it is a long post i guess and i will be glad if anyone can answer all of my questions please.
i have come to understand that their are 3 parameters which effect the laser removal efficiency
now about the joules - the higher the better , right?
about the spot size - it effect the penetration depth of the laser beam into the skin . now if my hairs have short follicle that means the i need to be treated with smaller spot size with higher joules , or will it have better effect treating with higher spot size (which means that the effective power will spread into deeper are , don’t i get less energy that way?)
about the pulse width - less is better but still it depends on the hair size , anyone can explain this parameter?
last question, if the hair grow in cycle , how many percent of hairs are in the anagen stage every time? when i get laser treatment it means that the hairs which were in the catagen/telogen stages weren’t effected at all? (although the upper cells can be effected not the bulb…)
if that is so , then it is ideal to get a treatment as soon as you have the most anagen hairs on each body part… when that happens? if i wait a long time like 3 month , 4 month between each treatment will the anagen rate will change for worse / better ? what about 6-8 weeks between each session , doesn’t it causes to have more anagen hairs ?
sorry for the long post , i am just trying to understand how to get the best results i can have (so far i had 6 treatments and its not satisfying…)
what machine have you been using for your 6 treatments and at what settings? what area are you treating with what type of hair and skin? settings are dependent on these factors as well.
in short, large spot size, short pulse, and higher joules are more effective in most cases. you can search for sslhr’s posts to read in detail how and why. he explains it well.
lagirl , just to understand , you got treated with 18mm and 20j and then went to 15mm 30j , why is that if bigger spot size is better? and besides according to sslhr the effective energy is pretty much the same : 202.543 = 50.868 , 301.766 = 52.987 , so i would like some focus on that please if you can…
i have dark hair and light skin. my hair on my belly , chest , shoulders and upper hand are coarse and dark . my hair on my back is dark and fine. when i begin the treatments i had hairs all over this areas so it wasnt induced from the laser treatments…
on my chest and belly i have used the lightsheer with this settings from what i remember : 30ms (default? ) pulse width , started with 24j and in my last treatment they used 32j or 34j. every treatment hurt alot and i dont know if i could go up on the joules… last two treatments i didn’t have full shadding on this area. so i am thinking on moving to alexandrite.
on my upper hands / shoulders i started with the lightsheer for 4 treatments with probebly the same settings as the belly and chest , also 30ms pulse width. everytime i had shadding.
in my 5 treatment i switched to the arion alexandrite laser (posted a link to its specfications in another post of mine) and got treated with the scanner (so im guessing 12mm spot size) and with 15j if im not wrong with 20ms pulse width - had this time full shadding and now i have some spots with no hair and some with finer shorter hairs…
on my back i made 5 treatments starting with 2 treatments with lightsheer (dont know the settings) then 2 more with an IPL which turns out to be waste of time and treatments (my clinic takes it in levels - when you have dark hair they use the lightsheer , then when the hairs get finer they move you to the quanta IPL , and then when i insisted they moved me to the alexandrite)
so last 2 treatments were with the alexandrite with settings:
20ms pulse width , 20j , dont know the spot size - i will get this next time i go.
and last treatment was with 5ms pulse width, 20j .
i waited 3 month between each last 2 treatments because they have told me it will have greater effect…
another question i have , sorry for all this questions at once…
if i have fine hairs , wouldnt it mean they have less deeper roots then black dark hairs ? if so, wouldnt it mean that less spot size is better at focusing on their root ?
I’ve tried lowering the spot size and raising the joules for finer hair on my abdomen, but it didn’t work that well anyway. fine hair is just hard to treat, period. you can try increasing the joules and decreasing the spot size a bit, but lowering the spot size too much is also ineffective because then it won’t penetrate deep enough to reach even the fine hair.
I used GentleLASE. On that machine, pulse is set at 3ms and can’t be changed. 20 joules is max on 18mm and 30 joules is max on 15mm. Either of those settings are fine to use. You need to try to see what works best for you specifically since we don’t know how coarse and how deep your hair is. Hair on upper arms and shoulders is hard to treat. keep that in mind. people usually need more treatments on those areas and you should really have pretty coarse and dense hair there for it to work somewhat well.
I think switching to an alex is a good idea. If you’re seeing full shedding, that’s a good sign. The treatments where you didn’t, you were probably undertreated. On the alex, I would try for lowest pulse (5ms is good) and 24-30 joules depending on how light your skin is, at 15mm.
