{"id":4334,"date":"2026-02-09T13:22:15","date_gmt":"2026-02-09T12:22:15","guid":{"rendered":"https:\/\/www.swissrocketman.fr\/Wordpress\/?p=4334"},"modified":"2026-02-09T14:17:28","modified_gmt":"2026-02-09T13:17:28","slug":"operateur-de-faisceau-optique-passif-spectra-physics-bd-5","status":"publish","type":"post","link":"https:\/\/www.swissrocketman.fr\/Wordpress\/?p=4334","title":{"rendered":"Op\u00e9rateur de faisceau optique passif Spectra Physics BD-5"},"content":{"rendered":"

Le module Spectra-Physics BD-5<\/strong> est un op\u00e9rateur de faisceau optique passif<\/strong>, utilis\u00e9 surtout avec des lasers continus (Ar\u207a, Kr\u207a, He-Cd, DPSS, etc.). \u00c0 partir de tes photos (empilement de lames en verre \u00e0 angle, trace violette, bo\u00eetier Spectra-Physics), on peut \u00eatre tr\u00e8s pr\u00e9cis sur ce qu\u2019il fait<\/strong> et comment \u00e7a marche physiquement et math\u00e9matiquement<\/strong>.<\/h3>\n<\/div><\/section><\/div>\n

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Le BD-5<\/strong> est un beam attenuator + beam shaper<\/strong> :<\/p>\n

\ud83d\udc49 Il permet de :<\/p>\n

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    att\u00e9nuer la puissance<\/strong> du laser de fa\u00e7on continue et reproductible<\/strong><\/p>\n<\/li>\n

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    d\u00e9placer l\u00e9g\u00e8rement le faisceau<\/strong> sans changer sa direction globale<\/p>\n<\/li>\n

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    nettoyer spatialement<\/strong> le faisceau (suppression de r\u00e9flexions parasites)<\/p>\n<\/li>\n

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    travailler \u00e0 forte puissance<\/strong> sans br\u00fbler (optique en transmission, pas d\u2019absorption)<\/p>\n<\/li>\n<\/ul>\n

    Ce n\u2019est ni un modulateur rapide<\/strong>, ni un AOM, ni un EOM.<\/p>\n

    Ce qu\u2019on voit sur les photos<\/h2>\n

    Tu as exactement montr\u00e9 l\u2019int\u00e9rieur typique du BD-5 :<\/p>\n

    \ud83d\udd39 Empilement de lames en verre<\/h3>\n
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      Une pile de plaques optiques parall\u00e8les<\/strong><\/p>\n<\/li>\n

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      L\u00e9g\u00e8rement inclin\u00e9es<\/strong> par rapport au faisceau<\/p>\n<\/li>\n

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      Verre optique (BK7 ou \u00e9quivalent)<\/p>\n<\/li>\n

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      Non absorbantes<\/p>\n<\/li>\n<\/ul>\n

      \ud83d\udd39 Deux barres cuivre<\/h3>\n
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        Rigidit\u00e9 m\u00e9canique<\/p>\n<\/li>\n

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        Dissipation thermique indirecte<\/p>\n<\/li>\n

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        Maintien pr\u00e9cis de l\u2019angle<\/p>\n<\/li>\n<\/ul>\n

        \ud83d\udd39 Trace violette visible<\/h3>\n
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          Diffusion Rayleigh + r\u00e9flexions de surface<\/p>\n<\/li>\n

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          Typique d\u2019un laser bleu \/ violet (488 nm, 457 nm, 405 nm)<\/p>\n<\/li>\n<\/ul>\n

          \u00a0Principe physique fondamental<\/h2>\n

          Le BD-5 exploite les r\u00e9flexions de Fresnel<\/strong> sur des interfaces air\u2013verre.<\/p>\n<\/div><\/section>
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          Pourquoi l\u2019inclinaison est cruciale<\/h2>\n

          Les lames ne sont pas perpendiculaires<\/strong> au faisceau :<\/p>\n

          Effets recherch\u00e9s :<\/h3>\n
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            Les r\u00e9flexions parasites<\/strong> sortent du chemin optique<\/p>\n<\/li>\n

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            Le faisceau principal reste quasi colin\u00e9aire<\/strong><\/p>\n<\/li>\n

