What is a Laser-Driven Plasma Light Source?

A laser-driven plasma light source (LDLS) is a high-brightness broadband light source that creates light by focusing a laser into a noble gas to produce a small, intense plasma. These sources are valued for their high radiance, stable output, and continuous spectral coverage from deep ultraviolet to near infrared. LDLS systems are commonly used in spectroscopy, imaging, and semiconductor inspection.

Plasma Ignition

Plasma generation in an LDLS begins with an electrical arc discharge that ionizes a small volume of noble gas, typically xenon or argon. This initial arc ignition creates a seed plasma. A high-power continuous-wave laser (>15 W) is then focused onto this region to sustain and stabilize the plasma by delivering continuous energy. The result is a small, stable, and spatially confined plasma that emits intense broadband radiation.

Plasma Temperature

The temperature of the plasma in an LDLS can exceed 10,000 K and may reach up to 20,000 K depending on the gas composition, laser power, and system configuration. These high temperatures result in strong blackbody-like emission across a wide range of wavelengths, particularly enhancing the ultraviolet output. The high plasma temperature is a key factor in the broad spectral performance of LDLS systems.

Plasma Size

The plasma generated in an LDLS is typically very small, with a diameter of less than 200 micrometers. This compact size contributes to the system’s high radiance and allows for efficient optical coupling into fibers or focused illumination systems.

Spectral Characteristics

LDLS systems produce a continuous spectrum spanning from below 200 nm in the deep ultraviolet (DUV), across the visible range, and into the near infrared (NIR), typically up to around 2,000 nm. The output resembles blackbody radiation with excelent UV performance due to the high plasma temperature. The small plasma volume also supports efficient optical coupling and high spatial coherence compared to other broadband sources.

Advantages Over Xenon Arc Lamps

While both LDLS and xenon arc lamps generate broadband light using a noble gas plasma, LDLS systems offer several distinct advantages:

• Higher Radiance: The laser-focused plasma in an LDLS is more compact and intense than an arc lamp, providing greater brightness for optical systems.
• Extended UV Output: LDLS deliver significantly more power in the deep UV (<250 nm), where xenon lamps are relatively weak.
• Improved Stability: LDLS offer superior temporal and spectral stability because they do not rely on electrodes, which degrade over time.
• Longer Lifetime: Without electrode erosion and with optimized thermal design, LDLS systems typically have longer operational lifespans of about 10.000 h while xenon arc lamps last only 400 – 2000 h.
• Better Coupling Efficiency: The point-like plasma source allows for efficient coupling into optical fibers or narrow acceptance angle optics.

Applications

LDLS are used in demanding applications requiring stable, high-brightness, and broad-spectrum light sources. Common fields of use include:

• UV/Vis/NIR spectroscopy
• Optical metrology and thin film measurement
• Fluorescence and hyperspectral imaging
• Semiconductor inspection
• Calibration of detectors and solar cells

With their unique combination of brightness, spectral range, and stability, laser-driven plasma light sources are a modern alternative to traditional arc-based broadband illumination systems.

Fiber Coupler for laser pumped plasma light source XWS-30