Cancer Research Journal

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1 Cncer Reserch Journl 2014; 2(2): Pulished online April 20, 2014 ( doi: /j.crj The role of using ultr short pulsed lsers in determining dynmicl dependent of free electron density in the skin tissue for tretment of skin cncer S. Nsrin Hosseinimotlgh, Smir Khzrei Deprtment of Physics, Shirz rnch Islmic Azd University, Shirz, Irn Emil ddress: (S. N. Hosseinimotlgh), (S. Khzrei) To cite this rticle: S. Nsrin Hosseinimotlgh, Smir Khzrei. The Role of Using Ultr Short Pulsed Lsers in Determining Dynmicl Dependent of Free Electron Density in the Skin Tissue for Tretment of Skin Cncer. Cncer Reserch Journl. Vol. 2, No. 2, 2014, pp doi: /j.crj Astrct: We study on the new dvnces in lser cell surgery for skin cncer tretment nd investigte on the working mechnisms of femtosecondlser. Also, influences of the criticl electron density nd rdition intensity on the freeelectron density for ltion on the epidermis nd dermis tissues re investigted. Our studies on this work, show tht if the mount of rdition intensity of pulsed lser is incresed then the distnce of focl spot is decresed lso the mount of time dependent free- electron density ecome more nd more, such tht this cse is proper for skin cncer tretment. Also, our clcultions for skin tissue show tht optimum time dependent free electron density for dermis lyer t ngle 16 nd 22 which is function of wvelength, em width, em rdius, mplitude of the em rdition strength nd pulse durtion is more thn for epidermis lyer. Keywords: Skin, Tissue, Plsm, Ultr-Short 1. Introduction The gret progress in lser tretment in clinicl pplictions is primrily ttriuted to the rpid development of pulsed lser systems. The use of highly focused pulsed lser em to modify nd mnipulte tissue medium for pplictions in moleculr nd cellulr iophysics nd iotechnology ecomes more pervsive [1,2]. Ultrfst lsers output ultr-short pulses with pulse widths rnging from picoseconds down to femtoseconds. Short-pulse lsers hve ecome gretly importnt in recent yers for mny technologies, including lser clening, nd medicl nd iologicl pplictions. Applictions include dissection or inctivtion of cellulr orgnelles nd chromosomes with sumicron sptil precision [3], nd gene delivery through trnsient memrne disruption [4], to nme few. As the pulsed lser micro em technologies continue to dvnce, the fundmentl knowledge of lsertissue interction mechnisms is of vitl importnce nd could provide frmework where in systemtic investigtion of novel pulsed micro em techniques cn e developed. The plsm-medited ltion model hs een employed to explin the opticl rekdown phenomenon in the visile nd ner-infrred wvelength region, in which plsm induced y the strong electromgnetic field of short lser pulse without significnt light sorption, is considered s the cuse of rekdown [1, 5 6].During opticl rekdown, very high density of free electrons, i.e., plsm, of the order of 10 10, is produced. The mechnism, chromophor ioniztion, is responsile for lser-induced opticl rekdown, which results in geometric increse in the free-electron density. Plsm formtion is chrcterized y the growth of plsms. Docchio et l. [7, 8] estimted the moving rekdown model to nlyze plsm strting times nd the temporl nd sptil dynmics of plsm expnsion in liquids suject to nnosecond lser pulse irrdition. Fn et l. [10] modified the model y tking into ccount the pulse propgtion to chrcterize the time nd spce dependent rekdown region induced y femtosecond lser pulses. Recently, Zhou et l. [11] used the rte eqution to investigte the kinetic progression of plsm in pure wter generted y focused short lser pulses. Recently, Guo s group investigted plsm-induced ltion [12, 13] s well s therml interction [14] of focused short lser pulses with skin tissues. It is now cknowledged tht pulses with very short durtions, such s picosecond or femtosecond, re

