Purpose: To quantify the effect of distance on the irradiance and beam homogeneity from 4 curing lights.
Materials and Methods: Four light-emitting diode curing lights were evaluated: Fusion, Bluephase 16i, Demi and FlashLite Magna. The irradiance at the centre of the light beam (ICB) was measured at 1.0 to 9.0 mm from the emitting tip using a 3.9-mm diameter probe connected to a spectrometer. The uniformity of the beam from each curing light was characterized by means of the “top hat factor” at 2.0, 4.0, 6.0 and 8.0 mm from the emitting tip. The useful beam diameter, within which irradiance values were greater than 400 mW/cm2, was calculated. The ICB, top hat factor and useful beam diameter were compared by analysis of variance and Fisher’s protected least significant difference test at α = 0.01.

It’s time to buy another car. Like everyone else these days, you’re a bit cost-conscience, so you’re looking at getting the most for your money. You decide to see what the local used car lot has to offer. Before you get out of your car, the slick used car salesman approaches you, shoves a card into your hand and is a little too happy to help you find a new automobile. You approach a couple of cars that you think might fit your budget. The closer you get, you notice something that seems odd. You’re standing in front of two identical cars: same make, same model, same year, same color, even the same warranty. But you see that one is $5,000 less than the other. Hmm. The first, more expensive car seems to be in good order, looks nice, smells okay. You climb into the second car and it hits you why there is a difference in price: the second car has no dashboard instrumentation panel! No speedometer, no fuel gage, no warning lights.

The beam profiler magnification calibration involves measuring spot centroids for known beam position translations. This can be done either by moving the profiler or moving the spot. The former method is preferred since the profiler with magnification is usually mounted to a high quality 3-axis translation stage. For a 25x or greater magnification it is recommended to use a stage equipped with a differential micrometer capable of producing accurate and repeatable 1m steps.

 What is M²?

M², or Beam Propagation Ratio, is a value that indicates how close a laser is to being a single mode TEM00 beam, which in turn determines how small a beam waist can be focused. For the perfect Gaussian TEM00 condition the M² equals 1.

Ophir Photonics’ BeamCube is becoming popular as a one-stop product for measuring the performance of laser welding systems used in the manufacture of medical devices. Low to medium power laser weld parameters can be simultaneously measured, recorded, and monitored for compliance to federal requirements and previously set manufacturing limits. BeamCube uses a CCD camera, Thermopile sensor, and fast photodiode to measure the beam profile, average power. and spatial pulse profile of the welding laser.

Question: How can I be certain that my Beam Profiler is measuring accurately? Is there a standard calibration methodology?

Answer: There is no calibration standard from which one can verify their camera based beam profiling measurement accuracy. Spiricon has done the next best thing to provide customer confidence in reliable and consistent results from its camera based profilers. The issue can be broken down into two major areas; 1) the input (camera), and 2) the output (from software algorithms).

• Define Concept of Mode Quality
• Show What Happens in Process When Mode Changes
• Detailed Introduction to Beam Profiling Instrumentation
• Examples of How to Diagnose Processing Problems
• New Profiling Techniques

• THz Range available to the user
– Wavelengths and Frequencies
• Tools to Image THz beams
• Optics- Type and Sources
• Cameras and Other Sensors
• Results

CCD cameras are commonly used for many imaging applications, as well as in optical instrumentation applications. These cameras have many excellent characteristics for both scene imaging and laser beam analysis. However, CCD cameras have two characteristics that limit their potential performance. The first limiting factor is the baseline drift of the camera. If the baseline drifts below the digitizer zero, data in the background is lost, and is uncorrectable. If the baseline drifts above the digitizer zero, then a false background is introduced into the scene. This false background is partially correctable by taking a background frame with no input image, and then subtracting that from each imaged frame. ("Partially correctable" will be explained in detail later.)

The second characteristic that inhibits CCD cameras is their high level of random noise. A typical CCD camera used with an 8-bit digitizer yielding 256 counts, has 2 to 6 counts of random noise in the baseline. The noise is typically Gaussian, and goes both positive and negative about a mean or average baseline level. When normal baseline subtraction occurs, the negative noise components are truncated, leaving only the positive components. These lost negative noise components can distort measurements that rely on low intensity background.

Situations exist in which the baseline offset and lost negative noise components are very significant. For example, in image processing, when attempting to distinguish data with a very low contrast between objects, the contrast is compromised by the loss of the negative noise. Secondly the measurement of laser beam widths requires analysis of very low intensity signals far out into the wings of the beam. The intensity is low, but the area is large, and so even small distortion can create significant errors in measuring beam width.

The effect of baseline error is particularly significant on the measurement of a laser beam width. This measurement is very important because it gives the size of the beam at the measurement point, it is used in laser divergence measurement, and it is critical for realistic measurement of M², the ultimate criterion for the quality of a laser beam. One measurement of laser beam width, called second moment, or D4, which is the ISO definition of a true laser beam width, is especially sensitive to noise in the baseline. The D4 measurement method integrates all signals far out into the wings of the beam, and gives particular weight to the noise and signal in the wings. It is impossible to make this measurement without the negative noise components, and without other special algorithms to limit the effect of noise in the wings.

1. Introduction

There are many applications of lasers in which the beam profile is of critical importance. When the beam profile is important, it is usually necessary to measure it to insure that the proper profile exists. For some lasers and applications this may only be necessary during the design or fabrication phase of the laser. In other cases it is necessary to monitor the laser profile continuously during the laser operation. For example scientific applications of lasers often push the laser to its operational limits and continuous or periodic measurement of the beam profile is necessary to insure that the laser is still operating as expected. Some industrial laser applications require periodic beam profile monitoring to eliminate scrap produced when the laser degrades. In other applications, such as some medical uses of lasers, the practitioner has no capability to tune the laser, and the manufacturers measure the beam profile in the design phase to ensure that the laser provides reliable performance at all times. However, there are medical uses of lasers, such as photo-refractive keratotomy, PRK, wherein periodic checking of the beam profile can considerably enhance the reliability of the operation. PRK is an example of laser beam shaping which is a process whereby the irradiance of the laser beam is changed along its cross section. In order for this laser beam shaping to be effective, it is necessary to be able to measure the degree to which the irradiance pattern or beam profile has been modified by the shaping medium. This paper describes the general state of the art of laser beam profile analysis.1-14 It introduces the general need for beam profile analysis, methods for measuring the laser beam profile, a description of instrumentation that is used in beam profile measurement, a discussion of the information that can be obtained simply by viewing the beam profile, and finally, how quantitative measurements are made on laser beam profiles, and the significance of those quantitative measurements.