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            Pas de cavit\u00e9 parasite (\u00e9vite oscillations)<\/p>\n<\/li>\n<\/ol>\n

            D\u00e9placement lat\u00e9ral du faisceau<\/h3>\n

            Pour une lame d\u2019\u00e9paisseur e<\/em> inclin\u00e9e d\u2019un angle \u03b8 :<\/p>\n

            \u03b4=e\u22c5sin\u2061(\u03b8\u2212\u03b8\u2032)cos\u2061(\u03b8\u2032)\\delta = e \\cdot \\frac{\\sin(\\theta – \\theta’)}{\\cos(\\theta’)}<\/span>\u03b4<\/span>=<\/span><\/span>e<\/span>\u22c5<\/span><\/span>cos<\/span>(<\/span>\u03b8<\/span>\u2032<\/span><\/span><\/span><\/span>)<\/span>sin<\/span>(<\/span>\u03b8<\/span>\u2212<\/span>\u03b8<\/span>\u2032<\/span><\/span><\/span><\/span>)<\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/p>\n

            avec :<\/p>\n

            nsin\u2061\u03b8\u2032=sin\u2061\u03b8n \\sin \\theta’ = \\sin \\theta<\/span>n<\/span>sin<\/span>\u03b8<\/span>\u2032<\/span><\/span><\/span><\/span><\/span><\/span><\/span>=<\/span><\/span>sin<\/span>\u03b8<\/span><\/span><\/span><\/span><\/span><\/p>\n

            \u27a1\ufe0f Le BD-5 introduit un d\u00e9calage lat\u00e9ral<\/strong>, mais pas d\u2019angle de sortie<\/strong>.<\/p>\n

            Effet sur la qualit\u00e9 de faisceau<\/h2>\n

            Le BD-5 :<\/p>\n

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              ne focalise pas<\/strong><\/p>\n<\/li>\n

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              ne change pas M\u00b2<\/strong><\/p>\n<\/li>\n

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              ne modifie pas la divergence<\/strong><\/p>\n<\/li>\n<\/ul>\n

              Mais :<\/p>\n

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                supprime les franges parasites<\/p>\n<\/li>\n

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                am\u00e9liore la stabilit\u00e9 du point focal<\/p>\n<\/li>\n

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                agit comme un spatial cleaner passif<\/strong><\/p>\n<\/li>\n<\/ul>\n

                Puissance admissible (tr\u00e8s important)<\/h2>\n

                Comme il n\u2019y a pas d\u2019absorption<\/strong> significative :<\/p>\n

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                  Compatible avec plusieurs watts continus<\/strong><\/p>\n<\/li>\n

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                  Tr\u00e8s utilis\u00e9 avec :<\/p>\n

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                    Argon ion 488 \/ 514 nm<\/p>\n<\/li>\n

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                    Krypton<\/p>\n<\/li>\n

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                    DPSS multi-watts<\/p>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

                    Limite principale :<\/p>\n

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                      densit\u00e9 de puissance surfacique<\/strong><\/p>\n<\/li>\n

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                      qualit\u00e9 des traitements antireflet (s\u2019ils existent)<\/p>\n<\/li>\n<\/ul>\n

                      En r\u00e9sum\u00e9 clair<\/h2>\n
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                      Fonction<\/th>\nBD-5<\/th>\n<\/tr>\n<\/thead>\n
                      Att\u00e9nuation continue<\/td>\n\u2705<\/td>\n<\/tr>\n
                      Forte puissance<\/td>\n\u2705<\/td>\n<\/tr>\n
                      Passif \/ robuste<\/td>\n\u2705<\/td>\n<\/tr>\n
                      Modulation rapide<\/td>\n\u274c<\/td>\n<\/tr>\n
                      AOM \/ EOM<\/td>\n\u274c<\/td>\n<\/tr>\n
                      Filtre de longueur d\u2019onde<\/td>\n\u274c<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div><\/section><\/div>\n
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                      calculer l\u2019att\u00e9nuation exacte pour 25 lames et 915 nm 200w continu<\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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                      Parfait, on fait \u00e7a proprement et chiffr\u00e9<\/strong> \ud83d\udd2c
                      Hypoth\u00e8ses r\u00e9alistes pour un Spectra-Physics BD-5<\/strong> \u00e0 915 nm \u2013 200 W CW<\/strong>.<\/p>\n