2 34 S. Nsrin Hosseinimotlgh nd Smir Khzrei: The Role of Using Ultr Short Pulsed Lsers in Determining Dynmicl Dependent of Free Electron Density in the Skin Tissue for Tretment of Skin Cncer dvntgeous in mny pplictions. Due to the extremely short pulse durtion which is much shorter thn the therml relxtion time of mny mterils, lser interction with mterils occurs efore het diffusion ever tkes plce, leding to incresed locl temperture rise in very short time period nd minimiztion of het-ffecting zone. This will lessen therml dmge to the surroundings. Then the ltion of skin tissue with pico nd femtosecond lser pulses is investigted. In this pper, we discussed the interction fundmentls etween ultr short lser with skin tissue. The model skin tissue is n xisymmetric cylinder nd re strtified s three lyers with different opticl properties similr to humn skin tissues epidermis, dermis, nd sucutneous ft, respectively. The ultr short lser pulse is converged inside the skin tissue to induce plsm rekdown for lting cncerous tissue. The intensity of the focused em is clculted y the Beer-Lmert lw, nd the time-dependent freeelectron density is otined ccording to fourth-order Runge-Kutt method. Vrious ioniztion mechnism such s chromophore is clculted to show effects on the tissue lyers. In this model, the temporl evolution of free electrons (i.e. plsms) is predicted y rte eqution. The temporl evolution of the free-electron density is lso illustrted t different loctions inside the skin tissue. Finlly, we conclude tht of the influences of the free electron density rte eqution nd the chromophore ioniztion rte, em rdius, mplitude of the em rdition strength on the ltion in humn skin. 2. Mthemticl Models " 5 6!,7,89 ) " 679:;<=&4?2@ A CDC E FFGHI J K 2.1. Time-Dependent Eqution of Rditive Trnsfer (ERT) Consider converging short lser pulse upon iologicl tissue cylinder is sketched in Figure (1).[14]. The lser em rdition het trnsfer is descried y the time-dependent ERT in the cylindricl coordinte system s where,, re the three directionl cosines for the discrete direction is the rditive source term (the superscript is the index of discrete directions), c is the speed of light in tissue medium, I is the rdition intensity, is the extinction coefficient tht is the sum of the sorption coefficient nd the scttering coefficient, t is the time[16]!" # $ & ' " # $ ( " # ) * ) 1,2,.,/ (1) Once the intensity field is otined, the incident rdition is clculted s [16, 17] 0 ) 3 # 42 " " 5 (2) The incident rdition is the totl intensity impinging on point from ll directions. For n extremely wekly scttering medium like skin tissue, the vlue of the incident rdition equls to the llistic lser irrdince " 5. The rdition intensity hs two components: the llistic component " 5 ccounting for the incident lser em nd the diffuse component " # stnding for the scttering component of the lser em. The llistic component of lser em is expressed s [15-16] & 2L M:;<N O P6(9 OQ:;<A& R S (( E TUV J (3) Where c is the speed of light in the tissue; Wis the ngle etween the incident lser nd the opticl xis; 8 X is the pulse width t hlf mximum; is the extinction coefficient, which is the summtion of the sorption coefficient nd the scttering coefficient. The totl time durtion of whole pulse is set s 4tp in this study, so tht the pek of the pulse rrives t time 2tp. In our clcultions we ssumed tht verge lser power is 0.065W.The mplitude of the em rdition strength " 6Y9 cn e specified y eqution following " 6Y9 ) Z [P6(9 O (4) Bem spot size 2 is function of xil position z, nd it is chrcterized y em wist 2 t the focl point nd t the Ryleigh rnge or focl region Y \ s following ]14]: 26Y9 ) 2 \ ^1 A _ J _` O (5) Where 2 \ is the em wist t the focus; nd Y \ is Ryleigh length tht is clculted y Y \ ) c[p E`O λd O (6) Where, n is the refrctive index of the medium; λ the lser wvelength in free spce; e is the em qulity fctor tht is expressed s e ) P E`V` VP E (7) Here, W \ is the fr-field divergence of rel em; 2 nd W rethe em wist nd fr-field divergence of true Gussin em, respectively. In our clcultions we ssume tht e = 1 for skin tissue.

