2017 Workshop

This year’s delegates were treated to a slight change in format, with the morning dedicated to teaching and the afternoon reserved for practical sessions.  Between these sessions, we enjoyed a visit to the hospital restaurant to take advantage of some warm food, which some delegates enjoyed outside in the spring sunshine.

This year’s delegates had the opportunity to measure and calculate the attenuation of different lasers through various materials, to gain practical knowledge of laser safety eyewear calculations.

laser attenuation

Delegates also performed measurements of spectral and energy outputs from a home-use IPL as well as running through a rigorous Quality Assurance programme with a skin laser.

We were delighted to find that there was a (beautiful) variation in output when measuring beam profiles.  As you can see in the images below, there are some clear interference patterns towards the left of the image.

By working methodically through each optical component, we found that the positions of these patterns did not vary when changing the external optical components of the laser (i.e. twisting the fibre, replacing 10 mm optics with 12 mm optics), nor when moving the screen or ND filters.

We finally found that moving the TV lens on the beam profiler resulted in a change in the position of the artefacts:

TV lens rotated 15 mm

Feedback from the meeting was very positive, with some constructive comments (we’ll make sure we supply biscuits next time!) and some very kind comments too:

“Clear, concise explanations of the most important concepts regarding laser output measurements and clear demonstrations of how the measurements are performed in routine clinical practice”

“well structured and covered everything I was expecting”

“it was great to actually make some measurements and even better that they might be able to count towards some STP competencies”

“Well delivered lectures, engaging and passionate people”

2016 Highlights

We have further developed our method for measuring beam profiles, adjusting the optical arrangements to allow the setup to fit on a single retort stand. This simpler setup can be used in any clinical setting and yields interesting results:

Profiler setup 2016.JPG

Delegates carried out our weekly QC checks for the Pulsed Dye Laser in groups of four. One such check includes measurement of wavelength, as this has been found to vary in the past. On the day however, results were remarkably consistent:

PDL wavelength graph.png

 

NB: The nominal wavelength for the Pusled Dye Laser in question is 595 nm.  It typically varies between 598 nm (new dye kit) to 596 nm (old dye kit).  The peak seen here is at approximately 597.2 nm for groups A, C and D, and at 597.5 nm for group B.

 

2015 Beam Profile Measurements

We modified the setup this year to increase the distance between the beam profiler (camera) and the laser image (screen).  A distance of 4 m is enough to allow the lens we have to create a focussed image, but the final image only takes up a small area on the detector surface and therefore does not allow us to make the most of the equipment.

A better solution will be to employ a different lens, or at least to place the optical filters in front of the lens, rather than between the lens and the detector.

Despite these difficulties, we were able to extract some images showing cold-spots:

profile 1 profile 2

profile 3 profile 4

Although we determined that these were equally obvious to the naked eye by looking at the aiming beam.  When removing the damaged protective window (the cause of the cold-spot), everything looked fine to start with, although perhaps a little saturation was creating the appearance of noise:

profile 5 profile 6

After a bit of lunch, we tried the same again and found something more interesting:

profile 7profile 8

 

There is something here which can’t easily be seen by the naked eye.  Mr Atkins very kindly let us use his ZAP-IT paper for comparison:

ZAP-IT paper profiles

Although we are limited here by the scanning resolution, we can still see that the cold-spot is easily picked up on the ZAP-IT on the left, and there is some discrepancy on the right showing a slightly ‘colder’ region.  We all agreed that the beam profiler showed some more detail in this case, although the paper was much easier to use.

2014 NOHD calculations

A few people from the course asked if they could have a copy of the NOHD calculation that we carried out during the 2014 workshop.  For the lasers used at the workshop, the NOHDs extend well beyond the extent of the room.  For some, the NOHD exceeds the distance to the general public, 2 stories down (needless to say, we employ appropriate blinds over our windows!)

The excel file below contains the calculations and should automatically calculate NOHDs for you too, if you like.

Please do let me know if you plan to use this and acknowledge appropriately.  It has been peer reviewed, but there’s still likely to be a bug or two in the calculations.

calculating NOHDs

 

 

 


2014 Output consistency measurements

During our 2014 workshop, we measured the consistency of the output from the Pulsed Dye Laser.  Considering the ‘pulselet’ structure of a 40 ms nominal laser pulse, the groups consistently found the difficult-to-explain temporal pulse structure using a photodiode:

temporal output 40 ms.bmp
40 ms ‘pulselet’ structure

Output consistency over the course of a 1 or 2 minute treatment provided some interesting results, which are compiled in the following Excel file:

Output consistency measurements

And here’s one we did earlier.  This has been compiled for a forthcoming publication…

Output consistency over a range of laser systems

 

 

 


2014 Beam profiles

As promised, we have made available some of the data that delegates collected during the 2014 workshop.

Beam Profiles:

Each group took a slightly different approach to imaging the beam profile of the Pulsed Dye Laser.  In the most part, we wondered about the effects of imaging the beam in focus, or not; imaging from close to the beam axis, or from a larger angle and the effects of damage to the protective window on the image.

Group A imaged the defocussed beam at a distance of around 50 cm and compared this to the focussed beam:

at distance.bmp
defocussed beam
at focus.bmp
focussed beam

Group C compared the image obtained from as close the the beam axis as possible and from an angle >45 degrees:

straightish.bmp
close to axis
not straightish.bmp
imaging from an angle

We were all interested to find out whether the profiler was capable of determining hot or cold spots which might influence treatment.  Imaging was thus done using a damaged protective window on the laser end-piece (creating cold spots) and compared to an image taken with no protective window:

no window.bmp
no protective window
with window.bmp
with a damaged protective window
with window2.bmp
with a heavily damaged protective window