The Beam Irradiance on Target System (BITS) is a high energy laser (HEL) sensor array that directly measures the beam irradiance profile of HEL weapons. The BITS is a sensor array composed of 105 sensors arranged in a hexagonal pattern over a circular area and it is designed to withstand direct exposure to continuous wave (CW) lasers at threat irradiance levels. The sensor array spatially and temporally samples HEL beam profiles and is the only reusable and direct (on target) measurement system of its type. The BITS represents the state-of-the-art in directed energy test and evaluation HEL sensors.
Background
In October of 2012 the BITS system underwent its final acceptance test at the High Energy Laser Systems Test Facility (HELSTF) located in the White Sands Missile Range (WSMR) test complex where the system was exposed to over 20 HEL shots using the 20kW IPG laser at irradiance levels as high as 5kW/cm2, exposure times of ten seconds, and beam diameters of 2-5.6 cm (1/e2 diameter). The system provided calibrated truth data for the direct measurement of HEL exposure. To date BITS has undergone 74 tests under HEL conditions in outdoor environments, demonstrating that it is indeed a reusable and deployable system. Figure 1 is a photograph of the front of the BITS target.
How It Works
The BITS is composed of an array of optical collection cavities that are distributed across the sensor array. The sensor cavities are covered by a coated optics mirror that reflects the majority of the incident HEL light. One important advantage of the BITS is its ability to reflect the incident beam in a divergent pattern. This mitigates potential damage to anything in the path of the reflected energy which is important for the wide variety of test conditions that BITS will be exposed to.
The first generation BITS target has an array of 105 sensors laid out in a hexagonal pattern over a circular area with a diameter of 7cm and a sensor spacing of 6mm. The BITS electronics is a modular system and can support more sensor channels for future larger target needs. The sensor readings can also be recorded on board the target in a removable flash memory module. Figure 2 shows a cross section of a single BITS sensor.
Where It Stands
The BITS system has undergone multiple HEL tests and is being transitioned to HELSTF as the end user. Future potential uses of BITS include testing against the 100kW Joint High Power Solid State Laser (JHPSSL) at HELSTF. Other tests being discussed by the HEL test community will integrate the BITS on an Unmanned Aerial Vehicle (UAV) for testing of HEL systems.
This article was written by John Le Sage, Electrical Engineer, SemQuest Incorporated (Colorado Springs, CO). For more information, Click Here