3 Cncer Reserch Journl 2014; 2(2): Rte Eqution The generl form of the rte eqution of the time evolution of the free electron density is given y [17]. f ) Af J gx Af J Th TTi &ji & T i (8) Figure 1.Sketch of the geometricl coordintes nd dimension[14]. Where i is the time dependent free-electron density. The first three terms on the right hnd side represent the production of free electrons through multi photon, chromophore nd cscde (vlnch) ioniztions, respectively. Lst two terms re the electron losses due to diffusion nd recomintion, respectively. The multi photon nd cscde (vlnch) ioniztions nd diffusion rtes re expressed s [14] TT ) ħ J o O A f J gx k P l[ Agm P A O z 0 & gzpo J (10) P O z O { Tcg rs E d j ) z r. ^A A g P E`J J (11) _` The recomintion rte is considered to e i Th 689 ) [ Th/ 5 N t A r 69 / :;<=& T Fˆ FˆŠ FˆJQ O N 0Q t :;<62u9vwx2u & r y (9) pg m rp O Tcs E ħp η ~ )2 10 l cm /s [18]. The ioniztion energy is E = 6.5 ev nd E = 4.6 ev for wter medium [19] nd skin tissue [20], respectively. The second term on the right hnd side eq.(5), the qusi-free-electron density due to chromophore ioniztion is estimted s [20] r 6Ž9 t ^Œ E { F Fˆ Fˆ Fˆ M (12) A necessry condition for the chromophore ioniztion pthwy in producing qusi-free electrons lie in ditic heting of the chromophores y the ultr short lser pulses. The chrcteristics time of therml energy trnsport out of n descried chromophore is proposed to e 20 µs [20]. Therefor, the ditic heting condition cn e ssumed for the ltion induced duo to picosecond or femtosecond lser interction within ech medium. Where 689 ) 0689dt is the time dependent integrl of the incident rdition: Th ~1 10 is the numer density of chromophores in skin tissue, / 5 k 1 10 is the verge numer of ound electrons per chromophore, Th ) š œ o mss density, u is the Boltzmnn constnt; is the mient temperture ssumed to e 300 K, Th ) t is the specific het of melnosome orgnelles, Th k 0.5% is the volume rtio of the chromophores to skin [20]. By tking prtil derivtive of the free-electron density with respect to time, the chromophore ioniztion rte is clculted Properties of Skin Tissue In this pper, for compring our otined results of skin tissue, we re considered the common wvelengths 532, 580 nd 1064 nm. A constnt sorption nd scttering coefficients of the plsms generted y the pulsed lser is ssumed. The epidermis lyer sorption coefficient is dopted s # = 0.02 nd for dermis is # = 0.05, the opticl properties of the tissues for medium t three wvelength re listed in Tle 1.In this work, humn skin (H=5mm, R=5mm) is orgnized in distinct lyers nd cylindricl coordinte vriles re z nd r. Which the high of epidermis, dermis nd sucutneous ft re, (H e =0.5mm), (H d =1.5mm), (H f =3mm), respectively. In this pper, the focused lser em will incident on the surfce of the epidermis nd dermis lyers within skin tissue. To induce plsm ltion in medium, use of ultr short pulsed (USP) lsers with pulse durtion down to picoseconds or femtoseconds is required. The opticl properties of the skin tissues t different wvelengths re listed in Tle 1. The refrctive index of the skin tissues is ssumed to e constnt t 1.40 [21]. Tle 1. Opticl properties of the skin tissues t wvelength 1064nm [21] Epidermis Results nd Discussion Dermis Ft Using the presented models nd ville dt, we consider the time dependent free electron density in skin tissue. There for, lser em is ssumed to e converged to smll spot t the skin lyer y single ojective lens with ngle of 16 nd 22 degree. Now the study on the plsm-medited ltion is extended to the model nd skin tissue for different lyers. A focused lser em will incident on the surfce of the epidermis or inside (dermis) in skin tissue. The focused lser em technology is

4 36 S. Nsrin Hosseinimotlgh nd Smir Khzrei: The Role of Using Ultr Short Pulsed Lsers in Determining Dynmicl Dependent of Free Electron Density in the Skin Tissue for Tretment of Skin Cncer dopted to its propgtion in the skin tissue is simulted vi solving the kinetic eqution of rditive trnsfer with Rung- Kutt method. In the numericl model, the opticl rekdown in the skin tissue is identified when the mximum free- electron density generted t the focl spot center during the period of one lser pulse equls to criticl electron density. In this work, we clculted the time evolution of the free-electron density in control volume. The technique of converging em is noninvsive method which idelly delivers energy to loction inside the ody nd voids undesirle rections in the surrounding helthy tissues. To study on the ltion in iologicl tissue, the ttenution of lights due to the sorption nd scttering effects re such tht needs to e ccurtely tken into ccount. Our numericl clcultions for free electron density t three wvelength show tht, the highest free-electron density would e