Dual fiber coupled laser-driven light source

Abstract

Laser-driven light sources (LDLS) have been gaining popularity in semiconductor metrology and spectroscopic measurement in the past 20 years because of their much higher brightness across a broad spectral range with higher stability than traditional electrode-based lamps. In addition, fiber-coupled LDLS systems offer more flexibility and convenience than free-spaced ones. However, due to the limited NA of fiber coupling optics, only light output from one side of a Xe plasma bulb is coupled to the fiber port, with light emitted into the opposite side of the Xe bulb wasted. To address this issue, a dual fiber coupling system is designed and implemented to collect the photons from both sides of a Xe plasma bulb. This paper will present the optical design of EQ-99 based LDLS lamp head with two fiber-coupled ports, the elliptical mirror alignment and optimization, and the performance of both fiber ports' output, including power spectrum, beam profile, and stability. Besides the total light power from two fiber ports being nearly doubled with the same laser power driver, the mirror coatings and output windows can be individually configured and optimized for different spectral ranges, which can be useful for broadband applications. One good example is its integration into the extended range CSE system to obtain a decent output flux covering 350 to 1100nm.