Actually it doesn’t work like that. The settings on the machine are in joules fluence which is JF = joules/area (cm squared). Therefore the power already takes into account the spot size. So for a given hair with in the energy density of the spot, a 30 joules pulse is 50% more energy than a 20 joules pulse. Again everything is in joules fluence.
Fine hair doesn’t necessarily mean shallow and coarse hair doesn’t necessarily mean deep. And it is not just the depth of the hair but the effective cross section of the pulse at depth. What that means is that as the pulse penetrates into the skin, it begins to shrink (inverted cone). That also means that as a percentage of the skin that is pulsed, the effective pulse at depth shrinks and hair that appears to be within the pulse may not actually be within the effective zone, even though the pulse is otherwise deep enough.
Finally, the pulse causes a gradient to occur within the skin, so treating a shallow hair with a larger spot size is quite effective.
Actually it doesn’t work like that. The settings on the machine are in joules fluence which is JF = joules/area (cm squared). Therefore the power already takes into account the spot size. So for a given hair with in the energy density of the spot, a 30 joules pulse is 50% more energy than a 20 joules pulse. Again everything is in joules fluence.
so what was wrong with my calculation? for constant spot size , lets say 15mm you will get at 20 fluence a 35.325 J , and at 30 fluence 53J . so yes that is a about 35% more energy.
but if you compare bigger spot size with lower fluence to smaller spot size with higher fluence, like 18mm 20 fleunce and 15mm 30 fluence , you will get about the same amount of energy, no?
so that means that it is always better treating at the max spot size and max fluence… so why having the lower spot size anyway?
sslhr , what you mean by the cross section of the pulse is that because the laser is in an inverted cone shape when it penetrates the skin , so when the energy gets to the deeper section of the skin it is concentrated in a very small area and not as wide as in the upper levels of the skin , right? , so that means that if a person have very deep rooted hairs , most of them will not be effected at all at their bulb with each pulse, so that is another reason for continuing treatments…
Finally, the pulse causes a gradient to occur within the skin, so treating a shallow hair with a larger spot size is quite effective.
what this means? this means that the same amount of energy will hit the hair at diffrent depth levels? from what i know gradient means a bigger concentration in one area which causes a diffusion…
now im starting to understand the spot size and fluence , but there is one more thing which i don’t really understand, how is the pulse width effects the effectivness of the treatment? i have read that the pulse width should be the same or lower then the TRT of the hair follicle and the TRT is based on the hair size , but i also saw that the TRT of the epidermis is very very low , between 1-10 ms or so… correct me on this if i am wrong please… so can’t 5ms pulse cause more damage to the skin then 10ms or 20ms ? and which pulse width is better anyway ? does it deepends on the hair size in the treatment area or not ?
sslhr , from your expirience can a treatment on the shoulders and upper hands be effective? and in what terms it is diffrent then treating back / chest / belly or any other area?
You got the math right. But I think you are confusing total power which is what joules gives you with what you are calculating with joules fluence which is the power that arrives at the target. I think we are saying the same thing, but just in a different way.
Look at it this way. If I take a magnifying glass and hold it up in the sun, the power in that beam never changes. It is a function of the size of the glass and how many photons pass through it. This is total power. Now the power that arrives at the target, let’s say a leaf, is a function of how concentrated is the beam. This is energy density and is calculated in joules fluence. So with the same amount of power but not holding the glass in the right spot you do nothing to the leaf. But move the glass to the right spot so that all the photons are concentrated into a tiny spot and the leaf catches on fire. What ultimately matters is not the power in the pulse but the power that arrives at the target and this is joules fluence.
so that means that it is always better treating at the max spot size and max fluence… so why having the lower spot size anyway?
No not really. What you are doing is trading off power density for penetration. Ultimately the most important thing is penetration. If you are not deep enough then there will be no cellular destruction of the hair bulb. But you can’t have max power (Everything about power is about fluence) and the deepest penetration, so you have to balance the two. So a 20 mm spot size would be better but not at 16 joules max power. 16 joules just isn’t really enough. 20 joules is in most cases. And it turns out that for most treatments 18 mm spot at 20 is better than 15 mm at 30. But not always. The shallower the hair the less important the 18 mm spot.