                      Hypoth\u00e8ses optiques raisonnables<\/p>\n

                      Pour le BD-5 :<\/p>\n

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                        Lames en verre optique type BK7 \/ \u00e9quivalent<\/strong><\/p>\n<\/li>\n

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                        Pas de rev\u00eatement AR sophistiqu\u00e9 (ou AR simple ancien)<\/p>\n<\/li>\n

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                        Incidence faible (quelques degr\u00e9s)<\/p>\n<\/li>\n<\/ul>\n

                        \u00c0 915 nm<\/strong> :<\/p>\n

                        n\u22481,51n \\approx 1{,}51<\/span>n<\/span>\u2248<\/span><\/span>1<\/span>,<\/span><\/span>51<\/span><\/span><\/span><\/span><\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/article>\n<\/div><\/section><\/div>\n

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                        estimer la puissance max admissible avant fracture<\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
                        Tr\u00e8s bonne question \u2014 l\u00e0 on touche \u00e0 la vraie limite physique<\/strong> du BD-5 :<\/div>\n<\/div>\n<\/div>\n<\/article>\n
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                        \ud83d\udc49 la fracture thermo-m\u00e9canique des lames<\/strong>, pas l\u2019optique elle-m\u00eame.<\/p>\n

                        Je te fais une estimation quantitative r\u00e9aliste<\/strong>, \u00e9tape par \u00e9tape, pour 915 nm CW<\/strong>.<\/p>\n

                        \u00a0M\u00e9canisme r\u00e9el de rupture<\/p>\n

                        Pour des lames en verre (BK7 ou \u00e9quivalent), la rupture vient de :<\/p>\n

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                          absorption volumique r\u00e9siduelle<\/strong> (tr\u00e8s faible mais non nulle)<\/p>\n<\/li>\n

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                          gradient thermique transverse<\/strong><\/p>\n<\/li>\n

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                          contrainte m\u00e9canique \u03c3 > \u03c3\u1d63 (rupture)<\/strong><\/p>\n<\/li>\n<\/ul>\n

                          \u27a1\ufe0f Ce n\u2019est PAS la puissance totale<\/strong> qui casse la lame
                          \u27a1\ufe0f C\u2019est la densit\u00e9 de puissance + taille du faisceau<\/strong><\/p>\n

                          \u00a0Propri\u00e9t\u00e9s thermom\u00e9caniques du verre (BK7)<\/h2>\n

                          Valeurs typiques :<\/p>\n

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                          Param\u00e8tre<\/th>\nSymbole<\/th>\nValeur<\/th>\n<\/tr>\n<\/thead>\n
                          Conductivit\u00e9 thermique<\/td>\nk<\/td>\n1.1 W\u00b7m\u207b\u00b9\u00b7K\u207b\u00b9<\/td>\n<\/tr>\n
                          Coefficient dilatation<\/td>\n\u03b1<\/td>\n7.1\u00d710\u207b\u2076 K\u207b\u00b9<\/td>\n<\/tr>\n
                          Module d\u2019Young<\/td>\nE<\/td>\n82 GPa<\/td>\n<\/tr>\n
                          Coefficient de Poisson<\/td>\n\u03bd<\/td>\n0.206<\/td>\n<\/tr>\n
                          Contrainte de rupture (r\u00e9elle)<\/td>\n\u03c3\u1d63<\/td>\n30\u201350 MPa<\/td>\n<\/tr>\n
                          Absorption \u00e0 915 nm<\/td>\nA<\/td>\n~1\u00d710\u207b\u2074 cm\u207b\u00b9<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/article>\n<\/div><\/section><\/p><\/div>\n

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                          <\/div><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":4335,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4334","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-non-classe"],"_links":{"self":[{"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4334","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4334"}],"version-history":[{"count":13,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4334\/revisions"}],"predecessor-version":[{"id":4358,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/posts\/4334\/revisions\/4358"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=\/wp\/v2\/media\/4335"}],"wp:attachment":[{"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4334"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4334"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.swissrocketman.fr\/Wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4334"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}