occured in the lyer dermis t 16 degree. Figure 2.Comprison of the skin tissue nd wter medium ) 2(z) ) " 679s functions of the Z ( ). Tle 2.Comprison 2(z) nd" 679 clculted in the skin tissue wter medium. λ6º 9 ³ 6 9 ²«6¹ 9 «A. ± ±J «A. ² ±J «A. ±J µ 6 9 ³ 6 9 «A. ± ±J «A. ² ±J «A. ±J Figure 2() show the distnce vritions of 2(z) (em rdius) eq.5, for vrious wvelengths such s 532,580,1064 nm t different physicl conditions tht re listed in Tle 2 for wter medium (solid line) nd skin tissue (spot line). Here we estimted2(z) produced y lser pulse 30 ps t wvelength 1064 nm is mximum nd the lser pulse 6000 ns t wvelength 532 is minimum. We find tht 2(z) in the wter medium much is greter thn tht for skin tissue, due to differences in the refrctive index, hence, the Ryleigh length clculted is different. Fig. 2() show the distnce vritions of " 679 (em rdition strength) eq.4 for vrious wvelengths t different physicl conditions tht for wter medium(solid line) nd skin tissue (spot line). " 679clculted in the skin tissue is more thn wter medium, duo to differences in the refrctive index nd the Ryleigh length clculted, then mximum clculte " 679 from the focus spot the incoming lser em (z=0). The mximum irrdince is lwys t the em focus [14]. The extinction coefficient is from the lyers dermis 1.88 nd epidermis Figure 3. Comprison of " 5 A ¼ TgOJ s function of the!6μ 9¾? Y6 9 in the wvelength 532 nm for 22 \ ) 3.4 nd 22 \ ) 5.3 t two ngles 16,22 for dermis nd epidermis lyers of skin tissue.

5 Cncer Reserch Journl 2014; 2(2): Figure 4. Comprison of " 5 A ¼ TgOJ s function of the!6μ 9 ¾? Y6 9t the wvelength 1064 nm for 22 \ ) 4.7 nd 22 \ ) 7.7 t two ngles 16,22 for dermis nd epidermis lyers of skin tissue Figure 5. Comprison of " 5 A ¼ Tg OJ s function of the!6μ 9,Y6 9 in the wvelength 580 nm nd 22 \ ) 5, t P=3 pst two ngles 16,22 for dermis nd epidermis lyers of skin tissue. Figure 6. Comprison of " 5 A ¼ Tg OJs function of the!6μ 9,Y6 9 in the wvelength 580 nm nd 22 \ ) 5, t P=0.3 pst two ngles 16,22 for dermis nd epidermis lyers of skin tissue. Figure 7. Comprison of " 5 A ¼ Tg OJin terms of!6μ 9 ¾? Y6 9t the wvelength 580 nm nd 22 \ ) 4.4, t P=30 pst two ngles 16,22 for dermis nd epidermis lyers ) Wter medium ) Skin tissue. Figure 5-7 shows intensity rdition lser in the wter medium nd skin tissue with the 0.3 ps,30ps nd 3 ps pulses the lyers configurtion with considerd mount, ngle, pulse durtion nd the lyers depth nd distnce of focl spot, the first lyer is dermis 16 nd second lyer is dermis 22, the 3 rd lyer is epidermis 16 nd the lst lyer is epidermis 22.Also,in fig 3 to 7,we will find tht the good greement is seen etween intensity rdition lser nd lyers configurtion with cylinder rdius in the distnce vrtions. As expressed in eq.(3), the I 5 is depends on the extinction coefficient, ngle nd lyers depth counter. Our numericl clcultions show tht I 5 in the skin tissue is much greter thn wter medium, due to differences in the refrctive index, the Ryleigh length, em rdius nd " 679 clculted. There re not differences of viewpoint I 5 mount etween lyers configurtion for skin tissue in the 2-D nd 3-D models. The multi photon nd cscde ioniztions re the primry mechnisms for the USP lser ltion on the model skin tissue [14]. The chromophore ioniztion it should e pointed out tht in the presented re clcultions, the properties of the chromophores re ssumed to e the sme s the melnosome [14]. A USP lser system t wvelengths 532, 580, 1064 nm is considered. The free-electron density ws estimted in the orders of We ssumed verge lser power is 0.065W nd cylinderrdius is (r= ). For chromophore ioniztion with the picosecond nd the femtosecond pulses, t ll the wvelengths 532, 580 nd 1064 nm, from our clcultions results we found tht the good greements etween ngle nd the lyer depth nd the distnce of focl spot. For exmple, ccording to our clcultions for skin tissue show tht mximum of generted chromophoreioniztion t three wvelength for dermis lyer t ngles 16 nd 22 is more thn for epidermis lyer. As expressed in (9)-(12), the multi photon ioniztion rte is proportionl to 0 nd the chromophore ioniztion rte depends on the sorption of lser pulse energy 689 [14]. The chromophore ioniztion does not contriute too much to the genertion of the seed electrons ecuse of the reltively wek sorption of the chromophores ( =1.85 ) t mentionedwvelengths[14]. Therefore, in the following clcultions concerning the chromophore ioniztion in skin tissues induced y thepicosecond nd femtosecond lsers. Figure 3 to 8, show tht the vritions of choromophore ioniztion in terms of time for skin tissue t certin physicl condition.according to our clcultions the mximum of generted chromophore ioniztion t the wvelength 532 nm with 6000 ps pulse durtion of lyer dermis ngle 16 t the time of  s is , for skin tissue.