sslhr , what you mean by the cross section of the pulse is that because the laser is in an inverted cone shape when it penetrates the skin , so when the energy gets to the deeper section of the skin it is concentrated in a very small area and not as wide as in the upper levels of the skin , right? , so that means that if a person have very deep rooted hairs , most of them will not be effected at all at their bulb with each pulse, so that is another reason for continuing treatments…
Actually that isn’t right. The beam on most lasers is actually a diverging beam where the beam is expanding as it leaves the barrel. This is a safety issue. The spacer on the handpiece allows the beam to be the right size when it hits the target (skin). What you are really getting is not so much a cone of photons but a cone of scatter, so that individual photons are scattering either outward or inward. Those that scatter inward contribute to the effective zone while those that scatter outward are lost. This is the gradient that occurs.
what this means? this means that the same amount of energy will hit the hair at diffrent depth levels? from what i know gradient means a bigger concentration in one area which causes a diffusion…
So what is happening is that you are losing photons on the edge and there is a gradient where the highest number of photons are found just under the skin. As you move further down the gradients form an inverted cone where the edge of the cone is the limit of effectiveness. Furthermore, the drop off from this limit is quite steep. The limit is a function of the scatter and spot size, and not related to power. This is one of those concepts that is easier to show than explain in writing.
now im starting to understand the spot size and fluence , but there is one more thing which i don’t really understand, how is the pulse width effects the effectivness of the treatment? i have read that the pulse width should be the same or lower then the TRT of the hair follicle and the TRT is based on the hair size , but i also saw that the TRT of the epidermis is very very low , between 1-10 ms or so… correct me on this if i am wrong please… so can’t 5ms pulse cause more damage to the skin then 10ms or 20ms ? and which pulse width is better anyway ? does it deepends on the hair size in the treatment area or not ?
Absolutely, the shorter the pulsewidth the more risk to the skin. But if you have a fine hair, it can not be treated with a long pulsewidth because it will lose more heat as it absorbs energy. Think of these two questions. 1) A crock pot with out a lid, will never cook. Why is that? 2) If it takes 1 min in a microwave to boil a cup of water, how much time does it take for a thimble of water to boil? Or for that matter, a drop of water the size of a cell? Now how much time does it take for that same drop of water to cool down. This is what thermal relaxation time and pulsewidth is all about.
What ultimately matters is not the power in the pulse but the power that arrives at the target and this is joules fluence.
now you got me all confused …
so trying to understand what you just said, the spot size only counts for the depth which the photons can get to and the fluence is the amount of power which gets to the hair. if that is right then 30j on 15mm will deliver more power to the hairs at less deeper level, then 20j on 18mm , which will deliver less power to hairs at deeper level?
but then your previous posts about this subject don’t make sense, because there you have told that the fluence is already calculated into the spot size, so the power of 20j on 18mm and 30j on 15mm are about the same… hmm…
also, how then do one knows the TRT of a specific hair? the coarser it is the higher TRT it has ? , and as a rule it is always better then to treat with lower pulse width as long as the skin can handle it right?
sslhr , one more thing, sslhr , can you tell from your expirience if treatments on the shoulders and upper hands are effective? and how come it is diffrent then treating back / chest / belly or any other area ?
What confuses everyone is the difference between joules and joules fluence. And all the numbers that are used in the industry are in joules fluence not in joules. Think of it this way, joules is related to power which is the total number of photons in the pulse. Joules fluence is the energy density or the density of photons at the skin (target). The density of photons (joules fluence) is based on the spot size.
So in the example above. Both 20 joules fluence at 18 mm spot and 30 joules fluence at 15 mm spot have similar number of photons. That is why they have similar amount of power. But at the target (skin) the photon density of the 15 mm spot size is 33% more than the photon density of the 18 mm spot (difference between 30 joules fluence and 20 joules fluence).
also, how then do one knows the TRT of a specific hair? the coarser it is the higher TRT it has ? , and as a rule it is always better then to treat with lower pulse width as long as the skin can handle it right?
Yes to a point. As the pulse width gets shorter and shorter you stop having thermal effects and start having shock effects where the laser pulse creates a shock wave. But this doesn’t really happen until you get below 1 millisecond.
[/quote]sslhr , one more thing, sslhr , can you tell from your expirience if treatments on the shoulders and upper hands are effective? and how come it is diffrent then treating back / chest / belly or any other area ? [/quote]
There are differences in how hair grows, the amount of hair actively growing at one time, and how deep they grow. This is why hair on your head is different from hair on your back or chest or legs or pubic area. And all of this has an impact on the treatments.
