Fiber Coupled Integrating Sphere Laser Energy Meter Calibration
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Solution Overview
Problem
Current laser energy measurement systems face challenges in accurately measuring the averaged pulse energy of pulsed laser sources and calibrating commercial laser energy meters, particularly due to limitations in traceability to primary standards and uncertainties in time constant determination and pulse response characteristics.
Innovation Solution
The Fiber Coupled Integrating Sphere (FCIS) Based-Laser Energy Meter and Calibration System (FCIS based-LEMCS) employs a new configuration with two photodiodes and a series of choppers to measure averaged pulse energy and calibrate commercial laser energy meters, ensuring traceability to primary standards and improving reproducibility by adjusting Duty Cycles and repetition frequencies, and utilizing a DC motor with a rare earth doped magnet for higher frequency modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional laser energy measurement systems are used, then measurement capability is provided, but measurement precision and traceability to primary standards deteriorate due to uncertainties in time constant determination and pulse response characteristics
Solution Approach 1:
The patent introduces an integrating sphere as an intermediary device between the laser source and the photodetector. The sphere collects and uniformly distributes the laser energy across its inner surface, allowing the photodetector to measure the total energy without being affected by beam geometry or temporal pulse characteristics. This intermediary structure eliminates the need for precise time constant determination and improves traceability to primary standards.
Solution Approach 2:
The patent transitions from direct temporal measurement of laser pulses to spatial integration of energy across the sphere's surface. By converting the measurement from the time domain to the spatial domain, the system avoids uncertainties associated with time constant determination and pulse response characteristics, thereby improving measurement precision and traceability.
2Adaptability or versatility
If higher frequency modulation is used to extend measurement range, then frequency range improves, but device complexity increases due to need for DC motor with rare earth doped magnet
Solution Approach 1:
The patent replaces conventional mechanical chopping systems with a DC motor driven rare earth doped magnet system. The magnet modulates the laser beam at high frequencies without the mechanical wear and complexity of traditional chopper wheels. This substitution enables extended frequency range while actually reducing device complexity through more reliable electromagnetic actuation.
Solution Approach 2:
The patent changes the operating parameters of the modulation system by using rare earth doped magnets in the DC motor, which enables higher rotational speeds and thus higher modulation frequencies. This parameter change extends the measurable frequency range from conventional limits to above 1 MHz, improving adaptability without proportionally increasing complexity.
3Reliability
If two photodiodes are used instead of one, then measurement reliability improves through redundancy, but device complexity increases
Solution Approach 1:
The patent places photodiodes at specific locations on the integrating sphere where they receive uniformly distributed energy. Each photodiode measures a portion of the total energy, and their combined output provides the complete measurement. This local quality approach ensures that each detector operates under optimal conditions while maintaining system reliability through their combined measurement capability.
Solution Approach 2:
The patent uses two photodiodes to measure laser energy, which provides redundancy and improved reliability. While a single photodiode would suffice for basic measurement, the second photodiode ensures continued measurement capability if one fails and provides cross-validation of results, thereby improving reliability without excessive complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system enables precise measurement and calibration of averaged pulse energy with expanded uncertainty reduction, achieving high reproducibility and traceability, and extends the frequency range for accurate energy measurement and calibration up to 1 MHz.
Implementation Method 1
two photodiodes and a series of choppers to measure averaged pulse energy
Implementation Method 2
a series of choppers to measure averaged pulse energy and calibrate commercial laser energy meters, ensuring traceability to primary standards and improving reproducibility by adjusting Duty Cycles and repetition frequencies
Data Source
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AI summary
The averaged pulse energy (J) of a Pulsed Type Laser Source can be measured by several types of commercial laser energy meters, such as pyroelectric detector or thermopile sensor, the spectral responsivity and the time/frequency related response properties of which are compatible with those of the Pulsed Type Laser Source. These Commercial Laser Energy Meters, regardless of sensor/detector type, should be calibrated against the working standards calibrated in a national (or an international) traceability chain relying on primary standards on the highest level having the lowest uncertainty in realizations of the fundamental SI units. FCIS based-LEMCS designed in this invention accomplishes both of the above proficiencies of measuring the averaged pulse energy of the Pulsed Type Laser Source and calibrating the Commercial Laser Energy Meters, which are traceably to primary level standards. FCIS based-LEMCS contains an integrating sphere having a novel port and an interior design and a series of mechanical choppers having separate Duty Cycles, each of which is rotated by an electrical motor in FCIS based-LEMCS, used for generating a chopped type laser, called as Chopped Type Laser Source, in order to provide the reference and averaged pulse energy for traceable calibration of Commercial Laser Energy Meters. With this invention, in addition to generating the reference and averaged pulse energy to be used during the calibration of Commercial Laser Energy Meters to be performed by means of FCIS based-LEMCS, the peak pulse energies of the Pulsed Type Laser Source and the Chopped Type Laser Source, which is a strict part of FCIS based-LEMS and which is used for producing the reference averaged pulse energy in the calibration of Commercial Laser Energy Meters, are also measured by FCIS based-LEMCS, traceable to Electrical Substitution Cryogenic Radiometer (ESCR) in primary optical watt scale (W), to 133Cs (or 87Rb) Atomic Frequency Standard in time scale t (s), and to direct current unit (A) realized with Quantum Hall - primary resistance standard (ohm) and DC Josephson primary voltage standard (V). With this configuration presented as a preferred embodiment, the averaged pulse energy measurements are performed and achieved for a range extending from 16.5 p J to 100 mJ.