6 38 S. Nsrin Hosseinimotlgh nd Smir Khzrei: The Role of Using Ultr Short Pulsed Lsers in Determining Dynmicl Dependent of Free Electron Density in the Skin Tissue for Tretment of Skin Cncer Figure 8. Comprison of the choromophore ioniztion s function of the time in the wvelength 532 nm t two ngles 16,22 for dermis nd epidermis lyers )22 \ ) 5.3 )22 \ ) 3.4 in the skin tissue. Figure 9. Comprison of the chromophore ioniztion s function of the time in the wvelength 580 nm t two ngles 16,22 for dermis nd epidermis lyers)22 \ ) 5 )22 \ ) 5 nd8 X ) 0.3 ps in the skin tissue. Figure 10. Comprison of the chromophore ioniztion s function of the time in the wvelength 1064 nm t two ngles 16,22 for dermis nd epidermis lyers )22 \ ) 7.7 nd8 X ) 6000<)22 \ ) 4.7 nd8 X ) 30<in the skin tissue. The minimum of generted chromophor ioniztion t the 3 ps pulse t wvelength 580 nm nd ngle 22 of epidermis lyer t the time of sis for skin tissue. Figure 9 shows chromophore ioniztion in skin tissue with the 0.3 ps nd 0.1 pulses the lyers configurtion with considered mount, ngle, pulse durtion nd the time integrl of the incident rdition nd distnce of focl spot. The lyers configurtion duo to genertedchromophor ioniztion t the different pulses nd wvelengths re, dermis 16, dermis 22, epidermis 16 nd

7 Cncer Reserch Journl 2014; 2(2): epidermis 22,respectively.There re not differences of the viewpoint mount chromophore ioniztion in the lyers configurtion etween for ech mediumm in the 2-D nd 3-D models, ut from results of our clcultions we found tht differences re etween lyers configurtion in the chromophore ioniztion with free electron density t skin tissue these differences re due to choose the Runge Kutt lgorithm nd criticl electron density. Also, in fig 8 to10, we see tht the two dimensionl digrms of time dependent free electron density for different wvelengths t vrious physicl conditions for skin tissue (epidermis nd dermis) t choosing the incident ngles 16 nd 22. Figure 11. Comprison of the free electron density s function of the time in the wvelength 532 nm )22 \ ) 5.3 nd8 X ) 6000<)22 \ ) 3.4 nd8 X ) 30<in the skin tissue. Tle 3. Comprison of the pek spot the free electron density in the skin tissue for wvelength 532 nm with 22 \ ) 5.3 nd 8 X ) 6000< t two ngles 16,22 for dermis nd epidermis lyers. Å ÆÇ 6µ9Æ Dermis-ngle p Epidermisngle p Dermisngle p epidermisngle Tle 4. Comprison of the pek spot the free electron density in the skin tissue for wvelength 532 nm with 22 \ ) 3.4 nd 8 X ) 30< t two ngles 16,22 for dermis nd epidermis lyers. Figure 12. Comprison of the free electron density s function of the time in the wvelength 580 nm t two ngles 16,22 for dermis nd epidermis lyers )22 \ ) 5 nd8 X ) 3<. Å ÆÇ 6µ9Æ Tle 5. Comprison of the pek spot the free electron density in the skin tissue for wvelength 580 nm with 22 \ ) 5, 8 X ) 3<t two ngles 16,22 for dermis nd epidermis lyers. Dermis-ngle 16 epidermisngle16 Dermis-ngle l 0 p 0 l Dermis-ngle 16 epidermisngle16 Dermisngle ÅÆÇ 6µ9Æ Epidermisngle p epidermisngle p 1.125

