Dual Pulse-Length Laser Feedback Control for Stable Microsecond Pulses
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Solution Overview
Problem
Existing medical laser systems lack a simple and effective control system for delivering laser pulses in the microseconds scale, leading to unstable energy profiles and potential collateral thermal damage during subthreshold treatments.
Innovation Solution
A control system utilizing a beam splitter to divide laser pulses, a FPGA for real-time power feedback, and a two-step DAC algorithm to stabilize energy delivery, ensuring precise control of microsecond-scale pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If microsecond-scale laser pulses are delivered for subthreshold treatment, then selective photostimulation of pigmented cells is achieved, but thermal fluctuations and energy instability occur
Solution Approach 1:
The patent implements a feedback control system using a photodetector to monitor laser pulse energy in real-time. The measured energy is fed back to a control unit (FPGA) that adjusts the laser diode current to maintain stable pulse energy, thereby resolving the contradiction between achieving selective photostimulation and controlling thermal fluctuations.
Solution Approach 2:
The system dynamically adjusts the laser diode current based on real-time energy measurements. The control unit modifies operational parameters pulse-by-pulse to maintain stable energy delivery, enabling reliable subthreshold treatment while compensating for temporal energy variations.
2Object-affected harmful factors
If repetitive short subthreshold pulses are used to avoid cavitation or hemorrhage, then collateral thermal damage is reduced, but the control system complexity increases
Solution Approach 1:
The patent employs repetitive short laser pulses with controlled duty cycles to deliver subthreshold treatment. By delivering multiple low-energy pulses instead of a single high-energy pulse, the system achieves selective cell killing while allowing thermal dissipation between pulses, thereby reducing collateral thermal damage.
Solution Approach 2:
The feedback control system monitors and stabilizes the energy of each repetitive pulse, simplifying the control of multiple pulses by automatically maintaining consistent energy levels without requiring complex manual intervention for each pulse parameter.
3Measurement precision
If a fast feedback loop with several kV applied to Pockels cell is used to dampen spikes, then pulse stability is improved, but the system cost and complexity increase
Solution Approach 1:
The patent uses a feedback control system with a photodetector and FPGA to monitor and adjust laser pulse energy. This approach achieves pulse stability without requiring expensive high-voltage Pockels cells, instead using digital signal processing and current modulation to dampen energy spikes and maintain consistent pulse delivery.
Solution Approach 2:
The system replaces the mechanical/electrical approach of using high-voltage Pockels cells with a digital control approach using FPGA and photodetector feedback. This substitution reduces system complexity and cost while achieving comparable or superior pulse stability through software-based control algorithms.
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
Stabilizes energy profiles of microsecond pulses, reducing thermal fluctuations and enhancing the precision of subthreshold treatments.
Implementation Method 1
a beam splitter is provided in the optical path of the diode laser pump source module, the beam splitter dividing a laser pulse from the laser source into two portions; one portion of the laser beam pulse being transmitted to a target tissue; the other portion of the laser beam pulse being transmitted to a photodetector
Implementation Method 2
the other portion of the laser beam pulse being transmitted to a photodetector
Implementation Method 3
The '596 patent teaches laser pulse durations shorter than the thermal relaxation time of a target tissue in order to confine thermal damage in the target tissue only and to avoid collateral thermal damage
Implementation Method 4
The FPGA reads the feedback signal once every one to ten microseconds to compare measured power to selected power
Data Source
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AI summary
A single loop hardware-based system for producing laser pulses in a microsecond scale operational mode includes a GUI to enable a user to select the operational mode of the system; a laser source for producing one or more laser beam pulses, the laser source being a diode laser pump source module; a DSP which enables and disables a hardware-based FPGA. The FPGA controls the diode pump source module. A photodetector operatively connected to the hardware-based system measures the power of the laser pulse beam that was transmitted to the photodetector and, in a feedback mode, transmits a feedback signal of that power measurement to the FPGA.