Sources. Four different collimator housings are available; each is designed to mate to the illumination port on an Olympus IX/BX, Leica DMI, Zeiss Axioskop, or Nikon Eclipse Ti microscope.
These adapters quickly mount onto the end of either the Ø3 mm or Ø5 mm Liquid Light Guide (LLG). The LLG is secured via a setscrew into the back of the collimator. The addition of these adapters allows the user to incorporate our HPLS300 series lamps into a microscope illumination port.
|Olympus BX & IX
|Nikon Eclipse Ti
(Click to Enlarge)
|LLG Diameter||3 mm||5 mm||3 mm||5 mm||3 mm||5 mm||3 mm||5 mm|
|AR Coating||350 nm - 700 nm|
|Focal Length||40.00 mm ± 5%|
|Surface Quality||60-40 Scratch-Dig|