8 40 S. Nsrin Hosseinimotlgh nd Smir Khzrei: The Role of Using Ultr Short Pulsed Lsers in Determining Dynmicl Dependent of Free Electron Density in the Skin Tissue for Tretment of Skin Cncer Figure 13. Comprison of the free electron density s function of the time in the wvelength 1064 nm t two ngles 16,22 for dermis nd epidermis lyers )22 \ ) 7.7 nd8 X ) 6000<)22 \ ) 4.7 nd8 X ) 30<in the skin tissue. Tle 6. Comprison of the pek spot the free electron density in the skin tissue for wvelength 1064 nm with 22 \ ) 7.7 nd 8 X ) 6000<t two ngles 16,22 for dermis nd epidermis lyers p p Å ÆÇ 6µ9Æ Tle 7. Comprison of the pek spot the free electron density in the skin tissue for wvelength 1064 nm with 22 \ ) 4.7 nd 8 X ) 30<t two ngles 16,22 for dermis nd epidermis lyers. Dermis-ngle 16 epidermisngle16 Dermisngle22 epidermisngle22 Dermis-ngle 16 epidermisngle16 Dermisngle22 epidermisngle Å ÆÇ 6µ9Æ In tles 3 to 7, our clcultions results of numericl vlues of intensity rdition lser, chromophor ioniztion nd time dependent free electron density for vrious wvelengths t different physicl conditions t two ngles 16 nd 22 for two lyers (epidermis nd dermis ) for skin tissue. By seeing the tle 3 to 7, we will find tht the good greement is seen etween free electron density nd criticl electron density nd lyers configurtion with considered wvelengths nd pulse durtions. Time dependent free electron density for wvelength of 1064 nm, with 6 ns pulse durtion is the slight difference with the other wvelengths t vrious physicl conditions from the point view of lyersconfigurtion. According to our clcultions l 0 0 l the criticl free electron density in skin tissue t the wvelengths 1064 nm with6000ps pulse durtion of lyer dermis 22 is, , nd for lyer dermis 16 is zero. This difference is due to criticl free electron density, therefor, ccording to our clcultions, the mximum of generted free electron density t the dermis lyer of skin tissue re , for ngle 22 nd 16, respectively The mximum criticl free-electron density in skin tissue t 532 nm of nd with 30 ps pulse of dermis lyer 22 is, nd minimum t 580 nm with 3 ps pulse of epidermis lyer 22 is Our computions show tht for ltion in skin tissue t 580 nm wvelength with two pulse durtion 0.1 ps nd 0.3 ps the time dependent free electron density is out 0. This is duo to very short pulse durtion nd " 5 Ê 0. Our clcultions show tht free electron density nd chromophore ioniztion is ncresing with incresing time nd the time dependent integrl of the incident rdition nd the rdition intensity. For ltion with the picosecond nd femtosecond pulses, t ll the wvelength 532, 580 nd 1064 nm, from clcultions results we conclude tht the good greement etween lyers configurtion with considering ngle ndthe distnce of spot focl. Therefore from tle 3 to 7 we see tht concerning the ltion in skin tissue induced y the picosecond nd femtosecond lsers, mximum free electron density for wvelength 532 with 30 ps pulse durtion of dermis lyer t ngle 16 is in the time s for skin tissue. Therefor, ccording to our clcultions the minimum of generted free electron density of epidermis 22 t 3 ps pulse nd 580 nm wvelength t the time of sis 6 10, for skin tissue. From fig (11)-(13) we see tht the free electron density could expnd initilly of the occurrence of cscde ioniztion with more lser energy. Focused lser em ws incident on the surfce of the epidermis or inside the skin tissue. A USP lser system t wvelength 1064nm

9 Cncer Reserch Journl 2014; 2(2): with 30 ps pulse durtion is considered. The criticl freeelectron density would e estimted in the order of 10 & 10.To remove the cncerous cells exiting in the skin lyers effectively, lser em cn e focused inside the skin to the dermis ngle 16 degree surfce. The criticl electron density epidermis lyer is smll therefore, the free electron density is very smll in dermis lyer. 4. Conclusions In this work, our studies re estlished on the ultr short pulsed lser on the skin in cylindricl coordintes. The temporl evolutions of the free-electron density re clculted using numericl methods(fourth-order Runge- Kutt). A prmetric study with regrding to the free electron density (plsm) in the skin tissue on the dermis nd epidermis lyers t ngle 16 nd 22 degree re concluded. In this work, 2-D nd 3-D models re estlished in comining the chromophore ioniztion rte nd the I 5 to investigte the temporl evolutions of the freeelectron density in skin tissues. From our oting results we found tht the good greement etween lyers configurtion with considering ngle, the extinction coefficient, lyers depth nd the distnce of spot focl. Our studies on this work, show tht if the mount of rdition intensity of pulsed lser is incresed nd the distnce of focl spot is decresed, the mount of time dependent freeelectron density more nd more, such tht this cse is proper for skin cncer tretment. Also, our clcultions for skin tissue show tht optimum time dependent free electron density, I 5 nd the chromophore ioniztion rte for dermis lyer t ngle 16 nd 22 re functions of wvelength, em width, em rdius, mplitude of the em rdition strength. Also pulse durtion is more thn for epidermis lyer. Our clcultions show tht free electron density nd chromophore ioniztion is incresing with incresing time nd the time dependentintegrl of the incident rdition nd the rdition intensity. From clcultions results we found tht the good greement etween lyers configurtion of viewpoint mount for the free electron density rte eqution nd chromophore ioniztion with considering ngle nd distnce of focl spot nd I 5. The first lyer is dermis with ngle 16 degree, ltter lyer is dermis with 22 degree, the 3 rd lyer is epidermis 16 degree nd the lst lyer is epidermis 22 degree. The influence of vrious ioniztion mechnism including, chromophore ioniztion pthwys on the process of plsm genertion for the model skin tissue is investigted. A good greement is found etween lyers configurtion in 2-D nd 3-D models of choromophor ioniztion in skin tissue ut the slight differences re etween lyers configurtion in chromophore ioniztion with free electron density t skin tissue cn due to differences in the Runge Kutt lgorithm nd criticl electron density. References [1] Y.R. Shen, The Principles of Nonliner Optics (Wiley, New York,1984) [2] J. Ksprin, J. Solle, M. Richrd, J.-P. Wolf, Appl. Phys. B 79,947 (2004) [3] K.Köning, I.Riemnn,P.Fischer,K.Hlhuer,Cell.Mol.iol.45,195(199 9) [4] K.Schutze,G.Lhr,Nt.Biotechnol.16,737(1998) [5] J. Nock, A. Vogel, IEEE J. Quntum Electron. 35, 1156 (1999) [6] M.H. Niemz, E.G. Klncnik, J.F. Bille, Lsers Surg. Med. 11, 426(1991) [7] F.Docchio,P.Regondi,M.R.c.Cpon,J.Mellerio,ppl.Opt.27,3 661(1988) [8] F.Docchio,P.Regondi,M.R.c.Cpon,J.Mellerio,ppl.Opt.27,3 669(1988) [9] C.H.Fn, J. Sun, J.P. Longtin, J. Het Trnsf.124,275(2002) [10] J. Zhou, J.H. Chen, Y. Zhng, Appl. Phys. B 90,141(2008) [11] H.Hung,Z.Guo,J.Phys.D,Appl.Phys.42,165204(2009) [12] H. Hung, Z. Guo, Lsers Med.Sci.25,517(2010) [13]. J.Jio,Z.Guo,Phys.Med.Biol.54,4225(2009) [14] J. Jio, Z. Guo, Appl Phys,195,(2011) [15] H.Hung,Z.Guo,J.Phys.D,Appl.Phys.42,165204(2009) [16] H. Hung, Z. Guo, Lsers Med.Sci.25,517(2010) [17] J.Jio,Z.Guo,Phys.Med.Biol.54,4225(2009) [18] P. Kennedy, IEEE J. Quntum Electron.31,2241(1995) [19] F.Willim,S.p.Vrm,S.Hillenius,J.Chem.Phys.64,1549(197 6) [20] Q. Y. Fng, X. H. Hu, IEEE j,quntumelectron.40,69(2004) [21] H.Ding,J.Q.Lu,W..Wooden,P.J.Krgel,X.H.Hu,Phys.Med.B io.51,1479(2006)